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Kossow, AJ, DeChiara, TG, Neahous, SM, and Ebben, WP. Kinetic analysis of horizontal plyometric exercise intensity. J Strength Cond Res 32(5): 1222-1229, 2018-Plyometric exercises are frequently performed as part of a strength and conditioning program. Most studies assessed the kinetics of plyometric exercises primarily performed in the vertical plane. The purpose of this study was to evaluate the multiplanar kinetic characteristics of a variety of plyometric exercises, which have a significant horizontal component. This study also sought to assess sex differences in the intensity progression of these exercises. Ten men and 10 women served as subjects. The subjects performed a variety of plyometric exercises including the double-leg hop, standing long jump, single-leg standing long jump, bounding, skipping, power skipping, cone hops, and 45.72-cm hurdle hops. Subjects also performed the countermovement jump for comparison. All plyometric exercises were evaluated using a force platform. Dependent variables included the landing rate of force development and landing ground reaction forces for each exercise in the vertical, frontal, and sagittal planes. A 2-way mixed analysis of variance with repeated-measures for plyometric exercise type demonstrated main effects for exercise type for all dependent variables (p ≤ 0.001). There was no significant interaction between plyometric exercise type and sex for any of the variable assessed. Bonferroni-adjusted pairwise comparisons identified a number of differences between the plyometric exercises for the dependent variables assessed (p ≤ 0.05). These findings should be used to guide practitioners in the progression of plyometric exercise intensity, and thus program design, for those who require significant horizontal power in their sport.

This study examined and compared the acute effects of ballistic and nonballistic concentric-only half-squats (COHSs) on squat jump performance. Fifteen resistance-trained men performed a squat jump 2 minutes after a control protocol or 2 COHSs at 90% of their 1 repetition maximum (1RM) COHS performed in a ballistic or nonballistic manner. Jump height (JH), peak power (PP), and allometrically scaled peak power (PPa) were compared using three 3 × 2 repeated-measures analyses of variance. Statistically significant condition × time interaction effects existed for JH (p = 0.037), PP (p = 0.041), and PPa (p = 0.031). Post hoc analysis revealed that the ballistic condition produced statistically greater JH (p = 0.017 and p = 0.036), PP (p = 0.031 and p = 0.026), and PPa (p = 0.024 and p = 0.023) than the control and nonballistic conditions, respectively. Small effect sizes for JH, PP, and PPa existed during the ballistic condition (d = 0.28-0.44), whereas trivial effect sizes existed during the control (d = 0.0-0.18) and nonballistic (d = 0.0-0.17) conditions. Large statistically significant relationships existed between the JH potentiation response and the subject's relative back squat 1RM (r = 0.520; p = 0.047) and relative COHS 1RM (r = 0.569; p = 0.027) during the ballistic condition. In addition, large statistically significant relationship existed between JH potentiation response and the subject's relative back squat strength (r = 0.633; p = 0.011), whereas the moderate relationship with the subject's relative COHS strength trended toward significance (r = 0.483; p = 0.068). Ballistic COHS produced superior potentiation effects compared with COHS performed in a nonballistic manner. Relative strength may contribute to the elicited potentiation response after ballistic and nonballistic COHS.

Ebben, WP, Fauth, ML, Garceau, LR, and Petushek, EJ. Kinetic quantification of plyometric exercise intensity. J Strength Cond Res 25(12): 3288-3298, 2011-Quantification of plyometric exercise intensity is necessary to understand the characteristics of these exercises and the proper progression of this mode of exercise. The purpose of this study was to assess the kinetic characteristics of a variety of plyometric exercises. This study also sought to assess gender differences in these variables. Twenty-six men and 23 women with previous experience in performing plyometric training served as subjects. The subjects performed a variety of plyometric exercises including line hops, 15.24-cm cone hops, squat jumps, tuck jumps, countermovement jumps (CMJs), loaded CMJs equal to 30% of 1 repetition maximum squat, depth jumps normalized to the subject's jump height (JH), and single leg jumps. All plyometric exercises were assessed with a force platform. Outcome variables associated with the takeoff, airborne, and landing phase of each plyometric exercise were evaluated. These variables included the peak vertical ground reaction force (GRF) during takeoff, the time to takeoff, flight time, JH, peak power, landing rate of force development, and peak vertical GRF during landing. A 2-way mixed analysis of variance with repeated measures for plyometric exercise type demonstrated main effects for exercise type and all outcome variables (p ≤ 0.05) and for the interaction between gender and peak vertical GRF during takeoff (p ≤ 0.05). Bonferroni-adjusted pairwise comparisons identified a number of differences between the plyometric exercises for the outcome variables assessed (p ≤ 0.05). These findings can be used to guide the progression of plyometric training by incorporating exercises of increasing intensity over the course of a program.

