Validity of spatiotemporal and ground reaction force estimates during resisted sprinting with a motorized loading device.

We aimed to examine the validity of estimating spatiotemporal and ground reaction force (GRF) parameters during resisted sprinting using a robotic loading device (1080 Sprint). Twelve male athletes (age: 20.9 ± 2.2 years; height: 174.6 ± 4.2 cm; weight: 69.4 ± 6.1 kg; means ± SDs) performed maximal resisted sprinting with three different loads using the device. The step frequency and length and step-averaged velocity, anteroposterior GRF (Fap ), and the ratio of Fap to resultant GRF (RF) were estimated using the velocity and towing force data measured using the device. Simultaneously, the corresponding values were measured using a 50-m force plate system. The proportional and fixed biases of the estimated values against those measured using the force plate system were determined using ordinary least product (OLP) regression analysis. Proportional and fixed biases were observed for most variables. However, the proportional bias was small or negligible except for the step frequency. Conversely, the fixed bias was small for step-averaged velocity (0.11 m/s) and step length (0.04 m), whereas it was large for step frequency (0.54 step/s), Fap (16N), and RF (2.22%). For all variables except step frequency, the prediction intervals in the OLP regression dramatically decreased when the corresponding values were smoothed using a two-step moving average. These results indicate that by using the velocity and force data recorded in the loading device, most of the spatiotemporal and GRF variables during resisted sprinting can be estimated with some correction of the fixed bias and data smoothing using the two-step moving average.

Influence of horizontal resistance loads on spatiotemporal and ground reaction force variables during maximal sprint acceleration.

This study aimed to elucidate the influence of horizontal resistance loads on the spatiotemporal and ground reaction force (GRF) variables during maximal sprint acceleration. Nine male sprinters (20.2 ± 1.2 years; 175.3 ± 4.5 cm, 69.7 ± 6.1 kg) performed sprint-running with six loading conditions of one unresisted and five resisted loads of 4, 6, 8, 10, and 12 kg using a resistance training device with intelligent drag technology. During the trials, the GRFs for all steps were determined using a 50-m force plate system. The spatiotemporal and GRF variables at running velocity of every 0.5 m/s were obtained and compared across the loading conditions. The maximal running velocity under 0, 4, 6, 8, 10, and 12 kg loading conditions were 9.84 ± 0.41, 8.55 ± 0.41, 8.09 ± 0.33, 7.62 ± 0.34, 7.11 ± 0.31, and 6.71 ± 0.29 m/s, respectively. ANOVA revealed significant main effects of load on the measured variables (η2 = 0.236-0.715, p < 0.05), except for stance-averaged anteroposterior GRF and braking impulse. However, the observed differences between the loading conditions were small, with approximately 4% (1.3-7.5%) for the GRF variables and approximately 9% (1.2-22.3%) for the spatiotemporal variables. The present study indicates that horizontal resistance load in sprint acceleration has little impact on the spatiotemporal and GRF variables at a given running velocity. In contrast to a general recommendation, one should adopt a heavy load in resisted sprint aiming to improve performance in the earlier stage of maximal sprint acceleration.

Measuring Muscle Activity in Sprinters Using T2-Weighted Magnetic Resonance Imaging.

PURPOSE: This study aimed to investigate the level of muscle activity during sprint running using T2-weighted magnetic resonance imaging. METHODS: Fourteen male sprinters (age 21.2 [4.0] y; height 171.8 [4.2] cm, weight 65.5 [5.3] kg, 100-m personal record 11.01 [0.41] s; mean [SD]) performed 3 sets of three 60-m round-trip sprints. Before and after the round-trip sprints, 3 T magnetic resonance imaging scans were performed to obtain the T2 values of the 14 athletes' lower-extremity muscles. RESULTS: After the 60-m round-trip sprints, the T2 value of the gluteus maximus, long head of biceps femoris, semitendinosus, semimembranosus, adductor brevis, adductor longus, adductor magnus, and gracilis increased significantly. The rate of change in the T2 values before and after the 60-m round-trip sprints was notably higher in the semitendinosus and gluteus maximus than in the other muscles. CONCLUSIONS: These findings demonstrate the specific physiological metabolism of the lower-extremity muscles during fast sprinting. There are particularly high levels of muscle activity in the gluteus maximus and semitendinosus during sprint performance.

Differences between junior and senior male sprinters in physiological variables associated with sprint performance.

