Search

Various physical demands are placed on soldiers, whose effectiveness and survivability depend on their combat-specific physical fitness. Because sport training programs involving weight-based training have proven effective, this study examined the value of such a program for short-term military training using combat-relevant tests. A male weight-based training (WBT) group (n = 15; mean +/- SD: 27.0 +/- 4.7 years, 173.8 +/- 5.8 cm, 80.9 +/- 12.7 kg) performed full-body weight-based training workouts, 3.2-km runs, interval training, agility training, and progressively loaded 8-km backpack hikes. A male Army Standardized Physical Training (SPT) group (n = 17; mean +/- SD: 29.0 +/- 4.6 years, 179.7 +/- 8.2 cm, 84.5 +/- 10.4 kg) followed the new Army Standardized Physical Training program of stretching, varied calisthenics, movement drills, sprint intervals, shuttle running, and distance runs. Both groups exercised for 1.5 hours a day, 5 days a week for 8 weeks. The following training-induced changes were statistically significant (P < 0.05) for both training groups: 3.2-km run or walk with 32-kg load (minutes), 24.5 +/- 3.2 to 21.0 +/- 2.8 (SPT) and 24.9 +/- 2.8 to 21.1 +/- 2.2 (WBT); 400-m run with 18-kg load (seconds), 94.5 +/- 14.2 to 84.4 +/- 11.9 (SPT) and 100.1 +/- 16.1 to 84.0 +/- 8.4 (WBT); obstacle course with 18-kg load (seconds), 73.3 +/- 10.1 to 61.6 +/- 7.7 (SPT) and 66.8 +/- 10.0 to 60.1 +/- 8.7 (WBT); 5 30-m sprints to prone (seconds), 63.5 +/- 4.8 to 59.8 +/- 4.1 (SPT) and 60.4 +/- 4.2 to 58.9 +/- 2.7 (WBT); and 80-kg casualty rescue from 50 m (seconds), 65.8 +/- 40.0 to 42.1 +/- 9.9 (SPT) and 57.6 +/- 22.0 to 44.2 +/- 8.8 (WBT). Of these tests, only the obstacle course showed significant difference in improvement between the two training groups. Thus, for short-term (i.e., 8-week) training of relatively untrained men, the Army's new Standardized Physical Training program and a weight-based training experimental program can produce similar, significant, and meaningful improvements in military physical performance. Further research would be needed to determine whether weight-based training provides an advantage over a longer training period. [ABSTRACT FROM AUTHOR]

To examine correlates of the speed at which female soldiers carrying loads could cover 3.2 km on foot and traverse an obstacle course, 12 volunteers (mean +/- SD: 25.3 +/- 6 years, 166 +/- 7 cm, 61.3 +/- 7 kg) were timed over 3.2 km while carrying loads of 14, 27, and 41 kg, and while traversing an obstacle course with the two lighter loads. Pearson correlations showed that absolute VO[2max] and 3.2 km run time without a load were the best predictors of 3.2 km load carriage time for all loads. Also, larger subjects with greater muscle mass were able to carry the heaviest load faster than smaller, less muscular subjects, likely because the 41 kg load represented a smaller percentage of the former's bodyweight. Maximum number of sit-ups and push-ups, composite score of the Army Physical Fitness Test as well as body height were positively correlated with the speed at which some course segments were traversed. [ABSTRACT FROM AUTHOR]

To examine the importance of resistance training movement speed, two groups of women (24 +/- 4 years, 162 +/- 5 cm, 59 +/- 7 kg) squatted repeatedly at 1) 2 seconds up, 2 seconds down (slow, N = 11); or 2) 1 second up, 1 second down (fast, N = 10), doing three warm-up sets and three eight-repetition maximum sets, three times per week for 7 weeks. Tests included force platform and video analysis of the vertical jump, long jump, and maximum squat, and isometric and isokinetic knee extensor testing at speeds from 25 to 125 deg/sec. The groups improved similarly in many variables with training but also showed some differences. In the long jump, the fast group was superior in numerous variables including knee peak velocity and total-body vertical and absolute power. In the vertical jump, fast training affected the ankle and hip more (e.g., average power), and slow training mostly affected the knee (average torque). In isokinetic testing, the fast group improved strength most at the faster velocities, while the slow group strength changes were consistent across the velocities tested. Although both slow and fast training improved performance, faster training showed some advantages in quantity and magnitude of training effects. [ABSTRACT FROM AUTHOR]

Abstract: Cohen BS, Redmond JE, Haven CC, Foulis SA, Canino MC, Frykman PN, Sharp MA. Occupational Experience Effects on Physiological and Perceptual Responses of Common Soldiering Tasks. J Strength Cond Res 37(4): 894-901, 2023-This study measured the impact of occupational experience (i.e., time spent deployed, in military service, and in job and task performance frequency in training, deployment, and study practice) on the physiological (heart rate [HR] and oxygen consumption [VO 2 ]) and perceptual (rate of perceived exertion [RPE]) responses to performance of critical physically demanding tasks (CPDTs). Five CPDTs (road march, build a fighting position, move under fire, evacuate a casualty, and drag a casualty to safety), common to all soldiers, were performed by 237 active duty soldiers. Linear regression models examined the association between measures of experience and physiological and perceptual performance responses to task demands. The level of significance was adjusted for multiple comparisons and set at ρ ≤ 0.0125 for this study. Significant and notable effect sizes included the impact of time spent deployed on the physiological measures of the road march (PostHR F = 24.84, p < 0.0001, β=-9.65), sandbag fill (PostHR F = 8.26, p = 0.005, β = -2.83), and sandbag carry (MeanHR F = 7.51, p = 0.007, β = -1.12; PostHR F = 7.35, p = 0.007, β = -0.87). For the road march task, there was a nearly 10 bpm decrease in postperformance HR for every year spent deployed. Road march, sandbag fill, and sandbag carry tasks PostHRs were also notably negatively associated with the experience measures of time in their MOS (job and time in military service but not for other physiological and perceptual responses, including VO 2 and RPE. Frequency of task performance in training, deployment, and study practice was not meaningfully associated with experience. The results suggest that increasing task familiarization through on-the-job occupational operational experience may result in greater proficiency and reduced physiological effort., (Copyright © 2022 National Strength and Conditioning Association.)