Concurrent activation potentiation enhances muscular force during open kinetic chain isometric and isokinetic exercises via remote voluntary contractions (RVCs). The purpose of this study was to evaluate the effect of RVCs on the performance of closed kinetic chain ground-based exercises. Subjects included 13 men (21.4+/-1.5 years) who performed the back squat and jump squat in 2 test conditions. The RVC condition included performing the test exercises while clenching the jaw on a mouth guard, forcefully gripping and pulling the barbell down into the trapezius, and performing a Valsalva maneuver. The normal condition (NO-RVC) included performing the test exercises without RVCs. Exercises were assessed with a force platform. Peak ground reaction force (GRF), rate of force development (RFD) during the first 100 milliseconds (RFD-100), RFD to peak GRF (RFD-P), and jump squat height (JH) were calculated from the force-time records. Data were analyzed using an analysis of variance. Results reveal that GRF and RFD-100 were higher in the RVC compared with the NO-RVC condition for both the back squat and jump squat (p

This study evaluated gender differences in the magnitude and timing of hamstring and quadriceps activation during activities that are believed to cause anterior cruciate ligament (ACL) injuries. Twelve men (age = 21.0 +/- 1.2 years; body mass = 81.61 +/- 13.3 kg; and jump height = 57.61 +/- 10.15 cm) and 12 women (age = 19.91 +/- 0.9 years; body mass = 64.36 +/- 6.14 kg; and jump height = 43.28 +/- 7.5) performed 3 repetitions each of the drop jump (jump) normalized to the subject's vertical jump height, and a sprint and cut at a 45-degree angle (cut). Electromyography (EMG) was used to quantify rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), lateral hamstring (LH), and medial hamstrings (MH) activation, timing, activation ratios, and timing ratios before and after foot contact for the jump and cut and normalized to each subject's hamstring and quadriceps maximum voluntary isometric contraction. Data were analyzed using an analysis of variance with results demonstrating that during the postcontact phase of the cut, men demonstrated greater LH and MH activation than women. In the precontact phase of the jump, men showed earlier activation of the VL and VM, than women. Women produced longer RF and VM muscle bursts during the postcontact phase of the cut. Additionally, men showed a trend toward higher hamstring to quadriceps activation ratio than women for the postcontact phase of the cut. This study provides evidence that men are LH dominant during the postcontact phase of the cut compared with women, whereas women sustain RF activation longer than men during this phase. Men activate quadriceps muscles earlier than women in the precontact phase of the jump. Training interventions may offer the potential for increasing the rate and magnitude of hamstring muscle activation. These outcomes should be evaluated using EMG during movements that are similar to those that cause ACL injuries to determine if gender differences in muscle activation can be reduced.

This study describes the results of a survey of high school strength and conditioning coaches (coaches). Thirty-nine of 128 (30.5%) coaches who were surveyed responded, representing 24 of the states of the United States. This survey examines the coaches' personal background information, compensation, job responsibilities, schools, facilities, the advantages and disadvantages of their positions, things they would like to change, and unique aspects of their program. The coaches averaged 6.74 and 14.89 years in their present positions and profession, respectively. All but one coach was certified, with 83% of the survey respondents certified by the National Strength and Conditioning Association. More than half of the coaches (54%) had master's degrees. Coaches worked an average of 9.13 hours a day, beginning and ending their work day on average at 7:34 and 5:07, am and pm, respectively. Coaches' salaries, normalized to a 12-month contract for comparison, averaged approximately 57,866 dollars and 55,214 dollars for those who were and were not part of the teacher's contract, respectively. Coaches who were not salaried were paid an average of $25.90 per hour. Coaches functioned in a variety of roles in their school in addition to their work as a strength and conditioning coach. The coaches' schools averaged approximately 1475 and 429 students and student athletes, respectively. The average strength and conditioning facility size was approximately 3631 ft, resulting in an average of 9.92 ft per athlete. Daily use averaged approximately 192 students. Coaches described the types of equipment and a variety of other facilities used to train athletes. Coaches also reported the advantages, disadvantages, and unique aspects of their work in high school strength and conditioning. Thirty-three of 39 coaches desired to continue as a high school strength and conditioning coach. A variety of other data are described. This study serves as a comprehensive source of information about high school coaches' profiles and positions.

Plyometric exercises are frequently used in strength and conditioning and rehabilitation programs because the landing phase of these exercises requires dynamic stabilization. This study examined the differences in landing stability of a variety of plyometric exercises by assessing time to stabilization (TTS), its reliability, and sex differences therein. Forty-nine men and women performed a variety of plyometric exercises thought to represent a continuum of difficulty of dynamic stabilization during landing. Plyometric exercises included line hops, cone hops, squat jumps, tuck jumps, countermovement jumps, dumbbell countermovement jumps, and single leg countermovement jumps, each performed for 3 repetitions on a force platform. A 2-way mixed analysis of covariance with repeated measures for plyometric exercise type was used to evaluate the main effects for plyometric exercise type and the interaction between plyometric exercise type and sex for TTS. Subject jumping ability was evaluated as a covariate. Results revealed significant main effects for plyometric exercise type (por = 0.001) and for the interaction between plyometric exercise type and sex (p = 0.002). Bonferroni adjusted post hoc analysis demonstrated differences in TTS between a number of plyometric exercises for men and women. Reliability analysis revealed intraclass correlation coefficients ranging from 0.51 to 0.86 with no significant difference between trials (p0.05). Practitioners who use plyometrics to train dynamic stability should create programs that progress the intensity of the exercises based on the results of this study. This study also demonstrated that TTS is moderately to highly reliable for a variety of jumping conditions for both men and women.

