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The purpose of this study was firstly to examine the sensitivity of heart rate (HR)-based and subjective monitoring markers to intensified endurance training; and secondly, to investigate the validity of these markers to distinguish individuals in different fatigue states. A total of 24 recreational runners performed a 3-week baseline period, a 2-week overload period, and a 1-week recovery period. Performance was assessed before and after each period with a 3000m running test. Recovery was monitored with daily orthostatic tests, nocturnal HR recordings, questionnaires, and exercise data. The participants were divided into subgroups (overreached/OR, n = 8; responders/RESP, n = 12) based on the changes in performance and subjective recovery. The responses to the second week of the overload period were compared between the subgroups. RESP improved their baseline 3000 m time (p < 0.001) after the overload period (-2.5 ± 1.0%), and the change differed (p < 0.001) from OR (0.6 ± 1.2%). The changes in nocturnal HR (OR 3.2 ± 3.1%; RESP -2.8 ± 3.7%, p = 0.002) and HR variability (OR -0.7 ± 1.8%; RESP 2.1 ± 1.6%, p = 0.011) differed between the subgroups. In addition, the decrease in subjective readiness to train (p = 0.009) and increase in soreness of the legs (p = 0.04) were greater in OR compared to RESP. Nocturnal HR, readiness to train, and exercise-derived HR-running power index had ≥85% positive and negative predictive values in the discrimination between OR and RESP individuals. In conclusion, exercise tolerance can vary substantially in recreational runners. The results supported the usefulness of nocturnal HR and subjective recovery assessments in recognizing fatigue states., (© 2024 The Authors. European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.)

Abstract: Helén, J, Kyröläinen, H, Ojanen, T, Pihlainen, K, Santtila, M, Heikkinen, R, and Vaara, JP. High-intensity functional training induces superior training adaptations compared with traditional military physical training. J Strength Cond Res 37(12): 2477-2483, 2023-This study examined the effectiveness of concurrent strength and endurance training with an emphasis on high-intensity functional training (HIFT) during military service. Voluntary male conscripts (aged 18-28 years) were placed in either an experimental (EXP: n = 50-66) or a control (CON: n = 50-67) group. The training for the EXP group included HIFT using body mass, sandbags, and kettlebells. The CON group trained according to the current practice. Physical performance and body composition were assessed at baseline (PRE), at week 10 (MID), and after (POST) the 19-week training period. Significance was set at p < 0.05. The total distance covered in a 12-minute running test increased in both groups, but the change in EXP was superior to the change in CON (11.6%, ES: 0.79 vs. 5.7%, ES: 0.33; p = 0.027). Maximal strength and power characteristics increased in EXP (3.1-5.0%), whereas no improvements were observed in CON. Conscripts with the highest initial fitness showed no improvements in physical performance in either group. Body mass and waist circumference decreased in EXP, whereas CON showed an increase in muscle mass. These findings suggest that HIFT is an effective and time-efficient approach to improve soldiers' aerobic fitness during military service. For the optimal development of strength, the training equipment used may not have provided sufficient and progressive loading to yield considerable strength adaptations. More focus should be placed on sufficient intensity and volume in both strength and endurance training, especially for the most fit soldiers., (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the National Strength and Conditioning Association.)

Purpose: Long-term development of endurance performance requires a proper balance between strain and recovery. Because responses and adaptations to training are highly individual, this study examined whether individually adjusted endurance training based on recovery and training status would lead to greater adaptations compared with a predefined program., Methods: Recreational runners were divided into predefined (PD; n = 14) or individualized (IND; n = 16) training groups. In IND, the training load was decreased, maintained, or increased twice a week based on nocturnal heart rate variability, perceived recovery, and heart rate-running speed index. Both groups performed 3-wk preparatory, 6-wk volume, and 6-wk interval periods. Incremental treadmill tests and 10-km running tests were performed before the preparatory period ( T0 ) and after the preparatory ( T1 ), volume ( T2 ), and interval ( T3 ) periods. The magnitude of training adaptations was defined based on the coefficient of variation between T0 and T1 tests (high >2×, low <0.5×)., Results: Both groups improved ( P < 0.01) their maximal treadmill speed and 10-km time from T1 to T3 . The change in the 10-km time was greater in IND compared with PD (-6.2% ± 2.8% vs -2.9% ± 2.4%, P = 0.002). In addition, IND had more high responders (50% vs 29%) and fewer low responders (0% vs 21%) compared with PD in the change of maximal treadmill speed and 10-km performance (81% vs 23% and 13% vs 23%), respectively., Conclusions: PD and IND induced positive training adaptations, but the individualized training seemed more beneficial in endurance performance. Moreover, IND increased the likelihood of high response and decreased the occurrence of low response to endurance training., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