Introduction: Existing predictive equations underestimate the metabolic costs of heavy military load carriage. Metabolic costs are specific to each type of military equipment, and backpack loads often impose the most sustained burden on the dismounted warfighter., Purpose: This study aimed to develop and validate an equation for estimating metabolic rates during heavy backpacking for the US Army Load Carriage Decision Aid (LCDA), an integrated software mission planning tool., Methods: Thirty healthy, active military-age adults (3 women, 27 men; age, 25 ± 7 yr; height, 1.74 ± 0.07 m; body mass, 77 ± 15 kg) walked for 6-21 min while carrying backpacks loaded up to 66% body mass at speeds between 0.45 and 1.97 m·s-1. A new predictive model, the LCDA backpacking equation, was developed on metabolic rate data calculated from indirect calorimetry. Model estimation performance was evaluated internally by k-fold cross-validation and externally against seven historical reference data sets. We tested if the 90% confidence interval of the mean paired difference was within equivalence limits equal to 10% of the measured metabolic rate. Estimation accuracy and level of agreement were also evaluated by the bias and concordance correlation coefficient (CCC), respectively., Results: Estimates from the LCDA backpacking equation were statistically equivalent (P < 0.01) to metabolic rates measured in the current study (bias, -0.01 ± 0.62 W·kg-1; CCC, 0.965) and from the seven independent data sets (bias, -0.08 ± 0.59 W·kg-1; CCC, 0.926)., Conclusions: The newly derived LCDA backpacking equation provides close estimates of steady-state metabolic energy expenditure during heavy load carriage. These advances enable further optimization of thermal-work strain monitoring, sports nutrition, and hydration strategies., (Copyright © 2022 Written work prepared by employees of the Federal Government as part of their official duties is, under the U.S. Copyright Act, a “work of the United States Government” for which copyright protection under Title 17 of the United States Code is not available. As such, copyright does not extend to the contributions of employees of the Federal Government.)

Introduction: The U.S. Army Occupational Physical Assessment Test (OPAT) is a pre-enlistment physical employment screening assessment developed to place recruits and soldiers into Military Occupational Specialties (MOSs) based on their physical capabilities in order to optimize performance and limit injury. The OPAT consists of the seated power throw (SPT), strength deadlift (SDL), standing long jump, and interval aerobic run. During the scientific validation of the OPAT, two variants of the SPT and two variants of the SDL were used. Although the OPAT was validated using both variants for each test, U.S. Army scientists and policymakers have received queries regarding how these variants compare to each other. Therefore, the purpose of this study was to compare different variants of the SPT and SDL., Materials and Methods: Thirty-two participants (14 male and 18 female) between the ages of 18 and 42 years visited the laboratory on one occasion and performed two variants of the SPT (seated on the ground [the current OPAT standard] versus seated in a chair with a 35 cm seat height) and two variants of the SDL (using a hex-bar [the current OPAT standard] versus using paired dumbbells). Testing order for the different variants was randomized. The protocol was approved by the U.S. Army Medical Research and Development Command Institutional Review Board., Results: Performing the SPT from a chair significantly (P < .05) increased performance when compared to performing the SPT from the ground (5.4 ± 1.3 m versus 5.0 ± 1.4 m, respectively). Values for the two SPT variants were correlated (tau = 0.90). Performing the SDL using the hex-bar significantly increased the maximal weight lifted when compared to performing the SDL using paired dumbbells (86.9 ± 18.4 kg versus 83.1 ± 18.0 kg, respectively). Values for the two SDL variants were correlated (tau = 0.83)., Conclusions: Performing different variants of the SPT and SDL influenced the resulting score. Although these findings do not alter the administration or scoring of the OPAT, they do provide a valuable reference in the event of future inquiries regarding the development of the OPAT., (Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2021. This work is written by (a) US Government employee(s) and is in the public domain in the US.)

Abstract: Spiering, BA, Walker, LA, Larcom, K, Frykman, PN, Allison, SC, and Sharp, MA. Predicting soldier task performance from physical fitness tests: reliability and construct validity of a soldier task test battery. J Strength Cond Res 35(10): 2749-2755, 2021-The purpose of this study was to determine the reliability and construct validity of a battery of tests designed to assess soldier task performance. In the first part of the study (designed to assess test-retest reliability), 33 enlisted soldiers (31 men, 2 women; 23 ± 3 years; 1.75 ± 0.08 m; and 81.4 ± 12.8 kg) completed a 4-event "soldier task test battery" (STTB) on 4 occasions, each separated by at least 1 week. The STTB consisted of the following tests, in order: (a) 30-m grenade throw for accuracy; (b) running long jump while wearing a 20.5-kg load; (c) 1 repetition maximum box lift; and (d) 3.2-km load carriage time trial while wearing a 33-kg load. In the second part of the study (designed to assess construct validity), 41 male soldiers (22 ± 3 years; 1.75 ± 0.08 m; and 81.4 ± 12.9 kg) completed the STTB and a series of physical fitness tests. The physical fitness tests included measurements of body composition, muscular strength, muscular power, muscular endurance, and cardiovascular endurance. Overall performance on the STTB (reflected by the sum of z-scores across individual tests) demonstrated an intraclass correlation coefficient of 0.95 and was correlated to lean mass, V˙o2peak, and measures of muscular strength and power. Lean body mass and standing long jump predicted performance on the STTB (R2 = 0.41). In conclusion, this STTB can reliably assess performance of soldiering tasks. The relationships between the STTB and physical fitness tests can be used to develop training programs to prepare soldiers to perform physically demanding tasks., (Copyright © 2019 National Strength and Conditioning Association.)

Introduction: Limited work comparing the effect of heavier carried loads (greater than 30 kg) between men and women has attributed observed differences to sex with the possibility that anthropometric differences may have contributed to those discrepancies. With the recent decision permitting women to enter Combat Arms roles, knowledge of sex-based differences in gait response to load carriage is more operationally relevant, as military loads are absolute and not relative to body weight. The purpose of this study was to describe differences in gait parameters at light to heavy loads between anthropometrically similar male and female soldiers., Materials and Methods: Eight female and 8 male soldiers, frequency-matched (1-to-1) on height (±0.54 cm) and mass (±0.52 kg), walked at 1.34 m∙s-1 for 10-min bouts on a level treadmill while unloaded (BM) and then carrying randomized vest-borne loads of 15, 35, and 55 kg. Spatiotemporal and kinematic data were collected for 30 s after 5 min. Two-way repeated measures analyses of variance were conducted to compare the gait parameter variables between sexes at each load., Results: As load increased, overall, the percent double support increased, step frequency increased, stride length decreased, hip and ankle range of motion (ROM) increased, and vertical center of mass (COM) displacement increased. Sex-based significant differences were observed in knee ROM and mediolateral COM displacement. Among the male participants, knee ROM increased significantly for all loads greater than BM. For mediolateral COM displacement, male remained constant as load increased, whereas female values decreased between BM and 35 kg., Conclusions: Spatiotemporal and kinematic differences in gait parameters were primarily because of increases in load magnitude. The observed sex-related differences with increasing loads suggest that women may require a more stable gait to support the additional load carried., (Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2020. This work is written by (a) US Government employee(s) and is in the public domain in the US.)