Purpose:The purpose of this study was to evaluate differences in hamstring activation during lower body resistance training exercises. This study also sought to assess differences in hamstring-to-quadriceps muscle activation ratios and gender differences therein.Methods:A randomized repeated measures design was used to compare six resistance training exercises that are commonly believed to train the hamstrings, including the squat, seated leg curl, stiff leg dead lift, single leg stiff leg dead lift, good morning, and Russian curl. Subjects included 34 college athletes. Outcome measures included the biceps femoris (H) and rectus femoris (Q) electromyography (EMG) and the H-to-Q EMG ratio, for each exercise.Results:Main effects were found for the H (P < 0.001) and Q (P < 0.001). Post hoc analysis identified the specific differences between exercises. In addition, main effects were found for the H-to-Q ratio when analyzed for all subjects (P < 0.001). Further analysis revealed that women achieved between 53.9 to 89.5% of the H-to-Q activation ratios of men, for the exercises assessed. In a separate analysis of strength matched women and men, women achieved between 35.9 to 76.0% of the H-to-Q ratios of men, for these exercises.Conclusions:Hamstring resistance training exercises offer differing degrees of H and Q activation and ratios. Women compared with men, are less able to activate the hamstrings and/or more able to activate the quadriceps. Women may require disproportionately greater training for the hamstrings compared with the quadriceps.

This study assessed bilateral facilitation and laterality during counter-movement jumps. 23 NCAA Division-I athletes (13 men, 10 women) who participated in track and field volunteered to serve as participants and performed bilateral, right, and left leg countermovement jumps on a force plate. Dependent variables included jump height, reactive strength index, and time to stabilization. A one-way analysis of variance showed significant sex differences in single-leg and bilateral jump height and left leg and bilateral reactive strength index. No sex differences were found for time to stabilization. A repeated-measures analysis of variance indicated significant main effects for jump height and reactive strength index but not for time to stabilization. Bonferroni adjusted pairwise comparisons showed that bilateral jump height and reactive strength index values were different from the unilateral conditions. No differences were found between the right and left legs for jump height, reactive strength index, or time to stabilization. Results indicated no evidence of laterality as assessed by jump height, reactive strength index, and time to stabilization. Bilateral facilitation was found as assessed by jump height and reactive strength index. Time to stabilization demonstrated a bilateral deficit phenomenon.

The study assessed the effect of current activation potentiation by evaluating jaw clenching and its effect on the rate of force development (RFD), time to peak force (TTPF), and peak force (PF) during the countermovement jump. Fourteen subjects performed the countermovement jump on a force platform while maximally clenching their jaw on a dental vinyl mouthguard (JAW) as well as without clenching their jaw by jumping with an open mouth (NON-JAW). Results reveal that the RFD was 19.5% greater in the JAW compared with the NON-JAW condition (p < 0.05). The TTPF was 20.15% less in the JAW compared with the NON-JAW condition (p < 0.05). There were no significant differences (p = 0.60) in PF between the JAW and NON-JAW conditions. These findings indicate that concurrent activation potentiation is manifested through jaw clenching during the countermovement jump. As a result, athletes may employ this strategy of maximally clenching their jaws to gain an ergogenic advantage during the countermovement jump.

The reliability of the reactive strength index (RSI) and time to stabilization (TTS) during maximal-effort plyometric depth jumps was examined. Twenty-two subjects performed three depth jumps from a height of 30 cm. Measures such as height of jump (JH), ground-contact time (CT), RSI, and TTS were obtained and analyzed for reliability using Cronbach alpha reliability coefficient and intraclass correlations. The JH, CT, and RSI were shown to be highly reliable from trial to trial (evidenced by high Cronbach reliability coefficients (alpha > 0.95) and high single- and average-measures intraclass correlations (>0.9). Time to stabilization was not reliable from trial to trial, as evidenced by a low Cronbach reliability coefficient (alpha < 0.7) and poor single- (