Purpose: To assess the reliability of nocturnal heart rate (HR) and HR variability (HRV) and to analyze the sensitivity of these markers to maximal endurance exercise., Methods: Recreational runners recorded nocturnal HR and HRV on nights after 2 identical low-intensity training sessions (n = 15) and on nights before and after a 3000-m running test (n = 23). Average HR, the natural logarithm of the root mean square of successive differences (LnRMSSD), and the natural logarithm of the high-frequency power (LnHF) were analyzed from a full night (FULL), a 4-hour (4H) segment starting 30 minutes after going to sleep, and morning value (MOR) based on the endpoint of the linear fit through all 5-minute averages during the night. Differences between the nights were analyzed with a general linear model, and intraclass correlation coefficient (ICC) was used for internight reliability assessments., Results: All indices were similar between the nights followed by low-intensity training sessions. A very high ICC (P < .001) was observed in all analysis segments with a range of .97 to .98 for HR, .92 to .97 for LnRMSSD, and .91 to .96 for LnHF. HR increased (P < .001), whereas LnRMSSD (P < .01) and LnHF (P < .05) decreased after the 3000-m test compared with previous night only in 4H and FULL. Increments in HR (P < .01) and decrements in LnRMSSD (P < .05) were greater in 4H compared with FULL and MOR., Conclusions: Nocturnal HR and HRV indices are highly reliable. Demanding maximal exercise increases HR and decreases HRV most systematically in 4H and FULL segments.

Purpose: This study examined the physiological, perceptual, and performance responses to a 2-wk block of increased training load and compared whether responses differ between high-intensity interval (HIIT) and low-intensity training (LIT)., Methods: Thirty recreationally trained males and females performed a 2-wk block of 10 HIIT sessions (INT, n = 15) or 70% increased volume of LIT (VOL, n = 15). Running time in the 3000 m and basal serum and urine hormone concentrations were measured before (T1) and after the block (T2), and after a recovery week (T3). In addition, weekly averages of nocturnal heart rate variability (HRV) and perceived recovery were compared with the baseline., Results: Both groups improved their running time in the 3000 m from T1 to T2 (INT = -1.8% ± 1.6%, P = 0.003; VOL = -1.4% ± 1.7%, P = 0.017) and from T1 to T3 (INT = -2.5% ± 1.6%, P < 0.001; VOL = -2.2% ± 1.9%, P = 0.001). Resting norepinephrine concentration increased in INT from T1 to T2 (P = 0.01) and remained elevated at T3 (P = 0.018). The change in HRV from the baseline was different between the groups during the first week (INT = -1.0% ± 2.0% vs VOL = 1.8% ± 3.2%, P = 0.008). Muscle soreness increased only in INT (P < 0.001), and the change was different compared with VOL across the block and recovery weeks (P < 0.05)., Conclusions: HIIT and LIT blocks increased endurance performance in a short period. Although both protocols seemed to be tolerable for recreational athletes, a HIIT block may induce some negative responses such as increased muscle soreness and decreased parasympathetic activity., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