Introduction: This study compared the relationship between height (HT), body mass (BM), and body mass index (BMI) of female trainees and active duty female soldiers and their performance on simulated common soldiering tasks (CSTs) with high physical demands., Methods: Female trainees (n = 133) and soldiers (n = 229) completed the following CSTs: sandbag carry, move under fire, casualty drag, casualty evacuation, and road march. Quartiles were created among HT, BM, and BMI by which task performance was compared using ANOVAs with Tukey post hoc comparisons., Results: For both trainees and soldiers, HT, BM, and BMI were positively associated with improved road march, casualty drag, casualty evacuation, and sandbag carry performance. On the move under fire task, only soldier HT was positively associated with improved performance., Conclusion: Female trainees and soldiers who are taller and heavier with a higher BMI may demonstrate better performance on CSTs required of all soldiers. In addition to task-specific training, performance of CSTs may be enhanced in tasks requiring strength and power by recruiting and retaining taller and heavier females with a higher BMIs. Allowances should be considered for soldiers and trainees who can successfully perform soldiering tasks with high physical demands despite less desirable anthropometric measurements., (© The Author(s) 2020. Published by Oxford University Press on behalf of All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Canino, MC, Foulis, SA, Zambraski, EJ, Cohen, BS, Redmond, JE, Hauret, KG, Frykman, PN, and Sharp, MA. U.S. Army Physical Demands Study: Differences in physical fitness and occupational task performance between trainees and active duty soldiers. J Strength Cond Res 33(7): 1864-1870, 2019-U.S. Army initial entry training (IET) is designed to prepare trainees for the military environment and subsequent training, including specific programs to increase physical fitness to perform job-specific tasks to the minimal acceptable performance standard (MAPS). The aim of this study was to compare physical fitness and occupational task performance of trainees at the end of IET to that of active duty soldiers. One hundred seventy-nine male combat arms trainees at the end of IET and 337 male combat arms active duty soldiers performed a sandbag carry (SBC), casualty drag (CD), and move under direct fire (MUF). Physical fitness was assessed using Army Physical Fitness Test scores. A questionnaire was administered to determine frequency of task performance. Active duty soldiers compared with trainees were older (p < 0.01) and performed more push-ups (p < 0.01) and sit-ups (p < 0.01). Trainees performed the 2-mile run faster (p < 0.01). Ninety-four percent of trainees and 99% of active duty soldiers performed the 3 tasks to the MAPSs. Active duty soldiers performed significantly faster on both the SBC (p < 0.01) and CD (p < 0.01) and reported a higher task frequency on the SBC (p = 0.03) and CD (p < 0.01). No difference in MUF performance (p = 0.16) and task frequency (p = 0.13) was detected. Initial entry training seems to provide sufficient physical training as most trainees were able to meet the MAPSs; however, performance differences were still apparent between trainees and active duty soldiers. Additional practice performing the physically demanding tasks may help maximize performance on the physically demanding job requirements.

Foulis, SA, Redmond, JE, Frykman, PN, Warr, BJ, Zambraski, EJ, and Sharp, MA. U.S. Army physical demands study: reliability of simulations of physically demanding tasks performed by combat arms soldiers. J Strength Cond Res 31(12): 3245-3252, 2017-Recently, the U.S. Army has mandated that soldiers must successfully complete the physically demanding tasks of their job to graduate from their Initial Military Training. Evaluating individual soldiers in the field is difficult; however, simulations of these tasks may aid in the assessment of soldiers' abilities. The purpose of this study was to determine the reliability of simulated physical soldiering tasks relevant to combat arms soldiers. Three cohorts of ∼50 soldiers repeated a subset of 8 simulated tasks 4 times over 2 weeks. Simulations included: sandbag carry, casualty drag, and casualty evacuation from a vehicle turret, move under direct fire, stow ammunition on a tank, load the main gun of a tank, transferring ammunition with a field artillery supply vehicle, and a 4-mile foot march. Reliability was assessed using intraclass correlation coefficients (ICCs), standard errors of measurement (SEMs), and 95% limits of agreement. Performance of the casualty drag and foot march did not improve across trials (p > 0.05), whereas improvements, suggestive of learning effects, were observed on the remaining 6 tasks (p ≤ 0.05). The ICCs ranged from 0.76 to 0.96, and the SEMs ranged from 3 to 16% of the mean. These 8 simulated tasks show high reliability. Given proper practice, they are suitable for evaluating the ability of Combat Arms Soldiers to complete the physical requirements of their jobs.

Objectives: The United States Army sought to create a legally defensible, scientifically validated physical pre-employment screening test. The purpose of this study was to identify a single combination of predictor tests that would predict physical performance on all of the criterion measure task simulations relevant to the Combat Arms military occupational specialties., Design: Concurrent validation., Methods: Data from 838 (608 males, 230 females) soldiers who completed both the criterion measure task simulations of a military occupational specialty and up to 14 predictor tests were used in the development of the test batteries. Stepwise regressions were used to identify test batteries that significantly predicted performance on the criterion measure task simulations of the military occupational specialties., Results: Three test batteries were developed based on different subsets of the predictor tests: Test Battery 1 consisted of the medicine ball put, squat lift, beep test, standing long jump, and arm ergometer (adjusted R 2 =0.80-0.85, p<0.01); Test Battery 2 consisted of the medicine ball put, squat lift, beep test, and standing long jump (adjusted R 2 =0.79-0.80, p<0.01); and Test Battery 3 consisted of the standing long jump, 1-minute push-ups, 1-minute sit-ups, 300m sprint, and Illinois agility test (adjusted R 2 =0.55-0.71, p<0.01)., Conclusions: Test Battery 2 was selected as the Army's Occupational Physical Assessment Test. It was highly predictive of performance of the Combat Arms military occupational specialties, required no complex equipment, and covered a range of physical fitness domains., (Published by Elsevier Ltd.)

The U.S. Armed Forces have recently approved full integration of women into combat roles. Physical fitness demands for executing Military Occupational Specialties (MOS) are substantial; thus lifting and load carriage capability improvements are desirable., Objectives: To determine if a specially-designed physical conditioning program could lessen the gap between the performance of male and female Soldiers in lifting and load carriage and thereby enable women to meet the requirements of most, if not all, Army MOSs., Methods: Forty women participated in a 24-week physical training program, which included resistance training, long-distance running, backpacking, and specialized drills. Pre- and post-tests of occupational and physical performance measures were conducted before and after training. Repeated measures analysis of variance were used to determine statistically significant differences among the pre-, mid- and posttests., Results: Women increased maximal occupational lifting strength 12-20 kg, added 9-34 repetitions in lifting endurance, increased 0.23 m in jumping performance, added 46 repetitions in local muscular endurance, and decreased load carriage for time by 3.7-8.6 min. Women scored within 82-94% of untrained male scores for aerobic capacity and muscular endurance after training., Conclusion: Women's ability to perform physically-demanding military occupational tasks was significantly improved following 6 months of concurrent training, with emphasis on load carriage and lifting. The percentage of women that qualified for current "heavy" and "very heavy" MOSs was initially 24%, but increased to 78% after training. A resistance training program of 6+ months can adequately prepare women for "heavy" to "very heavy" MOS's., (Copyright © 2017 Sports Medicine Australia. All rights reserved.)