The purpose of this study was to investigate the motor unit activation of the quadriceps (Q), hamstring (H), and gastrocnemius (G) muscle groups during a variety of plyometric exercises to further understand the nature of these exercises. Twenty-three athletes volunteered to perform randomly ordered plyometric exercises, thought to cover a continuum of intensity levels, including two-foot ankle hops; 15-cm cone hops; tuck, pike, and box jumps; one- and two-leg vertical jump and reach; squat jumps with approximately 30% of their 1RM squat load; and 30- and 61-cm depth jumps. Integrated electromyographic data were analyzed for each exercise using a one-way repeated-measures ANOVA. Results revealed significant main effects for the Q when all subjects are analyzed, as well as for separate analysis of men, women, subjects with vertical jumps greater than 50 cm, and those with vertical jumps less than or equal to 50 cm (p < or = 0.05). Significant main effects were also found for the G muscle group in the analysis of all subjects, as well as for men and subjects with vertical jumps greater than 50 cm (p < or = 0.05). No significant main effects were found for the H muscle group. Pairwise comparisons revealed a variety of differences among plyometric exercises. In some cases, plyometrics previously reported to be of high intensity, such as the depth jump, yielded relatively little motor unit recruitment compared with exercises typically thought to be of low intensity. Results can assist the practitioner in creating plyometric programs based on the nature of the motor unit recruitment.

Suchomel, TJ, Sato, K, DeWeese, BH, Ebben, WP, and Stone, MH. Potentiation following ballistic and nonballistic complexes: the effect of strength level. J Strength Cond Res 30(7): 1825-1833, 2016-The purpose of this study was to compare the temporal profile of strong and weak subjects during ballistic and nonballistic potentiation complexes. Eight strong (relative back squat = 2.1 ± 0.1 times body mass) and 8 weak (relative back squat = 1.6 ± 0.2 times body mass) males performed squat jumps immediately and every minute up to 10 minutes following potentiation complexes that included ballistic or nonballistic concentric-only half-squat (COHS) performed at 90% of their 1 repetition maximum COHS. Jump height (JH) and allometrically scaled peak power (PPa) were compared using a series of 2 × 12 repeated measures analyses of variance. No statistically significant strength level main effects for JH (p = 0.442) or PPa (p = 0.078) existed during the ballistic condition. In contrast, statistically significant main effects for time existed for both JH (p = 0.014) and PPa (p0.001); however, no statistically significant pairwise comparisons were present (p0.05). Statistically significant strength level main effects existed for PPa (p = 0.039) but not for JH (p = 0.137) during the nonballistic condition. Post hoc analysis revealed that the strong subjects produced statistically greater PPa than the weaker subjects (p = 0.039). Statistically significant time main effects existed for time existed for PPa (p = 0.015), but not for JH (p = 0.178). No statistically significant strength level × time interaction effects for JH (p = 0.319) or PPa (p = 0.203) were present for the ballistic or nonballistic conditions. Practical significance indicated by effect sizes and the relationships between maximum potentiation and relative strength suggest that stronger subjects potentiate earlier and to a greater extent than weaker subjects during ballistic and nonballistic potentiation complexes.

The purposes of this study were to examine the effect of ballistic concentric-only half-squats (COHS) on subsequent squat-jump (SJ) performances at various rest intervals and to examine the relationships between changes in SJ performance and bilateral symmetry at peak performance. Thirteen resistance-trained men performed an SJ immediately and every minute up to 10 min on dual force plates after 2 ballistic COHS repetitions at 90% of their 1-repetition-maximum COHS. SJ peak force, peak power, net impulse, and rate of force development (RFD) were compared using a series of 1-way repeated-measures ANOVAs. The percent change in performance at which peak performance occurred for each variable was correlated with the symmetry index scores at the corresponding time point using Pearson correlation coefficients. Statistical differences in peak power (P = .031) existed between rest intervals; however, no statistically significant pairwise comparisons were present (P > .05). No statistical differences in peak force (P = .201), net impulse (P = .064), and RFD (P = .477) were present between rest intervals. The relationships between changes in SJ performance and bilateral symmetry after the rest interval that produced the greatest performance for peak force (r = .300, P = .319), peak power (r = –.041, P = .894), net impulse (r = –.028, P = .927), and RFD (r = –.434, P = .138) were not statistically significant. Ballistic COHS may enhance SJ performance; however, the changes in performance were not related to bilateral symmetry.

The purpose of this study was to compare mean integrated electromyographic values (EMG(int)) during biomechanically comparable closed kinetic chain/fixed external load, open kinetic chain/moveable no load, and moveable external load exercises.EMG(int) were obtained for the pectoralis major (PM) and the long head of the triceps (T) during absorption and force phases of three biomechanically comparable exercises: the push-up (PU); the bench press-load (BP-L); and the bench press-no load (BP-NL) equated to the closed kinetic chain/fixed external load; moveable external load; and open kinetic chain/moveable no load conditions respectively. A force plate was used to equate load for the PU and BP-L exercises. Ten males (24+/-4.4 yr) participated in the three randomly ordered exercises. A pronated, closed grip was used for all exercises. The mean integrated EMG values from three isometric maximal voluntary contractions were used to determine a reference EMG (EMG(MVC)) for each muscle. Normalized EMG values (NEMG) were determined by EMG(int)/EMG(Mvc) and analyzed by one-factor repeated measures ANOVA for each muscle (PM and T) during each phase (absorption and force).There was no significant difference (P0.05) between the equivalently loaded, different boundary exercises (PU and BP). Statistical significance (P0.05) was determined between the differently loaded, equivalent boundary exercises (BP and BP-NL) as well as the differently loaded, different boundary exercises (PU and BP-NL).Results from this study support the theory that activities of similar biomechanical motions and mass of loading, regardless of the boundary condition, have comparable EMG values of primary muscle groups. In addition, this study suggests external load is more important than boundary condition in describing human activity.