The aims of the current study were to examine the relationships between heart rate variability (HRV), salivary cortisol, sleep duration and training in young athletes. Eight athletes (16 ± 1 years) were monitored for 7 weeks during training and competition seasons. Subjects were training for endurance-based winter sports (cross-country skiing and biathlon). Training was divided into two zones (K1, easy training and K2, hard training). Heart rate and blood lactate during submaximal running tests (SRT), as well as cortisol, sleep duration and nocturnal HRV (RMSSD), were determined every other week. HRV and cortisol levels were correlated throughout the 7-week period (r = -0.552, P = 0.01), with the strongest correlation during week 7 (r = -0.879, P = 0.01). The relative changes in K1 and HRV showed a positive correlation from weeks 1-3 (r = 0.863, P = 0.006) and a negative correlation during weeks 3-5 (r = -0.760, P = 0.029). The relative change in sleep during weeks 1-3 were negatively correlated with cortisol (r = -0.762, P = 0.028) and K2 (r = -0.762, P = 0.028). In conclusion, HRV appears to reflect the recovery of young athletes during high loads of physical and/or physiological stress. Cortisol levels also reflected this recovery, but significant change required a longer period than HRV, suggesting that cortisol may be less sensitive to stress than HRV. Moreover, our results indicated that during the competition season, recovery for young endurance athletes increased in duration and additional sleep may be beneficial., (© Journal of Sports Science and Medicine.)

Purpose: To determine body composition, energy availability, training load, and menstrual status in young elite endurance running athletes (ATH) over 1 year, and in a secondary analysis, to investigate how these factors differ between nonrunning controls (CON), and amenorrheic (AME) and eumenorrheic (EUM) ATH. Correlations to injury, illness, and performance were also examined., Methods: Altogether 13 ATH and 8 CON completed the Low Energy Availability in Females Questionnaire. Anthropometric, energy intake, and peak oxygen uptake assessments were made at 4 time points throughout the year: at baseline post competition season, post general preparation, post specific preparation, and post competition season the following year. Logs of physical activity, menstrual cycle, illness, and injury were kept by all participants. Performance was defined using the highest International Association of Athletics Federations points prior to and after the study., Results: ATH had significantly lower body mass (P < .008), fat percentage (P < .001), and body mass index (P < .027) compared with CON, while energy availability did not differ between ATH and CON. The Low Energy Availability in Females Questionnaire score was higher in ATH than in CON (P < .028), and 8 ATH (vs zero CON) were AME. The AME had significantly more injury days (P < .041) and ran less (P < .046) than EUM, while total annual running distance was positively related to changes in performance in ATH (r < .62, P < .043, n < 11)., Conclusions: More than half of this group of runners was AME, and they were injured more and ran less than their EUM counterparts. Furthermore, only the EUM runners increased their performance over the course of the year.

This study investigated acute responses and post 24-h recovery to four running sessions performed at different intensity zones by supine heart rate variability, countermovement jump, and a submaximal running test. A total of 24 recreationally endurance-trained male subjects performed 90 min low-intensity (LIT), 30 min moderate-intensity (MOD), 6×3 min high-intensity interval (HIIT) and 10×30 s supramaximal-intensity interval (SMIT) exercises on a treadmill. Heart rate variability decreased acutely after all sessions, and the decrease was greater after MOD compared to LIT and SMIT (p<0.001; p<0.01) and HIIT compared to LIT (p<0.01). Countermovement jump decreased only after LIT (p<0.01) and SMIT (p<0.001), and the relative changes were different compared to MOD (p<0.01) and HIIT (p<0.001). Countermovement jump remained decreased at 24 h after SMIT (p<0.05). Heart rate during the submaximal running test rebounded below the baseline 24 h after all sessions (p<0.05), while the rating of perceived exertion during the running test remained elevated after HIIT (p<0.05) and SMIT (p<0.01). The current results highlight differences in the physiological demands of the running sessions, and distinct recovery patterns of the measured aspects of performance. Based on these results, assessments of performance and recovery from multiple perspectives may provide valuable information for endurance athletes, and help to improve the quality of training monitoring., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

The purpose of the study was to examine the effects of progressively increased training intensity or volume on the nocturnal heart rate (HR) and heart rate variability (HRV), countermovement jump, perceived recovery, and heart rate-running speed index (HR-RS index). Another aim was to analyze how observed patterns during the training period in these monitoring variables were associated with the changes in endurance performance. Thirty recreationally trained participants performed a 10-week control period of regular training and a 10-week training period of either increased training intensity (INT, n = 13) or volume (VOL, n = 17). Changes in endurance performance were assessed by an incremental treadmill test. Both groups improved their maximal speed on the treadmill (INT 3.4 ± 3.2%, p < 0.001; VOL 2.1 ± 1.8%, p = 0.006). In the monitoring variables, only between-group difference ( p = 0.013) was found in nocturnal HR, which decreased in INT ( p = 0.016). In addition, perceived recovery decreased in VOL ( p = 0.021) and tended to decrease in INT ( p = 0.056). When all participants were divided into low-responders and responders in maximal running performance, the increase in the HR-RS index at the end of the training period was greater in responders ( p = 0.005). In conclusion, current training periods of increased intensity or volume improved endurance performance to a similar extent. Countermovement jump and HRV remained unaffected, despite a slight decrease in perceived recovery. Long-term monitoring of the HR-RS index may help to predict positive adaptations, while interpretation of other recovery-related markers may need a more individualized approach.