Objectives: Characterize the distribution of foot-strike (FS) patterns in U.S. Army Soldiers and determine if FS patterns are related to self-reported running injuries and performance., Methods: 341 male Soldiers from a U.S. Army Combined Arms Battalion ran at their training pace for 100 meters, and FSs were recorded in the sagittal plane. Participants also completed a survey related to training habits, injury history, and run times. Two researchers classified FS patterns as heel strike (HS) or nonheel strike (NHS, combination of midfoot strike and forefoot strike patterns). Two clinicians classified the musculoskeletal injuries as acute or overuse. The relationship of FS type with two-mile run time and running-related injury was analyzed (p ≤ 0.05)., Results: The Soldiers predominately landed with an HS (87%) and only 13% were characterized as NHS. Running-related injury was similar between HS (50.3%) and NHS (55.6%) patterns (p = 0.51). There was no difference (p = 0.14) between overuse injury rates between an HS pattern (31.8%) and an NHS pattern (31.0%). Two-mile run times were also similar, with both groups averaging 14:48 minutes., Conclusion: Soldiers were mostly heel strikers (87%) in this U.S. Army Combined Arms Battalion. Neither FS pattern was advantageous for increased performance or decreased incidence of running-related injury., (Reprint & Copyright © 2015 Association of Military Surgeons of the U.S.)

During group marches, soldiers must walk in step with one another at the same imposed cadence. The literature suggests that shorter trainees may be more susceptible to injury due to overstriding that can occur when taller recruits dictate marching cadence. This study assessed the effects of fixed cadence simulated marching at cadences above and below preferred step rate (PSR) on lower extremity joint mechanics in individuals who were unaccustomed to marching. During three separate visits, 13 volunteers walked with a 20 kg load on a force-sensing treadmill at self-selected PSR, PSR+15% (shorter strides), and PSR-15% (longer strides) at 1.3 m/s for 60 min. Two-way RM ANOVAs (cadence by time) were performed during the stance phase. Ranges of motion and anteroposterior ground reaction force increased significantly as cadence decreased (P < .03). Knee extension moment increased slightly when step rate decreased from PSR+15% (shortest strides, 0.85 ± 0.2 N m/kg) to PSR (0.87 ± 0.3 N m/kg, 3% increase); however, this increase was substantially greater (20% increase) when cadence was decreased from PSR to PSR-15% (longest strides, 1.09 ± 0.3 N m/kg). Our results indicate that overstriding during fixed-cadence marching is a factor that can substantially increase mechanical stress on lower extremity joints.

The dose-response relationship between biomechanical variables and the magnitude of external loads is unclear. The use of different load distributions (e.g., pack types) may confound results because of changes in torso center of mass. Therefore, we examined the relationship between load magnitude and sagittal plane lower extremity mechanics of Soldiers walking with two symmetrically distributed loads. Fourteen Soldiers marched on a force-sensing treadmill at 1.34 m/s for 10 minutes with no load (BW&#95;00) and while wearing vest-borne loads of 15 kg (BW&#95;15) and 55 kg (BW&#95;55). The effects of the loads on sagittal plane joint angles and moments were compared using 1-way repeated measures analyses of variance. Compared with BW&#95;00, knee extension moment increased with the 15- and the 55-kg loads (both p < 0.003), confirming previously reported load-related biomechanical responses. Knee moment increases during early stance appeared to be the primary means by which the lower extremity counteracted BW&#95;15 during early stance; in contrast, hip extensors and ankle dorsiflexors appeared to be the primary muscular efforts responsible for propulsion during late stance. Findings elucidated the effects of load magnitude on lower extremity mechanics without postural changes that result from pack-related shifts in torso center of mass., (Reprint & Copyright © 2014 Association of Military Surgeons of the U.S.)

This study compared three-dimensional trunk and pelvis range of motion (ROM) during a sustained asymmetric box lift/lower task between a group with a history of low back pain (HBP, n = 9) and a group with no history of low back pain (NBP, n = 9). Participants lifted an 11-kg box for 10 min at 12 cycles/min from ankle height in front to shelves 45 deg off-centre at waist height. Kinematic data were collected at the beginning (min1), middle (min5) and end of the bout (min9). Two-way analyses of variance were performed for all variables. Pelvis and trunk transverse ROM were similar at min1. By min9, HBP group did not change (31.9 ± 9 deg); however, ROM decreased in NBP group (21.6 ± 6 deg, p < 0.05). Therefore, despite no current pain, the HBP group demonstrated protective lifting mechanics compared to controls. Also discussed are implications for studying lifting paradigms at sub-maximal effort over longer periods of time., Practitioner Summary: Differences between groups over time demonstrate residual consequences of low back pain (LBP) in a manual materials handling scenario. Individuals with a history of LBP (pain free for 6 months) demonstrated more conservative lifting mechanics towards the end of the bout compared to controls with no history of LBP.

Studies of exhaustive exercise on marksmanship are inconclusive and have not measured trigger pull latencies (LAT) nor considered impact of added torso loads. This study examined the impact of exhaustive whole-body exercise and torso loading on accuracy, precision, and latency during a marksmanship test. Twelve men lifted a 20.5-kg box on to a 1.55-m high shelf until they could not maintain a 12 lifts·min⁻¹ pace. Within 25 seconds of ending the lifting task, the subjects started a 10-minute rifle marksmanship test (8 shots·min⁻¹). During lifting and shooting, the subjects wore 2 different loads: NOLOAD = boots, uniform, and helmet (5.9 kg) and LOAD = a torso-borne load (29.9 kg) + NOLOAD. With the LOAD, the subjects were only able to work for 69% as long, perform 31% as many lifts, or do 38% as much total work compared with the NOLOAD condition. Despite performing less total external work during LOAD, the heart rate (HR) was more than 25% higher than NOLOAD. Measures of accuracy and precision improved and stabilized after minute 3. Overall, LAT increased (p < 0.025) for LOAD (mean ± SE, 2,522 ± 81 milliseconds), compared with NOLOAD (2,240 ± 121). During 0-4 minutes, LAT for LOAD was 14% greater than for NOLOAD (p < 0.05); from 4 to 10 minutes, LAT did not differ. Exhaustive whole-body exercise transiently degraded accuracy regardless of load. In the LOAD condition, LAT was immediately increased and sustained for 10 minutes; in the NOLOAD condition, LAT increased gradually. Although load did not decrease accuracy, it increased the time to engage targets, which can impact fighting effectiveness and survivability.

This study examined vertical jump performance using a force platform and weighted vest to determine why hypohydration (approximately 4% body mass) does not improve jump height. Measures of functional performance from a force platform were determined for 15 healthy and active males when euhydrated (EUH), hypohydrated (HYP) and hypohydrated while wearing a weighted vest (HYP(v)) adjusted to precisely match water mass losses. HYP produced a significant loss of body mass [-3.2 +/- 0.5 kg (-3.8 +/- 0.6%); P < 0.05], but body mass in HYP(v) was not different from EUH. There were no differences in absolute or relative peak force or power among trials. Jump height was not different between EUH (0.380 +/- 0.048 m) and HYP (0.384 +/- 0.050 m), but was 4% lower (P < 0.05) in HYP(v) (0.365 +/- 0.52 m) than EUH due to a lower jump velocity between HYP(v) and EUH only (P < 0.05). However, vertical ground reaction impulse (VGRI) was reduced in both HYP and HYP(v) (2-3%) compared with EUH (P < 0.05). In conclusion, this study demonstrates the failure to improve jump height when HYP can be explained by offsetting reductions in both VGRI and body mass.