BACKGROUND: The physiological variables associated with sprint performance have been extensively studied. However, little information is available on how the corresponding physiological variables differ between junior and senior sprinters. This study aimed to examine this subject. METHODS: In addition to the maximal running velocity achieved while sprinting over 60-m, body composition, muscle thicknesses of the trunk and lower limbs, performance scores of four jumping tasks (countermovement, rebound, standing long, and standing five-step jumps), and 10-s maximal anaerobic pedaling power were determined in 17 junior and 22 senior male sprinters. RESULTS: In the junior and senior sprinters, most of the measured variables were significantly correlated with the maximal running velocity. Analysis of covariance showed that only the maximal pedaling power relative to the body mass was significantly different between the two groups in the regression equation slope of the relationship with maximal running velocity (0.20 for junior and 0.64 for senior sprinters). Additionally, multiple regression analysis revealed that while the standing five-step jump distance (40%) and the size of the psoas major muscle (23%) were selected as explanatory factors for maximal running velocity in the junior sprinters, maximal pedaling power relative to the body mass (63%) was selected in the senior sprinters. CONCLUSIONS: This study suggests that the following physiological factors associated with sprint running performance differ between the junior and senior sprinters: the ability of repetitive jumping in the horizontal forward direction and muscularity of hip flexors in the junior sprinters versus the anaerobic capacity in senior sprinters. Therefore, coaches and athletes need to take into consideration that the physiological variables to be focused on are different for each generation.

Ten-second maximal pedaling power as a representative measure for assessing sprint performance.

BACKGROUND: There is no evidences concerning the relative contribution of physiological parameters to maximal sprinting velocity and acceleration ability. The aim of this study is to elucidate the associations between physiological variables and sprint performance. METHODS: Twenty-six male sprinters performed a 60-m sprint twice. Maximal sprint velocity (Vmax) and running distance after 4 s from the start (D4) were measured as indices of sprint performance during the sprint using a laser distance measurement device. Body composition, jump performance in the countermovement jump, the rebound jump, the standing long jump and the standing 5-step jump, and 10-s maximal anaerobic pedaling power were measured as physiological variables. RESULTS: All measured variables were significantly related to Vmax (r=0.49-0.71, P<0.05) and D4 (r=0.39-0.72, P<0.05), expect for anthropometric variables. Multiple regression analysis indicated that the 10-s maximal anaerobic pedaling power relative to body mass was the only variable that significantly explained Vmax and D4. CONCLUSIONS: The 10-s maximal anaerobic pedaling power relative to body mass can be a representative measure for assessing the sprint performance of male sprinters.

Cardiorespiratory and metabolic responses to body mass-based squat exercise in young men.

BACKGROUND: The purpose of this study was to quantify cardiorespiratory and metabolic responses to body mass-based squat exercise, with specific emphasis on the relationships with the exercise duration. METHODS: Fifteen healthy young men performed body mass-based squat exercise as well as an incremental loaded bicycle test, which determine maximal oxygen uptake and maximal heart rate, with an interval of 2 days between the tests. During both tasks, oxygen uptake, blood lactate concentration (BLa), and heart rate (HR) were determined. Oxygen uptake in both tasks was divided by body mass (VO2). VO2 in the squat task was normalized to VO2 in the incremental test (%VO2max). In addition, electromyograms (EMGs) were also recorded from the vastus lateralis, rectus femoris, vastus medialis, biceps femoris, and gluteus maximus. RESULTS: Cardiorespiratory parameters and BLa did not change after 5 min from the exercise onset. The %VO2max and BLa during body mass-based squat exercise were significantly related to maximal VO2 obtained by the incremental test. Metabolic equivalents reached 6.5 when the squat exercise was continuously performed for 5 min. CONCLUSIONS: These findings indicate that (1) the squat exercise adopted here is of moderate intensity and predominantly uses aerobic energy supply after 5 min from the start of the exercise and (2) relative intensity during the exercise depends on an individual's maximal aerobic power.

Acute effects of different conditioning activities on running performance of sprinters.

This study investigated acute effects of different conditioning activities on sprint performance of collegiate sprinters using a randomized, crossover design. Male sprinters (N = 10; 20.1 ± 0.6 years; 174.6 ± 4.4 cm; 66.7 ± 3.5 kg; 100-m race personal best time, 11.46 ± 0.57 s; means ± SDs) performed two 60-m sprints and one of three treatments within the same day, with an interval of 2 days between the treatments. The baseline sprint was followed by one of three different conditioning activities: mini-hurdles, bounding jumps, or a free sprint. Participants then performed the post treatment sprint. In the mini-hurdle drill, the participants ran over 10 × 10 mini-hurdles (height 22 cm) as fast as possible. In the bounding jump drill, the participants performed three 60-m bounding jumps as explosively and far as possible, with 3 min intervals between trials. In the free-sprint conditioning activity, the participants performed a 60-m maximal sprint twice, with a 5 min interval between sprints. Sprint kinematics in the baseline and post treatment sprints were recorded using a high-speed camera (300 Hz). Using these films, sprint time, running velocity, step length, and step frequency were analyzed over 10 m intervals. The results of ANOVAs indicated that the mini-hurdle drill increased the maximal sprint velocity (3.2 %) and maximal step frequency (3.3 %); the other conditioning activities had no such effects. Step length did not change after any of the conditioning activities. These results suggest that conditioning activities with mini-hurdles, which require movements with a high step frequency, acutely enhances velocity during sprinting, possibly as a result of increasing step frequency.

Effects of school-based squat training in adolescent girls.