This study aimed to examine the characteristics of electromyography (EMG) and kinematics of the supporting leg affecting energy cost while running at incline, level, and decline slopes. Twelve male Japanese middle- and long-distance runners volunteered for this study. The subjects were asked to run at 13.5 km·h -1 on a treadmill under three slope conditions. Sagittal plane kinematics and the EMG of the lower limb muscles, respiratory gases were recorded. Energy cost differed significantly between slopes, being the lowest in decline slope and the greatest in incline slope. Integrated EMG (iEMG) of leg extensor muscles was greater in the incline slope than in the decline slope, and iEMG of the gastrocnemius and soleus muscles correlated positively with energy cost. The knee and ankle joint kinematics were associated with energy cost during running. In incline slope, the knee and ankle joints were more extended (plantarflexed) to lift the body. These movements may disturb the coordination between the ankle and knee joints. The gastrocnemius muscle would do greater mechanical work to plantarflex the ankle joint rather than transfer mechanical energy as well as greater mechanical work of mono-articular muscles. These muscular activities would increase energy cost.

Skin and core tissue cooling modulates skeletal muscle oxygenation at rest. Whether tissue cooling also influences the skeletal muscle deoxygenation response during exercise is unclear. We evaluated the effects of skin and core tissue cooling on skeletal muscle blood volume and deoxygenation during sustained walking and running. Eleven male participants walked or ran six times on a treadmill for 60 min in ambient temperatures of 22°C (Neutral), 0°C for skin cooling (Cold 1), and at 0°C following a core and skin cooling protocol (Cold 2). Difference between oxy/deoxygenated haemoglobin ([diffHb]: deoxygenation index) and total haemoglobin content ([tHb]: total blood volume) in the vastus lateralis (VL) muscle was measured continuously. During walking, lower [tHb] was observed at 1 min in Cold 1 and Cold 2 vs. Neutral (P˂0.05). Lower [diffHb] was seen at 1 and 10 min in Cold 2 vs. Neutral by 13.5 ± 1.2 µM and 15.3 ± 1.4 µM and Cold 1 by 10.4 ± 3.1 µM and 11.1 ± 4.1 µM, respectively (P˂0.05). During running, [tHb] was lower in Cold 2 vs. Neutral at 10 min only (P = 0.004). [diffHb] was lower at 1 min in Cold 2 by 11.3 ± 3.1 µM compared to Neutral and by 13.5 ± 2.8 µM compared to Cold 1 (P˂0.001). Core tissue cooling, prior to exercise, induced greater deoxygenation of the VL muscle during the early stages of exercise, irrespective of changes in blood volume. Skin cooling alone, however, did not influence deoxygenation of the VL during exercise.

Purpose: To examine acute responses of force production and oxygen uptake to combined strength (S) and endurance-running (E) loading sessions in which the order of exercises is reversed (ES vs SE)., Methods: This crossover study design included recreationally endurance-trained men and women (age 21-45 y; n=12 men, 10 women) who performed ES and SE loadings. Force production of the lower extremities including countermovement-jump height (CMJ) and maximal isometric strength (MVC) was measured pre-, mid-, and post-ES and -SE, and ground-reaction forces, ground-reaction times, and running economy were measured during E., Results: A significant decrease in CMJ was observed after combined ES and SE in men (4.5%±7.0% and 6.6%±7.7%, respectively) but not in women (0.2%±8.5% and 1.4%±7.3% in ES and SE). MVC decreased significantly in both men (20.7%±6.1% ES and 19.3%±9.4% SE) and women (12.4%±9.3% ES and 11.6%±12.0% SE). Stride length decreased significantly in ES and SE men, but not in women. No changes were observed in ground-reaction times during running in men or women. Performing S before E caused greater (P<.01) oxygen uptake during running in both men and women than if E was performed before S, although heart rate and blood lactate were similar between ES and SE., Conclusions: Performing S before E increased oxygen uptake during E, which is explained, in part, by a decrease in MVC in both men and women, decreased CMJ and stride length in men, and/or an increase in postexercise oxygen consumption.