Predictive models of battlefield physical performance can benefit the military. To develop models, 32 physically trained men (mean +/- SD: 28.0 +/- 4.7 years, 82.1 +/- 11.3 kg, 176.3 +/- 7.5 cm) underwent (1) anthropometric measures: height and body mass; (2) fitness tests: push-ups, sit-ups, 3.2-km run, vertical jump, horizontal jump; (3) simulated battlefield physical performance in fighting load: five 30-m sprints prone to prone, 400-m run, obstacle course, and casualty recovery. Although greater body mass was positively associated with better casualty recovery performance, it showed trends toward poorer performance on all the other fitness and military performance tests. Regression equations well predicted the simulated battlefield performance from the anthropometric measures and physical fitness tests (r = 0.77-0.82). The vertical jump entered all four prediction equations and the horizontal jump entered one of them. The equations, using input from easy to administer tests, effectively predict simulated battlefield physical performance.

A sensitive, reliable, field-expedient test may be valuable for monitoring interventions during periods of anticipated physical performance decline. The purpose of this study was to determine the capabilities of unloaded jumping tests for detecting decrements in physical performance following eight days of military sustained operations. Twenty-nine U. S. Marines (24 +/- 1 y; 180 +/- 6 cm; 82.5 +/- 8.2 kg) performed 1, 5 and 30 repetition(s) of unloaded countermovement jumps (UJ) before and after eight days of sustained operations (SUSOPS). Jump performance data was collected simultaneously using a switch mat (SM) and a linear position transducer (LPT). Jump height (m) and power (W) were highest using 1 UJ and declined 4.9 and 8.9%, respectively after SUSOPS. Jump power (JP) declined progressively over 30 UJ (20%). Five UJ offered no advantages over 1 UJ and was inadequate to examine changes in muscle fatigability (pre: 1294 +/- 138 W; post: 1250 +/- 165 W). The SM and a LPT were in agreement and had a high correlation (r = 0.92). One UJ was a sensitive, easy to implement test for monitoring the collective impact of high physical, nutritional, cognitive, and environmental stress on an individuals' physical performance before and after 8 days of SUSOPS, suggesting decrements in physical performance associated with overreaching can be detected by simply administered field-expedient jumping tests.

Objective: Prolonged physical exertion with inadequate time for recuperation may result in an overtraining phenomenon characterized by reduced physical strength and endurance capacity. We tested the hypothesis that highly motivated men pushed to the limits of their endurance capacity for 3 months would suffer physical breakdown characterized by loss of lean mass and reduced physical performance capacity., Methods: Two well-trained men (VO2max > 60 mL/kg/min), aged 25 years, completed an unsupported, 2928-km, south-to-north ski trek across Greenland in 86 days. The trek involved ski marching, typically for 9 h/d, pulling sleds initially containing 150 kg and a high-fat (60%) energy-dense diet of 25.1 MJ/d. Body composition and physical performance data were collected 14 days before and 4 days after the trek., Results: Energy expenditure based on doubly labeled water during three 2-week periods ranged from 28.3 and 34.6 MJ/d in rugged terrain to 14.6 and 16.1 MJ/d during travel on flat terrain for subjects 1 and 2, respectively. Both men lost weight, completing the trek with low-normal fat stores (approximately 13% body fat). The lighter man gained 0.6 kg lean mass, while the heavier man lost 1.4 kg lean mass and a larger amount of fat weight (7.0 kg). Most performance measures showed trivial changes within the errors of measurement and test reproducibility, indicating no loss of endurance capacity, but anaerobic tests (Wingate and vertical jump) were markedly reduced. Markers of metabolic status, including oral glucose tolerance tests, indicated no functional impairments., Conclusions: Although the number of subjects was limited, this observational study demonstrated that well-trained and experienced long-distance ski trekkers who eat an adequate high-calorie diet can perform endurance treks in severe cold, with little or no loss of lean mass and physical capability.

Objective: An Arctic expedition provided an opportunity to examine the interaction between cold injury and peripheral acclimatization. The conditions were similar to those during which acclimatization has been demonstrated, yet they were also conducive to development of peripheral cold injury., Methods: Extremity digit temperatures were measured during 30-minute peripheral cold-water (4 degrees C) immersion (CWI) in 2 explorers (R.G. and T.L.) before and after a 109-day Arctic ski trek (average T(air) = -21 degrees C). This self-supported trek involved carrying heavy backpacks (up to 45 kg) and hauling sleds (approximately 100 kg)., Results: During the expedition, the explorers' hands did not sustain frostbite, but their feet developed moderate trench foot. Unexpectedly, both men exhibited lower mean finger temperatures during CWI after the expedition in right and left hands (R.G. by 0.9 degrees C and 0.2 degrees C; T.L. by 1.8 degrees C and 1.1 degrees C), suggesting peripheral acclimatization was impaired. In contrast, mean toe temperatures during CWI were warmer in both right and left feet for T.L. (by 3.6 degrees C and 2.3 degrees C) and in the left foot for R.G. (by 1.3 degrees C) postexpedition. There was no change in R.G.'s right toe mean temperature., Conclusions: We speculate that prolonged heavy load carriage may have impaired blood flow or nerve conduction in the hands and inhibited acclimatization. Our data also suggest that despite incidence of moderate trench foot, acclimatization can still occur after resolving this injury.

To determine the number of test sessions needed to stabilize performance on two military occupational physical tests and to assess their reliability, 10 male soldiers (22 +/- 3 yrs, 183 +/- 7 cm, 87 +/- 8 kg) performed both an indoor 6-station obstacle course (OC) and a repetitive box-lifting task (RBLT). The OC consisted of 46 cm-high hurdles, zigzag sprint, low crawl, horizontal pipe shimmy, 1.4 m wall traversal, and straight sprint. The RBLT required subjects to lift 20.5 kg boxes, continuously for 10 minutes, from the ground onto 1.3 m high platforms positioned 2.4 m apart. The OC mean +/- SD times (s), for sessions 1-4 respectively, were 37.4 +/- 2.2, 35.8 +/- 2.5, 34.7 +/- 2.1, and 34.5 +/- 1.7 seconds. The number of boxes lifted was 177 +/- 31, 194 +/- 28, 189 +/- 32, and 186 +/- 37 for the RBLT. Performance stabilized on the 3rd session for the OC (7% improvement over first trial, p < 0.05) and on the 2nd session for the RBLT (9% improvement over first trial, p < 0.05). The intraclass correlation coefficients were 0.92 and 0.94 for the OC and RBLT, respectively. This study demonstrates that both are reliable tests, but they do require administration of 1 single-trial session of RBLT and 2 two-trial sessions of OC before highly reliable performance data are obtained.

Forty-five women participated in a 24-week physical training program designed to improve lifting, load carriage, and running performance. Activities included weightlifting, running, backpacking, lift and carry drills, and sprint running. Physicians documented by passive surveillance all training-related injuries. Thirty-two women successfully completed training program. Twenty-two women (48.9%) suffered least 1 injury during training, but only 2 women had to drop out of the study because of injuries. The rate of injury associated with lost training time was 2.8 injuries per 1,000 training hours of exposure. Total clinic visits and days lost from training were 89 and 69, respectively. Most injuries were the overuse type involving the lower back, knees, and feet. Weightlifting accounted for a majority of the lost training days. A combined strength training and running program resulted in significant performance gains in women. Only 2 out of 45 participants left the training program cause of injuries.