Instruction and assessment strategies of undergraduate introductory biomechanics instructors have yet to be comprehensively examined. The purpose of this study was to identify the current instruction and assessment practices of North American undergraduate introductory biomechanics instructors and equipment needed for effective instruction in lecture and laboratory sessions. One hundred and sixty-five respondents (age: 42.5 +/- 10.3 years) who currently teach or have taught an introductory biomechanics course in North America were recruited by electronic mail. Subjects completed a web-based survey, consisting of 60 open- and closed-ended questions. Pearson's correlation coefficients were used to assess relationships between instructor's familiarity with either the Biomechanics Concept Inventory or the NASPE Guidelines for Undergraduate Biomechanics, and instructor and course characteristics (number of years teaching, age, faculty rank, number of quizzes given, etc.) A number of variables were significantly (p0.05) correlated. Answers to open-ended questions were processed using content analysis, with results categorized in content areas including: instructor and course characteristics; lecture instruction; assessment and equipment; laboratory instruction; assessment and equipment; and instructor's perspectives. Many active learning strategies for lecture and laboratory instruction were identified by faculty. Limited student preparation and limited resources were noted as the instructor's most common challenges.

The osteogenic potential of exercise is reported to be partially a function of the magnitude of training loads. This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the eccentric and concentric phases of the back squat at 3 different loads. Twelve subjects performed the back squat on a force platform with loading conditions of 80, 100, and 120% of their 1 repetition maximum (RM). Back squats performed at 120% of the 1RM produced the highest GRF in both the eccentric and concentric conditions. No significant differences were found between RFD for any of the loading conditions. Performing the back squat at loads of 120% of the estimated 1RM, accomplished with reduced range of motion, results in higher GRF than the back squat performed at 80 or 100% of the 1RM. Thus, supermaximal back squat loads in excess of the 1RM, with decreased range of motion, may be a useful part of a resistance training program designed to maximize osteogenic potential.

Push-ups are a common and practical exercise that is used to enhance fitness, including upper body strength or endurance. The kinetic characteristics of push-ups and its variations are yet to be quantified. Kinetic quantification is necessary to accurately evaluate the training load, and thus the nature of the training stimulus, for these exercise variations. This study assessed the peak vertical ground reaction forces (GRFs) of push-up variations including the regular push-up and those performed with flexed knee, feet elevated on a 30.48-cm box, and a 60.96-cm box, and hands elevated on a 30.48-cm box and a 60.96-cm box. Twenty-three recreationally fit individuals (14 men, 9 women) performed each of the 6 push-up variations in a randomized order. Peak GRF and peak GRF expressed as a coefficient of subject body mass were obtained with a force platform. Push-ups with the feet elevated produced a higher GRF than all other push-up variations (p ≤ 0.05). Push-ups with hands elevated and push-ups from the flexed knee position produced a lower GRF than all other push-up variations (p ≤ 0.05). No gender differences in response to these push-up variations were found (p > 0.05). Additionally, subject height was not related to the GRF for any of the push-up conditions (p > 0.05) other than the condition where hands were elevated on a 60.96-cm box (p ≤ 0.05; r = 0.63). These data can be used to progress the intensity of push-ups in a program and to quantify the training load as a percentage of body mass.

The ability to develop force quickly is a requisite ability in most sports. The reactive strength index (RSI) has been developed as a measure of explosive strength and is derived by evaluating jump height divided by ground contact time during the depth jump (DJ). At present, the RSI is typically used to evaluate DJ performance, because it is the only plyometric exercise with an identifiable ground contact time. The purpose of this study was to introduce a modification of the RSI (RSImod) that can be used to evaluate the explosive power of any vertical plyometric exercise. This study will also assess the reliability of the RSImod, evaluate the RSImod of a variety of plyometric exercises, and examine gender differences. Twenty-six men and 23 women served as subjects. Subjects performed 3 repetitions for each of 5 plyometric exercises including the countermovement jump (CMJ), tuck jump, single-leg jump, squat jump, and dumbbell CMJ. Data were analyzed using a 2-way analysis of variance to evaluate differences in RSImod between the plyometric exercise and the interaction between plyometric exercise RSImod and gender. The analysis of RSImod revealed significant main effects for plyometric exercise type (por= 0.001) but not for the interaction between plyometric exercise type and gender (p0.05). Results of pairwise comparisons indicate that the RSImod is statistically different between all plyometric exercises studied. Intraclass correlation coefficients indicate that RSImod is highly reliable for all of the exercises studied. The RSImod offers a highly reliable method of assessing the explosiveness developed during a variety of plyometric exercises.