The study examined the acute neuromuscular and metabolic responses and recovery (24 and 48 h) to combined strength and endurance sessions (SEs). Recreationally endurance trained men (n = 12) and women (n = 10) performed: endurance running followed immediately by a strength loading (combined endurance and strength session (ES)) and the reverse order (SE). Maximal strength (MVC), countermovement jump height (CMJ), and creatine kinase activity were measured pre-, mid-, post-loading and at 24 and 48 h of recovery. MVC and CMJ were decreased (P < 0.05) at post-ES and SE sessions in men. Only MVC decreased in ES and SE women (P < 0.05). During recovery, no order differences in MVC were observed between sessions in men, but MVC and CMJ remained decreased. During recovery in women, a delayed decrease in CMJ was observed in ES but not in SE (P < 0.01), while MVC returned to baseline at 24 h. Creatine kinase increased (P < 0.05) during both ES and SE and peaked in all groups at 24 h. The present combined ES and SE sessions induced greater neuromuscular fatigue at post in men than in women. The delayed fatigue response in ES women may be an order effect related to muscle damage.

The purpose of the study was to examine the effects of an 8-week basic training (BT) with added strength training (ST) or endurance training (ET) on both the performance of a 3K-combat loaded run test and the acute neuromuscular and hormonal responses. All training groups improved (p < 0.001) their run-test times: ST by 12.4%, ET by 11.6%, and normal training (NT) by 10.2%. Significant acute decreases were observed in maximal isometric force of leg extensors (p < 0.01-0.05) in all subject groups following the run. Increases were observed in acute testosterone responses (p < 0.001) after the test in all groups both at pre- and post-training. However, ET and NT demonstrated lower (p < 0.001-0.05) acute post-training serum cortisol responses than ST. In conclusion, the present results indicate that within a demanding BT, the added training for ET and especially ST may be compromised in their adaptation potential due to interference from the demands of BT.

The aim of this study was to determine whether elite 1500-m runners differ in their running kinematics from national-standard 1500-m runners. Six national-standard male runners (seasonal best: 3 min 49.2 s +/- 3.2 s) were assessed during the second lap of a 1500-m race. Their running kinematics was then compared with those of five elite runners (seasonal best: 3 min 35.6 s +/- 2.6 s) analysed during the second lap of the men's 1500-m final at the 2005 World Championships. Data were collected using two high-speed cameras operating at 200 Hz with a three-dimensional pan and tilt system. Running speed was the same for both groups. Despite the similar contact times, the minimum knee angle during the stance phase was greater and the average extension velocity of the knee angle in the same phase slower in the elite runners than in the national-standard runners. In addition, the running technique of the elite runners appears to be characterized by a more efficient function of the hip joint. In conclusion, elite runners may utilize elastic energy more effectively, which, in combination with minimum concentric work, leads to improvements in their running performance.