Data are lacking regarding regional morphological changes among women after prolonged physical training. This study employed dual-energy X-ray absorptiometry to assess changes in whole body and regional (i.e., trunk, legs, arms) fat mass, lean mass, and bone mineral content body composition adaptations in 31 healthy women pre-, mid-, and post-6 mo of periodized physical training. These results were compared with those of 1) a control group of women who had not undergone the training program and were assessed pre- and post-6 mo and 2) a group of 18 men that was tested only once. Additionally, magnetic resonance imaging was used to assess changes in muscle morphology of the thigh in a subset of 11 members of the training group. Physical training consisted of a combination of aerobic and resistance exercise in which the subjects engaged for 5 days/wk for 24 wk. Overall, the training group experienced a 2.2% decrease, a 10% decrease, and a 2.2% increase for body mass, fat mass, and soft tissue lean mass, respectively. No changes in bone mineral content were detected. The women had less of their soft tissue lean mass distributed in their arms than did the men, both before and after the women were trained. Novel to this study were the striking differences in the responses in the tissue composition of the arms (31% loss in fat mass but no change in lean mass) compared with the legs (5.5% gain in lean mass but no change in fat mass). There was a 12% fat loss in the trunk with no change in soft tissue lean mass. Dual-energy X-ray absorptiometry and magnetic resonance imaging fat mass measurements showed good agreement (r = 0. 72-0.92); their lean mass measurements were similar as well, showing approximately 5.5% increases in leg lean tissue. These findings show the importance of considering regional body composition changes, rather than whole body changes alone when assessing the effects of a periodized physical training program.

The purpose of this study was to investigate the acute responses of both stress and fluid regulatory hormones to a single bout of resistance exercise in both trained and untrained men. Seven competitive power lifters (PL) and 12 untrained subjects (UT) performed one set of the leg press exercise to exhaustion at 80% of their respective one-repetition maximum. Blood samples were obtained twice prior to exercise (at P1 and P2), immediately postexercise (IP), and at 5 minutes postexercise (5PE). Compared to P1 and P2, plasma epinephrine, norepinephrine, dopamine, atrial peptide, osmolality, and blood lactic acid increased significantly (p < or = 0.05) at IP. Plasma epinephrine, norepinephrine, atrial peptide, and blood lactic acid concentrations remained elevated at 5PE compared to P1 and P2. Plasma renin activity and angiotensin II were significantly elevated at 5PE compared to P1, P2, and IP, and this increase was significantly greater in PL compared to UT at 5PE. These data indicate that an acute bout of resistance exercise dramatically affects secretion of stress and fluid regulatory hormones.

Previous studies have demonstrated that full recovery from weight loss may take months or years. The present investigation examined short-term recovery (5 wks "post") of physical performance (muscular strength, muscular power, vertical jump), body composition, metabolic hormones (testosterone, luteinizing hormone, sex hormone binding globulin, insulin-like growth factor-1, triiodothyronine, thyroxine, thyroid binding globulin, and thyroid-stimulating hormone) and metabolic markers (transferrin, ferritin, prealbumin, glycerol, nonesterified fatty acids, high-density lipoproteins, and lactate) in 10 healthy young men after an 8-week Army course with an energy deficit (1000 kcal/d) and loss of body mass (-12%). Subjects ate ad libitum after the course ended ("post"). Body composition was determined by dual-energy X-ray absorptiometry; strength from a simulated power clean, power from body mass and jump height, and metabolic hormones were measured in morning-fasted blood by radioimmunoassay. With the exception of transferrin and glycerol, all study parameters were significantly (p<.05) altered by the training course. At 5 weeks post fat-free mass along with all physical performance measures returned to initial levels; however, fat mass had significantly (p<.05) increased over initial levels. Also, with the exception of lactate, all measured hormones and markers were close to initial levels and within normal ranges. Reported complications during recovery included sleep irregularities, diarrhea, loss of motivation and feelings of fatigue. While the long range effect of this energy deprivation experience is uncertain, these data do suggest that severe weight loss does not result in lasting alterations of the contractile and metabolic properties of skeletal muscle in young, lean, healthy men.

Using an exercise device that integrates maximal voluntary static contraction (MVC) of knee extensor muscles with dynamic knee extension, we compared progressive muscle fatigue, i.e., rate of decline in force-generating capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr). Eight healthy men performed exhaustive constant work rate knee extension (21 +/- 3 W, 79 +/- 2 and 87 +/- 2% of 1-leg knee extension O2 peak uptake for normoxia and hypobaria, respectively) from knee angles of 90-150 degrees at a rate of 1 Hz. MVC (90 degrees knee angle) was performed before dynamic exercise and during < or = 5-s pauses every 2 min of dynamic exercise. MVC force was 578 +/- 29 N in normoxia and 569 +/- 29 N in hypobaria before exercise and fell, at exhaustion, to similar levels (265 +/- 10 and 284 +/- 20 N for normoxia and hypobaria, respectively; P > 0.05) that were higher (P < 0.01) than peak force of constant work rate knee extension (98 +/- 10 N, 18 +/- 3% of MVC). Time to exhaustion was 56% shorter for hypobaria than for normoxia (19 +/- 5 vs. 43 +/- 7 min, respectively; P < 0.01), and rate of right leg MVC fall was nearly twofold greater for hypobaria than for normoxia (mean slope = -22.3 vs. -11.9 N/min, respectively; P < 0.05). With increasing duration of dynamic exercise for normoxia and hypobaria, integrated electromyographic activity during MVC fell progressively with MVC force, implying attenuated maximal muscle excitation. Exhaustion, per se, was postulated to related more closely to impaired shortening velocity than to failure of force-generating capacity.

There is virtually no published information on muscle fatigue, defined as a gradual decline in force-generating capacity, during conventional dynamic (D) leg exercise. To quantitate progression of fatigue, we developed 1) a model featuring integration of maximal voluntary static contraction (MVC) of knee extension (KE) muscles with ongoing DKE and 2) a device that allows frequent rapid transfer between DKE isolated to the quadriceps femoris muscles and measurement of KE MVC. Eight healthy men performed graded and submaximal constant work rate one-leg DKE to exhaustion while seated. Work rate, a product of a contraction rate (1 Hz), force measured at the ankle, and distance of ankle movement from 90 degrees to 150 degrees of KE, was precisely controlled. Lack of rise in myoelectric activity in biceps femoris of the active leg during DKE and MVC was consistent with restriction of muscle action to quadriceps femoris. The slope of the linear relationship between O2 uptake and work rate was 13.7 ml O2/W (r = 0.93). This slope and the increase of heart rate relative to increasing work intensity agreed with published values for D leg exercise. Test-retest values for O2 uptake were similar (P > 0.05) for matched DKE work rates. To track fatigue, MVC (90 degrees knee angle) was performed every 2 min of DKE. After 4 min of DKE at work rates corresponding to (mean +/- SE) 66 +/- 2, 78 +/- 2, and 100% of peak DKE O2 uptake, MVC fell to 95 +/- 3, 90 +/- 5, and 65 +/- 7%* of MVC of rested muscle, respectively (*P < 0.01 from previous work rates). Virtually identical declines in MVC were observed by the end of graded work rate DKE and submaximal constant work rate DKE tests. Quantitation of progressive muscle fatigue during D leg exercise provides a framework to study the effects of a variety of interventions on the fatigue process and may permit unique insights into the involved mechanisms.