The reliability of electromyographic (EMG) data has been examined for isometric and slow dynamic tasks, but little is known about the repeatability of this data for ballistic movements. The purpose of this study was to examine the within-session, trial-to-trial reliability of a variety of quadriceps and hamstrings muscles during isometric and ballistic activities. Data were analyzed by way of intraclass correlation coefficients (ICC), intersubject coefficients of variation (CVinter), and intrasubject coefficients of variation (CVintra). Twenty-four subjects performed 3 repetitions each of 2 randomly ordered test exercises, including landing from a depth jump (J) and cutting after a 10-m sprint (C). Data were acquired and processed with root mean square EMG for the muscles assessed, and data were analyzed for each exercise using a repeated measures analysis of variance. Results revealed that all ICC values were greater than 0.80, with most values greater than 0.90, CVinter values ranged from 5.4% to 148.7%, and CVintra values ranged from 11.5% to 49.3%. This study indicates that EMG is a reliable method for assessing the reproducibility of both the quadriceps and hamstrings muscle activation during either isometric or ballistic exercises.

The purpose of this study was to determine whether there is a linear relationship between the squat and a variety of hamstring resistance training exercises, and whether this relationship differs on the basis of sex. This study also sought to create prediction equations for the determination of hamstring exercise load based on the squat load. Repetition maximums of the squat, as well as 4 common hamstring resistance training exercises including the seated leg curl, stiff leg dead lift, single leg dead lift, and good morning exercise, were determined for each subject. Subjects included 21 men and 13 women collegiate athletes. Data were evaluated using linear regression analysis to predict hamstring exercise loads from 6 repetition maximum squat data. Results of the analysis of all subjects indicated that squat load was a significant predictor of loads for each of the hamstring exercises. However, separate analysis of women revealed that squat load was not a significant predictor of loads for any of the hamstring exercises. Analysis of the men revealed that squat was a significant predictor of load for the seated leg curl (R = 0.58, p < 0.001), stiff leg dead lift (R = 0.82, p < 0.001), single leg stiff leg dead lift (R = 0.80, p < 0.001), and good morning (R = 0.79, p < 0.001) exercises. On the basis of the analysis of the men, the following prediction equations were devised for each exercise: (1) seated leg curl load = squat load (0.186) + 10.935 kg, (2) stiff leg deadlift load = squat load (1.133) - 86.331 kg, (3) single leg stiff leg deadlift load = squat load (0.443) - 3.425 kg, and (4) good morning load = squat load (0.961) - 105.505 kg. Thus, results from testing core exercises such as the squat can provide useful data for the assignment of loads for assistance exercises.

This study evaluated the effect of remote voluntary contractions(RVC) on concentric isokinetic knee extensor and flexor peak torque, rate of torque development, power, and work, the activation of the affected muscles, and gender differences therein.Eleven men and 12 women were evaluated with EMG and isokinetic dynamometry during knee extension and flexion tests in RVC and baseline (NO-RVC) test conditions. The RVC condition included jaw clenching, hand gripping, and the Valsalva maneuver. A two-way mixed ANOVA with repeated measures for test condition was used to evaluate the main effects for each isokinetic measure, as well as the EMG of the prime movers, their antagonist,and the muscles involved in the RVC, and the interaction between test condition and gender.Significant interactions between test condition and gender indicate differences in response to RVC during knee extension tests for power and work (Por = 0.05) and for knee flexion tests for peak torque and power (Por = 0.05). All subjects produced higher peak torque and power during knee extension in the RVC condition (Por = 0.05). Men produced a higher rate of torque development and work during knee extension (Por = 0.05) and a higher peak torque and power during knee flexion in the RVC condition (Por = 0.05). Prime mover activation was greater in the RVC condition for most tests (Por = 0.05). Women demonstrated lower bilateral flexor digitorum superficialis activation than men during all tests in the RVC condition (Por = 0.05).RVC increased the performance of several outcome variables assessed, which coincides with the concomitant increase in EMG of the prime movers.