The aim of this study was to examine the effects of muscle-tendon length on joint moment and power during maximal sprint starts. Nine male sprinters performed maximal sprint starts from the blocks that were adjusted either to 40 degrees or 65 degrees to the horizontal. Ground reaction forces were recorded at 833 Hz using a force platform and kinematic data were recorded at 200 Hz with a film camera. Joint moments and powers were analysed using kinematic and kinetic data. Muscle - tendon lengths of the medial gastrocnemius, soleus, vastus medialis, rectus femoris and biceps femoris were calculated from the set position to the end of the first single leg contact. The results indicated that block velocity (the horizontal velocity of centre of mass at the end of the block phase) was greater (P < 0.01) in the 40 degrees than in the 65 degrees block angle condition (3.39 +/- 0.23 vs. 3.30 +/- 0.21 m . s(-1)). Similarly, the initial lengths of the gastrocnemius and soleus of the front leg in the block at the beginning of force production until half way through the block phase were longer (P < 0.001) in the 40 degrees than in the 65 degrees block angle condition. The initial length and the length in the middle of the block phase were also longer in the 40 degrees than in the 65 degrees block angle condition both for both the gastrocnemius (P < 0.01) and soleus (P < 0.01-0.05) of the rear leg. In contrast, the initial lengths of the rectus femoris and vastus medialis of the front leg were longer (P < 0.05) in the 65 degrees than in the 40 degrees block angle condition. All differences gradually disappeared during the later block phase. The peak ankle joint moment (P < 0.01) and power (P < 0.05) during the block phase were greater in the 40 degrees than in the 65 degrees block angle condition for the rear leg. The peak ankle joint moment during the block phase was greater (P < 0.05) in the 40 degrees block angle for the front leg, whereas the peak knee joint moment of the rear leg was greater (P < 0.01) in the 65 degrees block angle condition. The results suggest that the longer initial muscle-tendon lengths of the gastrocnemius and soleus in the block phase at the beginning of force production contribute to the greater peak ankle joint moment and power and consequently the greater block velocity during the sprint start.

Electromyographic (EMG) activity of the leg muscles and the ground reaction forces were recorded in 17 elite male middle-distance runners, who performed isometric maximal voluntary contractions (MVC) as well as running at different speeds. Electromyograms were recorded from the gluteus maximus, vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior. The results indicated that the averaged EMG (aEMG) activities of all the muscles studied increased (P < 0.05) with increasing running speed, especially in the pre-contact and braking phases. At higher speeds, the aEMG activities of the gastrocnemius, vastus lateralis, biceps femoris and gluteus maximus exceeded 100% MVC in these same phases. These results suggest that maximal voluntary contractions cannot be used as an indicator of the full activation potential of human skeletal muscle. Furthermore, the present results suggest that increased pre-contact EMG potentiates the functional role of stretch reflexes, which subsequently increases tendomuscular stiffness and enhances force production in the braking and/or propulsive phases in running. Furthermore, a more powerful force production in the optimal direction for increasing running speed effectively requires increased EMG activity of the two-joint muscles (biceps femoris, rectus femoris and gastrocnemius) during the entire running cycle.

The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new "sine-wave" method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function,this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m.s-1 to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67 % to 6.93 % less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p < 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements.

The possible influence of increased eccentric mechanical work on the increase in oxygen uptake ( V(.)O(2)) after 3 min of running (Delta V(.)O(2)) was investigated through forward pulled running. Ten subjects ran at individually predetermined constant velocity on a treadmill, while being pulled forward. Ground reaction forces, expired gas and EMGs from leg muscles were collected after 3 min and at the end of the run. V(.)O(2) and mechanical work were then calculated. The amplitude of Delta V(.)O(2) was 138 (139) ml x min(-1) [mean (SD)]. Increased ventilation explained only 8% of Delta V(.)O(2). Stride frequency slightly decreased, inducing a similar decrease in internal work and total mechanical work (all P<0.01), while integrated EMG showed no modifications. It was concluded that Delta V(.)O(2) does not come from either an increase in mechanical work production or an increase in muscular activity. Delta V(.)O(2) could come from a lower muscle efficiency that could be due to a modification of fibre type recruitment.

The aim of this study was to test the suitability of inverse dynamics method for instantaneous expression of joint kinetics and muscle function with various parts of the ground contact when running at different speeds. Nine male runners ran at speeds of 4.0 m x s(-1), 6.0 m x s(-1) and at their maximal speed. 2-D video analysis (200-frame x s(-1)) was synchronized with 3-D ground reaction force measurements (10 m-long force platform). Mechanical joint power was computed from 2-D segment dynamics associated with joint forces and net moments in multi-body movements. From these computations two successive functional phases during contact were found in the ankle and knee joints: 1) extensor negative and 2) extensor positive work. The hip joint showed three phases: 1) extensor positive, 2) flexor negative and 3) flexor positive work. Peak joint power increased in every investigated joint with increasing running speed. The highest changes were observed in the hip joint: from 327 +/- 203 W at a speed of 4.0 m x s(-1) to 1642 +/- 729 W (p < 0.01) at the maximal speed. The results may suggest that the role of the ankle and knee extensors is to create high joint stiffness before and during the contact phase, while the hip extensors are the prime forward movers of the body with increasing running speed. In conclusion, the inverse dynamics method may be of importance for use in specifying the joint kinetics and muscle function. However, the interpretation may become clearer when this method is used simultaneously with EMG measurements.