BACKGROUND: For adolescent girls, less information on the effects of school-based exercise training is available from earlier studies. This study aimed to determine the effects of school-based squat training on body composition and muscular strength in adolescent girls. METHODS: Fifty-two girls (13.8±0.6 years) were randomly assigned to the training and control groups. The training group conducted an 8-week body mass-based squat exercise training (100 reps/day, 45 sessions) as a part of after-school activity. Body composition (bioelectrical impedance analyzer), muscle thickness at the thigh anterior (ultrasound), and maximal isometric knee extension strength (myometer) were determined before and after the intervention. The magnitude of maturation was assessed using Tanner stage criteria of pubic hair before the intervention. RESULTS: After the intervention, percent body fat decreased in the training group, but increased in the control group. The relative changes in lean body mass, muscle thickness and muscular strength were similar between both groups. In the training group, the relative change in knee extension strength was correlated to the magnitude of maturation before the intervention. CONCLUSIONS: For adolescent girls, an 8-week body mass-based squat training is feasible for lowering percent body fat. In addition, the strength improvement for the knee extensors partially depends on the magnitude of maturation at start of the intervention.

Effect of maturation on muscle quality of the lower limb muscles in adolescent boys.

BACKGROUND: The purpose of this study was to clarify the effect of maturation on the muscle quality of the lower limb muscles around puberty. METHODS: Subjects were 117 Japanese boys age 12 to 15 years. The maturity status was assessed by using a self-assessment of stage of pubic hair development based on the criteria of Tanner. On the basis of the criteria, subjects were divided into the prepubescent or pubescent group. Muscle thickness of knee extensors and plantar flexors were measured by a B-mode ultrasound. Muscle volume index (MV) was calculated from muscle thickness and limb length. Maximal voluntary isometric joint toques (TQ) of knee extension and ankle plantar flexion were measured using a myometer. Muscle quality was derived from dividing TQ by MV (TQ/MV). RESULTS: In both muscles, TQ-MV relationships were also similar between the prepubescent and pubescent groups, and there was no significant difference in TQ/MV between the two groups when chronological age was statistically adjusted. CONCLUSION: The current results indicate that, for adolescent boys, the muscle quality of the lower limb muscles is not significantly influenced by maturation.

Effects of body mass-based squat training in adolescent boys.

The purpose of this study was to determine the effects of body mass-based squat training on body composition, muscular strength and motor fitness in adolescent boys. Ninety-four boys (13.7 ± 0.6 yrs, 1.60 ± 0.09 m, 50.2 ± 9.6 kg) participated in this study and were randomly assigned to training (n = 36) or control (n = 58) groups. The training group completed body mass-based squat exercise training (100 reps/day, 45 sessions) for 8 weeks. Body composition and muscle thickness at the thigh anterior were determined by a bioelectrical impedance analyzer and ultrasound apparatus, respectively. Maximal voluntary knee extension strength and sprint velocity were measured using static myometer and non-motorized treadmill, respectively. Jump height was calculated using flight time during jumping, which was measured by a matswitch system. The 8-wk body mass-based squat training significantly decreased percent body fat (4.2%) and significantly increased the lean body mass (2.7%), muscle thickness (3.2%) and strength of the knee extensors (16.0%), compared to control group. The vertical jump height was also significantly improved by 3.4% through the intervention. The current results indicate that body mass-based squat training for 8 weeks is a feasible and effective method for improving body composition and muscular strength of the knee extensors, and jump performance in adolescent boys. Key pointsAn 8-wk body mass-based squat exercise training decreased percent body fat in adolescent boys.The body mass-based squat exercise training increased muscle size and strength capability of the knee extensors in adolescent boys.The squat exercise training improves vertical jump height in adolescent boys.

Influence of maturation on anthropometry and body composition in Japanese junior high school students.

BACKGROUND: The purpose of this study was to examine maturity-related differences in anthropometry and body composition in Japanese youth within a single year. METHODS: Two hundred and ten Japanese youth aged from 13 to 13.99 years participated in this study. Their maturity status was assessed using a self-assessment of stage of pubic hair development. Bioelectrical impedance analysis was used to estimate percent body fat and lean body mass (LBM). Muscle thickness of the anterior thigh, posterior lower leg and rectus abdominis muscles were measured by ultrasound. RESULTS: For boys, height, body weight, and LBM in less mature groups were lower than that in more mature groups. The maturity-related differences were still significant after adjusting for chronological age. On the other hand, muscle thickness values in the lower extremity and abdomen differed among the groups at different stages of pubic hair development, whereas there was no maturity-related difference in the relative values corrected by LBM, except for those thickness values measured at the abdomen. For girls, only the muscle thickness at the anterior thigh and muscle thickness relative to LBM1/3 at the posterior lower leg was significantly affected by maturity status, but significant maturity-related difference was not found after adjusting for chronological age. CONCLUSIONS: At least for Japanese boys and girls aged 13 years, maturity status affected body size in boys, but not in girls, and the influence of maturation on the muscularity of the lower extremity and trunk muscles is less in both sexes.