Isometric maximal handgrip strength (GSmax) has been used as an expedient test of overall muscle strength and index of fat-free mass (FFM). We tested this relationship in 55 fit young men undergoing high rates of FFM loss in an 8.5-wk military training course involving multiple stressors including nutritionally uncomplicated energy deficit. GSmax was measured by a hand dynamometer interfaced with a computer providing visual feedback; another strength test, measuring dynamic strength of larger muscle groups (Cleansim), was also performed. GSmax did not change (530 +/- 57 vs 529 +/- 63 N) in the face of a 15.6% loss of body weight (12.1 +/- 3.4 (SD) kg), including 6.9% loss of FFM (4.6 +/- 2.6 kg), but Cleansim decremented significantly (77.4 +/- 9.6 to 58.7 +/- 8.9 kg) and changes were significantly correlated with delta FFM for GSmax (r = 0.31) and Cleansim (r = 0.49). We conclude that GSmax is not a good representation of changes in total FFM in healthy young men even though it appears to be useful in more severely catabolic patients with extreme losses of FFM and in pubertal boys making large gains in FFM. Other aspects of physical performance are clearly affected by high rates of weight loss, as demonstrated by decrements in the Cleansim and its stronger relationship to delta FFM.

Nine eumenorrheic women (age 24.11 +/- 4.28 yr) performed each of six randomly assigned heavy-resistance protocols (HREPs) on separate days during the early follicular phase of the menstrual cycle. The HREPs consisted of two series [series 1 (strength, S) and series 2 (hypertrophy, H)] of three protocols, each using identically ordered exercises controlled for load [5 vs. 10 repetitions maximum (RM)], rest period length (1 vs. 3 min), and total work (J) within each three-protocol series. Blood measures were determined pre-, mid- (after 4 of 8 exercises), and postexercise (0, 5, 15, 30, 60, 90, 120 min and 24 and 48 h). In series 1, a significant (P < 0.05) reduction in growth hormone (GH) was observed at 90 min postexercise for all three protocols. In series 2, the 10-RM protocol with 1-min rest periods (H10/1) produced significant increases above rest in GH concentrations at 0, 5, and 15 min postexercise, and the H10/1 and H5/1 protocols demonstrated significant reductions at 90 and 120 min postexercise. Cortisol demonstrated significant increases in response to the S10/3 protocol at 0 min, to the H10/1 protocol at midexercise and at 0 and 5 min postexercise, and to the H5/1 protocol at 5 and 15 min postexercise. No significant changes were observed in total insulin-like growth factor I, total testosterone, urea, or creatinine for any of the HREPs. Significant elevations in whole blood lactate and ammonia along with significant reductions in blood glucose were observed. Hormonal and metabolic blood variables measured in the early follicular phase of the menstrual cycle varied in response to different HREPs. The most dramatic increases above resting concentrations were observed with the H10/1 protocol, indicating that the more glycolytic HREPs may stimulate greater GH and cortisol increases.

It is widely acknowledged that musculoskeletal injuries occur as a result of vigorous physical activity and exercise, but little quantitative documentation exists on the incidence of or risk factors for these injuries. This study was conducted to assess the incidence, types, and risk factors for training-related injuries among young men undergoing Army infantry basic training. Prior to training we evaluated 303 men (median age 19 yr), utilizing questionnaires and measurements of physical fitness. Subjects were followed over 12 wk of training. Physical training was documented on a daily basis, and injuries were ascertained by review of medical records for every trainee. We performed univariate and multivariate analyses of the data. Cumulative incidence of subjects with one or more lower extremity training-related injury was 37% (80% of all injuries). The most common injuries were muscle strains, sprains, and overuse knee conditions. A number of risk factors were identified, including: older age, smoking, previous injury (sprained ankles), low levels of previous occupational and physical activity, low frequency of running before entry into the Army, flexibility (both high and low), low physical fitness on entry, and unit training (high running mileage).

To examine the changes of plasma beta-endorphin (beta-EP) concentrations in response to various heavy-resistance exercise protocols, eight healthy male subjects randomly performed each of six heavy-resistance exercise protocols, which consisted of identically ordered exercises carefully designed to control for the repetition maximum (RM) resistance (5 vs. 10 RM), rest period length (1 vs. 3 min), and total work (joules). Plasma beta-EP, ammonia, whole blood lactate and serum cortisol, creatine kinase, urea, and creatinine were determined preexercise, midexercise, immediately postexercise, and at various time points after the exercise session (5 min-48 h), depending on the specific blood variable examined. Only the high total work-exercise protocol [1 min rest, 10 RM load (H10/1)] demonstrated significant increases in plasma beta-EP and serum cortisol at midexercise and 0, 5, and 15 min postexercise. Increases in lactate were observed after all protocols, but the largest increases were observed after the H10/1 protocol. Within the H10/1 protocol, lactate concentrations were correlated (r = 0.82, P < 0.05) with plasma beta-EP concentrations. Cortisol increases were significantly correlated (r = 0.84) with 24-h peak creatine kinase values. The primary finding of this investigation was that beta-EP responds differently to various heavy-resistance exercise protocols. In heavy-resistance exercise, it appears that the duration of the force production and the length of the rest periods between sets are key exercise variables that influence increases in plasma beta-EP and serum cortisol concentrations. Furthermore the H10/1 protocol's significant challenge to the acid-base status of the blood, due to marked increases in whole blood lactate, may be associated with mechanisms modulating peripheral blood concentrations of beta-EP and cortisol.

Plasma proenkephalin peptide F immunoreactivity and catecholamines were examined on separate days in nine healthy males before and after maximal exercise to exhaustion at four intensities [36, 55, 73, and 100% of maximal leg power (MLP)] by use of a computerized cycle ergometer. The mean duration of 36, 55, 73, and 100% MLP was 3.31, 0.781, 0.270, and 0.1 min, respectively. All intensities were greater than those eliciting peak O2 uptake for the individual subjects. Blood samples were obtained before, immediately after exercise, and 5 and 15 min after exercise. Significant (P less than 0.05) increases in plasma peptide F immunoreactivity (i.e., from mean resting value of 0.18 to 0.43 pmol/ml) were observed immediately after exercise at 36% MLP. Significant increases in plasma epinephrine were observed immediately after exercise at 36% MLP (i.e., from mean resting value of 2.22 to 3.11 pmol/ml) and 55% MLP (i.e., from mean resting value of 1.67 to 2.98 pmol/ml) and 15 min after exercise at 100% MLP (i.e., from mean resting value of 1.92 to 3.88 pmol/ml). Significant increases for plasma norepinephrine were observed immediately after exercise (36, 55, 73, and 100% MLP), 5 min after exercise (36, 55, and 73% MLP), and 15 min after exercise (36% MLP). Increases in whole blood lactate were observed at all points after exercise for 36, 55, and 73% MLP and 5 min after exercise for 100% MLP. These data show that brief high-intensity exercise results in differential response patterns of catecholamines and proenkephalin peptide F immunoreactivity.