Introduction: Stiffness has often been considered as a regulated property of the neuromuscular system. The purpose of this study was to examine the ankle and knee joint stiffness regulation during sprint running., Methods: Ten male sprinters ran at the constant relative speeds of 70, 80, 90, and 100% over a force platform, and ground reaction forces, kinematic, and EMG parameters were collected., Results: The results indicated that with increasing running speed the average joint stiffness (change in joint moment divided by change in joint angle) was constant (7 N x m x deg(-1)) in the ankle joint and increased from 17 to 24 N x m x deg(-1) (P < 0.01) in the knee joint., Conclusion: The observed constant ankle joint stiffness may depend on (constant) tendon stiffness because of its dominating role in triceps surae muscle-tendon unit. Thus, we conclude that in sprint running the spring-like behavior of the leg might be adjusted by changing the stiffness of the knee joint. However, in complicated motor task, such as sprint running, ankle and knee joint stiffness might be controlled by the individual mechanical and neural properties.

This study examined the predictive quality of intervals performed at maximal sustainable effort to predict 3-km and 10-km running times. In addition, changes in interval performance and associated changes in running performance were investigated. Either 6-week (10-km group, n=29) or 2-week (3-km group, n=16) interval training periods were performed by recreational runners. A linear model was created for both groups based on the running speed of the first 6×3-min interval session and the test run of the preceding week (T1). The accuracy of the model was tested with the running speed of the last interval session and the test run after the training period (T2). Pearson correlation was used to analyze relationships between changes in running speeds during the tests and interval sessions. At T2, the mean absolute percentage error of estimate for 3-km and 10-km test times were 2.3% and 3.4%, respectively. The change in running speed of intervals and test runs from T1 to T2 correlated (r=0.75, p<0.001) in both datasets. Thus, the maximal sustainable effort intervals were able to predict 3-km and 10-km running performance and training adaptations with good accuracy, and current results demonstrate the potential usefulness of intervals as part of the monitoring process. [ABSTRACT FROM AUTHOR]

Purpose. This study investigated the effects of two types of training on the bone formation marker of osteocalcin and the bone resorption marker of tartrate-resistant acid phosphatase isoenzyme 5b (trAP5b) in young track and field boys and girls. Methods. The 14-year-old group (10 boys, 10 girls) performed first time an intensive and supervised 8-week plyometric training. In the 17-year-old group (13 athletic boys, 6 control boys, 12 athletic girls, 6 control girls), the normal many-sided track and field training lasted 6 months. Results. Significant increases were noticed in osteocalcin (p < 0.01) both in younger boys and girls. The 20-m sprint performance improved in girls (p < 0.01) and the countermovement jump height increased in boys (p < 0.001). Significant increases in 17-year-old boys and girls were observed after training in osteocalcin (p < 0.01), osteocalcin/trAP5b ratio (p < 0.01 and p < 0.001), and the standing 5-jump (p < 0.05 and p < 0.01). Serum trAP5b decreased both in boys (p < 0.05) and in girls (p < 0.01). The boys also improved the standing 5-jump (p < 0.01) and the 12-minute running test results (p < 0.05). In the combined group of all subjects, the correlation coefficient between trAP5b and age was significant (r = --0.63, p < 0.001, n = 57). Conclusions. In practice, it is important to add plyometrics and other strength training in the training plans of young athletes, regardless of their events, to increase their bone metabolism and muscle strength. [ABSTRACT FROM AUTHOR]

The article reports on research which was conducted to investigate the impact that heat stress had on the physical performance and body composition of Finnish male soldiers during a four month deployment to a hot environment in Chad. Researchers evaluated 20 soldiers. They found that heat stress led to a decrease in body mass but found that the soldiers were able to maintain or improve their physical performance during the deployment despite the heat stress.