This study describes the results of a survey of the practices of high school strength and conditioning (HS S&C) coaches. Thirty-eight of 128 (29.7%) HS S&C coaches, who were surveyed, responded. This survey examines background information, physical testing, flexibility development, speed development, agility development, plyometrics, strength/power development and program design, nutrition, and injury frequency. High school strength and conditioning coaches average 14.78 years in the profession, and 89% of the survey respondents were certified by the National Strength and Conditioning Association. Coaches assess an average of 5.83 different parameters of fitness, with strength as well as power being the most common parameters assessed. Coaches tested an average of 3.86 times a year with an average of 8.51 specific tests per testing session. All HS S&C coaches used a variety of flexibility development strategies using dynamic stretching more frequently than static. Thirty-six of 38 (95%) coaches follow a periodization model, 37 of 38 (97.4%) coaches indicated that their athletes used Olympic-style lifts, and 37 of 37 (100%) coaches responding to this question used plyometric training with their athletes. The squat and its variations, as well as the Olympic-style lifts and its variations, were most frequently identified as the most important exercises prescribed. All coaches use speed development and agility training strategies with their athletes. This survey examined a variety of other practices and provides detailed information about these practices at the high school level. Coaches are encouraged to review the strength and conditioning practices described in this survey and identify and implement the ideas that may improve their practices.

Purpose:This study evaluated a variety of downhill slopes in an effort to determine the optimal slope for overspeed running.Methods:Thirteen NCAA Division III college athletes who participated in soccer, track, and football ran 40-yd (36.6-m) sprints, on downhill slopes of 2.1°, 3.3°, 4.7°, 5.8°, and 6.9° in random order. All sprints were timed using the Brower Timing System Speedtrap II. Data were analyzed with SSPS 15.0. A 1-way repeated-measures analysis of variance revealed significant main effects for the test slopes (P = .000). Bonferroni-adjusted pairwise comparisons determined that there were a number of differences between the hill slopes.Results:Analysis reveals that 40-yd sprints performed on hill slopes of approximately 5.8° were optimal compared with flatland running and the other slopes assessed (P < .05). Sprinting on a 5.8° slope increased the subjects’ maximal speed by an average of 0.35 s, resulting in a 6.5% ± 4.0% decrease in 40-yd sprint time compared with fatland running. Compared with the 4.7° slope, the 5.8° slope yielded a 0.10-s faster 40-yd sprint time, resulting in a 1.9% increase in speed.Conclusions:Those who train athletes for speed should use or develop overspeed hills with slopes of approximately 5.8° to maximize acute sprinting speed. The results of this study bring into question previous recommendations to use hills of 3° downhill slope for this form of overspeed training.

Purpose: Concurrent activation potentiation (CAP) is purported to enhance the force capabilities of muscles via the contraction of muscles remote to the prime mover. This phenomenon has been described as remote voluntary contractions (RVC). The objective of this study was to assess a variety of RVC and their effect on isometric knee extensor torque to evaluate the existence of CAP. Methods: Twelve males who regularly participated in lower body resistance training served as subjects. Subjects performed maximum voluntary isometric contractions (MVIC) of the knee extensors without RVC, as well as in a variety of conditions that included RVC, in a randomized order. The RVC conditions included jaw clenching, bilateral gripping, jaw clenching combined with contralateral gripping and the Valsalva maneuver, and the combination of jaw clenching, bilateral gripping, and the Valsalva maneuver. Results: A repeated-measures ANOVA revealed significant main effects (P = 0.001) for RVC condition. Bonferroni-adjusted post hoc analysis identified several differences in RVC compared with the NO-RVC condition (P < 0.05). The RVC condition including jaw clenching, bilateral gripping, and the Valsalva maneuver resulted in approximately 14.6% and 14.8% greater average and peak torque, respectively, compared with the NO-RVC condition. Conclusions: These findings indicate that RVC augment torque, which may be useful during the performance of resistance training as well as athletic tasks that require acute maximal strength. These findings support the existence of the CAP phenomenon

Because the intensity of plyometric exercises usually is based simply upon anecdotal recommendations rather than empirical evidence, this study sought to quantify a variety of these exercises based on forces placed upon the knee. Six National Collegiate Athletic Association Division I athletes who routinely trained with plyometric exercises performed depth jumps from 46 and 61 cm, a pike jump, tuck jump, single-leg jump, countermovement jump, squat jump, and a squat jump holding dumbbells equal to 30% of 1 repetition maximum (RM). Ground reaction forces obtained via an AMTI force plate and video analysis of markers placed on the left hip, knee, lateral malleolus, and fifth metatarsal were used to estimate rate of eccentric force development (E-RFD), peak ground reaction forces (GRF), ground reaction forces relative to body weight (GRF/BW), knee joint reaction forces (K-JRF), and knee joint reaction forces relative to body weight (K-JRF/BW) for each plyometric exercise. One-way repeated measures analysis of variance indicated that E-RFD, K-JRF, and K-JRF/BW were different across the conditions (p0.05), but peak GRF and GRF/BW were not (p0.05). Results indicate that there are quantitative differences between plyometric exercises in the rate of force development during landing and the forces placed on the knee, though peak GRF forces associated with landing may not differ.