Countermovement and arm-swing characterize most jumping. For determination of their effects and interaction, 18 males jumped for maximal height from a force platform in all four combinations of arm-swing/no-arm-swing and countermovement/no-countermovement. For all jumps, vertical velocity peaked 0.03 s before and dropped 6-7% by takeoff. Peak positive power averaged over 3,000 W, and occurred about 0.07 s before takeoff, shortly after peak vertical ground reaction force (VGRF) and just before peak vertical velocity. Both countermovement and arm-swing significantly (P less than 0.05) improved jump height, but arm-swing's effect was greater, enhancing peak total body center of mass (TBCM) rise both pre and posttakeoff. Countermovement only affected the post-takeoff rise. The arm-swing resulted in higher peak VGRF and peak positive power. During countermovement, the use of arms resulted in less unweighting, slower and less extensive TBCM drop, and less negative power. Countermovement increased pretakeoff jump duration by 71-76%, increased average positive power, and yielded large positive and negative impulses. High test-retest reliability was shown for jump descriptive variables. Body weight together with peak posttakeoff TBCM rise effectively predicted peak power (multiple R2 = 0.89, standard error of estimate = 243 W). The results lend insight into which jumping techniques are most appropriate for given sports situations and indicate that a jump test can effectively be used to estimate peak power output.

Perceived muscle soreness ratings, serum creatine kinase (CK) activity, and myoglobin levels were assessed in three groups of subjects following two 30-min exercise bouts of downhill running (-10 degrees slope). The two bouts were separated by 3, 6, and 9 wk for groups 1, 2, and 3, respectively. Criterion measures were obtained pre- and 6, 18, and 42 h postexercise. On bout 1 the three groups reported maximal soreness at 42 h postexercise. Also, relative increases in CK for groups 1, 2, and 3 were 340, 272, and 286%, respectively. Corresponding values for myoglobin were 432, 749, and 407%. When the same exercise was repeated, significantly less soreness was reported and smaller increases in CK and myoglobin were found for groups 1 and 2. For example, the percent CK increases on bout 2 for groups 1 and 2 were 63 and 62, respectively. Group 3 demonstrated no significant difference in soreness ratings, CK activities, or myoglobin levels between bouts 1 and 2. It was concluded that performance of a single exercise bout had a prophylactic effect on the generation of muscle soreness and serum protein responses that lasts up to 6 wk.

Intra-abdominal pressure (IAP) has been widely hypothesized to reduce potentially injurious compressive forces on spinal discs during lifting. To investigate the effects of a standard lifting belt on IAP and lifting mechanics, IAP and vertical ground reaction force (GRF) were monitored by computer using a catheter transducer and force platform while nine subjects aged 28.2 +/- 6.6 yr dead-lifted a barbell both with and without a lifting belt at 90% of maximum. Both IAP and GRF rose sharply from the time force was first exerted on the bar until shortly after it left the floor, after which GRF usually plateaued while IAP either plateaued or declined. IAP rose significantly (P less than 0.05) earlier with than without the belt. When the belt was worn, IAP rose significantly earlier than did GRF. Both with and without the belt, IAP ended its initial surge significantly earlier than did GRF. Variables significantly greater with than without a belt included peak IAP, area under the IAP vs time curve from start of initial IAP surge to lift-off, peak rate of IAP increase after the end of its initial surge, and average IAP from lift-off to life completion. In contrast, average rate of IAP increase during its initial surge was significantly lower with the belt. Correlations are presented which provide additional information about relationships among the variables. Results suggest that the use of a lifting belt increases IAP, which may reduce disc compressive force and improve lifting safety.

To develop and validate a mathematical model of the relationship between endurance time (T) and power production, 15 male subjects were first tested for maximal power on an instrumented cycle ergometer at 60 rpm. On subsequent days, they were tested for T at various percentages of maximal power. Curves of T as a function of percent maximal power were curvilinear, and could be made to overlap among subjects by individual abscissa scaling, which resulted in the appearance of horizontal stretching or compression of the curves. The degree of stretching-compression was defined by a statistically obtained scaling factor (F) which served to quantify each subject's endurance ability at fractions of maximal power. F was used to transform percent of maximal power to a scaled power variable (Psc). A curve of the form T = a(Psc)b was developed on 10 of the subjects and validated on the remaining five. Correlation between predicted and actual T was 0.967 for the fitting group and 0.980 for the validation group. A maximal power test and a single endurance test at 40 to 50% of maximal power were found to establish individual endurance-power curves fairly well, with a correlation of 0.828 between actual and predicted T. The combination of F and maximal power for a given physical activity provide a useful profile of an individual's ability to perform at constant exercise intensity.

The use of resistance training for children has increased in popularity and interest. It appears that children are capable of voluntary strength gains. Exercise prescription in younger populations is critical and requires certain program variables to be altered from adult perspectives. Individualization is vital, as the rate of physiological maturation has an impact on the adaptations that occur. The major difference in programs for children is the use of lighter loads (i.e., > 6 RM loads). It appears that longer duration programs (i.e., 10-20 wks) are better for observing training adaptations. This may be due to the fact that it takes more exercise to stimulate adaptational mechanisms related to strength performance beyond that of normal growth rates. The risk of injury appears low during participation in a resistance training program, and this risk is minimized with proper supervision and instruction. Furthermore, with the incidence of injury in youth sports, participation in a resistance training program may provide a protective advantage in one's preparation for sports participation.

In order to investigate intra-thoracic pressure (ITP) and intra-abdominal pressure (IAP) during lifting and jumping, 11 males were monitored as they performed the dead lift (DL), slide row (SR), leg press (LP), bench press (BP), and box lift (BL) at 50, 75 and 100% of each subject's four-repetition maxima, the vertical jump (VJ), drop jump (DJ) from 0.5 and 1.0 m heights, and Valsalva maneuver (VM). Measurements were made of peak pressure, time from pressure rise to switch-marked initiation of body movement, and time from the movement to peak pressure. The highest ITP and IAP occurred during VM (22.2 +/- 6.0 and 26.6 +/- 6.7 kPa, respectively) with one individual reaching 36.9 kPa (277 mm Hg) IAP. In ascending order of peak ITP during the highest resistance sets, the activities were SR, BP, VJ, DJ, DL, BL, LP, and VM, while the order for IAP was BP, VJ, DJ, BL, DL, LP, SR, and VM. Pressures significantly (P less than 0.05) increased with amount of weight lifted, rising before and peaking after the weight moved. IAP generally rose earlier and was of greater magnitude than ITP. For the jumps, pressure rose and diminished before the feet lost contact with the ground. Drop-jump height did not affect pressure. Correlation of pressure with weight lifted was fair to good for most activities.