Forward pulled running on a treadmill is known to increase mechanical and decrease metabolic constrains relative to normal running. This experimental situation was used to investigate the variations of the mechanical parameters induced by the pulling. Ten subjects ran during 3 min at individually predetermined constant speeds of 16.4 ± 1.4 km ⋅ h[sup-1] on a treadmill while being forward pulled by a load equal to 5% of their body weight. Ground reaction forces were recorded during the last 30 s of the run. Kinematic parameters of the stride as well as impulses and mechanical work were then calculated. Stride frequency did not change, while horizontal impulses were highly modified (+38% and -28%, respectively, for the braking and pushing impulses). Simultaneously, external work produced during the braking and pushing phases was modified by +6.5% and -4.7%, respectively. Therefore, the horizontal impulses were far more modified than the mechanical work. As a consequence, the estimation of the relative influence of negative (braking) and positive (push-off) phases on metabolic cost of running could be quite different when forces, impulses, or work are considered. [ABSTRACT FROM AUTHOR]

Introduction: The physical fitness of male conscripts has decreased, and body mass increased during the last few decades, especially in Nordic countries. However, limited research-based reports are available concerning the physical fitness profiles of female recruits. Therefore, the purpose of this study was to investigate changes in physical fitness and body composition of female recruits entering voluntary Finnish military service between the years 2005 and 2015.Materials and methods: Data were collected from the initial fitness tests performed in military units during the first 2 weeks of military service. A total of 3,875 healthy female recruits (19.9 ± 2.1 year) participated in the fitness tests. Fitness tests consisted 12-minute running test and muscle fitness tests, which were sit-ups, push-ups, and standing long jump.Results: Increases in mean body mass (4.2%, p ≤ 0.01) and body mass index (3.8%, p < 0.01) were observed between 2005 and 2015. In addition, the proportion of overweight and obese female recruits increased by 12% (p ≤ 0.001). Mean endurance performance and overall muscle fitness remained unaltered during the study period, except for a decline in push-ups performance. However, the proportion of female recruits with poor endurance performance increased from 19.6% to 27.8% (p ≤ 0.001) between 2005 and 2015. Body mass was inversely associated with 12-minute running test distance (r = -0.35, p ≤ 0.001) and muscle fitness index (r = -0.25, p ≤ 0.001).Conclusions: In conclusion, the present study revealed that an increasing proportion of female recruits are overweight and/or have poor endurance performance, which are known risk factors for musculoskeletal injuries and premature discharge from military service. Therefore, specialized training programs should be designed specifically for female recruits with lower levels of fitness prior to military service. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the present study was to investigate changes in physical fitness and anthropometry of young men entering the military service in Finland during the years 1975-2015. Methods: The study included the fitness test results of 627,142 healthy young male conscripts (age 19.1 ± 0.4 yr). Data included results of aerobic capacity, muscle fitness tests, and anthropometric characteristics. Results: The results show that the increase in mean body mass of young men has slowed down during the last 10 yr. However, the total increase in body mass was 6.8 kg (8.8%, P ≤ 0.001) between 1993 and 2015. The mean distance achieved in the 12-min running test decreased by 337 m (12.2%, P ≤ 0.001) between the peak in 1980 and 2015. The relative number of conscripts who ran less than 2200 m increased from 3.6% to 25.9% (P ≤ 0.001) between 1980 and 2015, and the proportion who ran more than 3000 m decreased from 25.1% to 6.5% (P ≤ 0.001). The relative number of conscripts who achieved an excellent or good muscle fitness index decreased from 66.8% to 40.1% (P ≤ 0.001) between 1992 and 2000, and remained unchanged between 2000 and 2010. However, the proportion who achieved a poor muscle fitness index increased from 8.1% to 31.4% (P ≤ 0.001) between 1992 and 2010. Discussion: The present study shows that the increase in mean body mass of young male conscripts has slowed down during the last 10 yr. However, their aerobic capacity has still decreased during recent decades. In addition, the proportion of conscripts with poor muscle fitness has increased. From the national defense and health perspective, more initiatives are needed to encourage young men to increase their level of daily physical activity to be fit and ready for operations. [ABSTRACT FROM AUTHOR]