This study describes the results of a survey of the practices of Major League Baseball strength and conditioning (MLB S&C) coaches. The response rate was 70.0% (21 of 30). This survey examines (a) background information, (b) physical testing, (c) flexibility development, (d) speed development, (e) plyometrics, (f) strength/power development, (g) unique aspects, and (h) comments. Results indicate, in part, that coaches assess an average of 3.6 parameters of fitness, with body composition testing being the most commonly assessed parameter. All coaches use a variety of flexibility development strategies. All coaches use speed development strategies, with form running drills being the most common. Twenty of 21 (95.2%) coaches employ plyometric exercises with their athletes. Eighteen of 21 (85.7%) of MLB S&C coaches follow a periodization model (PM). Five of 21 coaches (23.8%) indicated that their athletes use Olympic-style lifts. The squat and its variations and the lunge and its variations were most frequently identified as the first and second most important exercises used to train the athletes. This survey provides detailed information about strength and conditioning practices at the most competitive level of baseball and serves as a review, as well as a source of applied information and new ideas.

This study assessed the effects of hamstring prefatigue on peak torque, peak power, time to peak torque, knee angle of peak torque, and electromyography (EMG) activity of the hamstrings and quadriceps group during knee extensions at angular velocities of 60 degrees, 180 degrees, and 300 degrees.s(-1). Twenty Division I wrestlers performed 5 maximal knee extensions in prefatigued and nonfatigued conditions of the hamstring group. This study demonstrated that when the hamstrings were prefatigued, the quadriceps produced significant decreases in peak torque of 1.7% (p0.05), peak power of 11% (p0.05), and rate to peak torque of 6.4% (p0.01) as compared with the nonfatigued state. When the hamstrings were prefatigued, they produced a 25% greater amount of EMG activity during knee extension (p0.01) than when not prefatigued. There was no significant difference in quadriceps EMG activity whether the hamstring group was prefatigued or not (p0.05). The decrease in quadriceps peak torque during the prefatigued condition was more pronounced (p0.01) at an angular velocity of 60 degrees.s(-1) than at 180 degrees or 300 degrees.s(-1). In other words, prefatiguing the antagonist appears to be most detrimental to torque output of the quadriceps in the condition that most closely replicates the speed at which "isotonic" weight training occurs (60 degrees.s(-1)) and suggests a limitation to agonist-antagonist superset training.

Complex training has been recommended as a method of incorporating plyometrics with strength training. Some research suggests that plyometric performance is enhanced when performed 3-4 minutes after the strength training set, whereas other studies have failed to find any complex training advantage when plyometrics are performed immediately after the strength training portion of the complex. The purpose of this study was to determine if there is an ergogenic advantage associated with complex training and if there is an optimal time for performing plyometrics after the strength training set. Subjects were 21 NCAA Division I athletes who performed a countermovement vertical jump, a set of 5 repetitions maximum (5 RM) squats, and 5 trials of countermovement vertical jump at intervals of 10 seconds and 1, 2, 3, and 4 minutes after the squat. Jump height and peak ground reaction forces were acquired via a force platform. The pre-squat jump performance was compared with the post-squat jumps. Repeated measures ANOVA determined a difference (p/= 0.05) between genders and that jump performance immediately following the squat exercise was hindered (0.66 m), but no effect (p0.05) was found comparing subsequent jumps (0.72-0.76 m) to the pre-squat condition (0.74 m). When comparing high to low strength individuals, there was no effect on jump performance following the squat (p0.05). In conclusion, complex training does not appear to enhance jumping performance significantly and actually decreases it when the jump is performed immediately following the strength training set; however, a nonsignificant trend toward improvement seemed to be present. Therefore to optimize jump performance it appears that athletes should not perform jumps immediately following resistance training. It may be possible that beyond 4 minutes of recovery performance could be enhanced; however, that was not within the scope of the current study.

This study examined mean integrated electromyography (I-EMG) for the quadriceps and hamstring muscle groups, as well as mean and peak vertical ground reaction forces (GRFs), for 3 conditions of the back squat. Conditions included (a) squat with barbell and weight plates, (b) squat with barbell and weight plates plus chains hung on each end of the barbell to replace approximately 10% of the squat load, and (c) squat with barbell and weight plates plus elastic bands offering resistance equivalent to approximately 10% of the squat load. Weight plates equal to the load added by either the chains or elastic bands were removed for the latter 2 squat conditions. Vertical GRFs were obtained during a single testing session for all 3 squat conditions. The tests were performed on a 2-cm thick aluminum platform (0.76 x 1.0 m) bolted directly to a force plate (OR6-5-2000, AMTI, Watertown, MA). Surface electrode I-EMG data from the quadriceps and hamstrings were recorded at 500 Hz. The exercise order was randomly determined for 11 NCAA Division I athletes who had experience using these types of squats. A repeated measures analysis of covariance revealed no differences in I-EMG and GRF during the eccentric or concentric phase for any of the 3 squat conditions. Analyses showed that mean GRF and I-EMG was significantly different between eccentric and concentric phases for all groups. The results question the usefulness of performing squats combining barbell and weight plates with chain and elastic resistance.