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Introduction Diurnal variations in physical performance can affect athletes' success in competitive sports depending on whether the time of peak performance concurs with the time of competition. The purpose of this systematic review was to investigate the diurnal variation in maximum endurance and strength performance. Methods The databases PubMed, EMBASE, and Web-of-Science were searched from inception to November 2020. The search string was externally reviewed according to PRESS guidelines, the review was conducted in accordance to PRISMA guidelines, and registered beforehand on PROSPERO. Eligibility criteria were that [1] the studies included humans, [2] any kind of maximum endurance or maximum strength test was performed at [3] a minimum of three different times of the day. There were no restrictions regarding study design, participants' sex, age or fitness levels. Results From 10,460 screened articles 63 articles met all three inclusion criteria. Meta-analysis on the harmonizable 29 studies provided evidence for diurnal variations in physical performance. In detail, the overall effect sizes (95% confidence intervals) were 0.23 (0.05; 0.40), 0.73 (0.37; 1.09), 0.39 (0.18; 0.60), and 0.79 (0.28, 1.30) for endurance exercise tests, maximum power output in Wingate-test, handgrip strength, and jump height all in favor of higher performance in the evening. The overall risk of bias in individual studies was moderately high. Conclusions There is strong evidence that anaerobic power as well as jump height are maximal between 13:00 and 19:00. There is some evidence that handgrip strength peaks between 13:00 and 21:00, but only little evidence that there is a time of peak performance in maximum endurance.

AB Purpose: The aim of this study was to investigate the muscle strength and arch height of the foot in the standing position and the relations between these indices and physical performances involving the lower limbs in children. Methods: A total of 301 elementary school children (third grade: n = 158, age = 8.6 +/- 0.5 yr; fifth grade: n = 143, age = 10.6 +/- 0.5 yr; means +/- SD) participated. The maximal isometric toe flexor strength (TFS) in the standing position was measured using a toe flexor dynamometer. Foot arch height was assessed as the distance between the navicular tuberosity of the foot and the floor in the standing position, and foot arch height relative to the foot length was represented by the foot arch index (FAI). For physical performance involving the lower limbs, 50-m sprint, standing broad jump, repeated side step, and rebound jump were measured. Results: There were no significant correlations between TFS and FAI and between relative TFS (relative TFS = TFS/body mass) and FAI. Relative TFS was significantly correlated with all physical performance tests. No significant correlations among FAI and physical performances were found, except for rebound jump ability in fifth graders. After multiple regression analyses adjusting for gender and body mass, TFS was the only significant correlating factor for all physical performances involving the lower limbs. Conclusions: This study showed that TFS was associated with enhancement of some measures of lower limb physical performance in children. These results suggest that foot function should be evaluated with both the muscle strength and arch height of the foot in children

Purpose: Less lean body mass may limit one’s ability to produce adequate muscle forces to safely control landing from a jump, thus increasing the risk for injury. The primary objective of this study was to determine the effect of lower extremity lean mass (LELM) and eccentric muscle strength on lower extremity energy absorption (EA) during a drop jump landing.Methods: Seventy athletic subjects (35 men and 35 women) were measured for LELM with dual-energy x-ray absorptiometry, maximal eccentric strength of the quadriceps (QuadECC) and hamstrings (HamECC), and lower extremity joint energetics during the initial landing of a drop jump. A mediation analysis examined the extent to which LELM predicted EA at each lower extremity joint (EAHIP, EAKNEE, and EAANK) and subsequently whether these relationships were mediated by each subject’s maximal eccentric strength capabilities.Results: LELM was a significant predictor of EAKNEE (R2 = 0.22, P < 0.01) in females but not in males (R2 = 0.03, P = 0.16). In females, QuadECC was a significant mediator of the effect of LELM on EA at the knee (ab = 179.72, 95% confidence interval [CI] = 10.43–423.42) and ankle (ab = 1.71, 95% CI = [0.16, 3.94]), whereas HamECC was a significant mediator of the relationship between LELM and EAHIP (ab = 4.89, 95% CI = 2.05–8.40). No significant relationships were observed in males.Conclusions: LELM was a significant factor in energetic capabilities for females but not males. For females, this relationship was evident secondary to the stronger underlying relationship between maximal strength and EA. Thus, the maximal eccentric strength capabilities may be a more important determinant of energetic behaviors compared with the available quantity of lean mass alone. More work is needed to investigate these relationships and to reveal the underlying sex-specific mechanisms that determine EA capabilities.

Purpose: To determine whether ballistic power training and strength training result in specific changes in stretch-shorten cycle (SSC) function during the eccentric (ECC) phase and, if so, whether these changes are influenced by the individual's strength level. Methods: Thirty-two male subjects were divided into four groups: stronger power training group (SP, n = 8, squat one-repetition maximum-to-body mass ratio (1RM/BM) = 1.97 ± 0.08), weaker power training group (WP, n = 8, 1RM/BM = 1.32 ± 0.14), weaker strength training group (WS, n = 8, 1RM/BM = 1.28 ± 0.17), or control group (C, n = 8, 1RM/BM = 1.37 ± 0.13). Training involved three sessions per week for 10 wk. The SP and WP groups performed maximal-effort jump squats with 0%-30% 1RM, and the WS group performed back squats at 75%-90% 1RM. Maximal strength, jump performance, musculotendinous stiffness, and neural activation were assessed before training and after 5 and 10 wk of training. Results: Both power and strength training elicited significant changes in a multitude of ECC variables that were significantly associated with improvements in concentric (CON) performance. Enhancements in CON performance were theorized to be driven by the development of a strategy to better use the ECC phase during jumping (i.e., greater unloading allowed for increased negative acceleration and thus velocity during the countermovement and improved musculotendinous stiffness resulted in an enhanced ability to translate the momentum developed during the ECC phase into force). Although a significant improvement in maximal strength resulted in changes to SSC function during the ECC phase, the initial strength level did not significantly affect the ECC variables before training or the magnitude of adaptations in individuals exposed to ballistic power training. Conclusions: Training-induced alterations in SSC function during the ECC phase contributes to improvements in jump performance after both ballistic power training and heavy strength training.

Purpose: To determine whether the magnitude of performance improvements and the mechanisms driving adaptation to ballistic power training differ between strong and weak individuals. Methods: Twenty-four men were divided into three groups on the basis of their strength level: stronger (n = 8, one-repetition maximum-to-body mass ratio (1RM/BM) = 1.97 +/- 0.08), weaker (n = 8, 1RM/BM = 1.32 +/- 0.14), or control (n = 8, 1RM/BM = 1.37 +/- 0.13). The stronger and weaker groups trained three times per week for 10 wk. During these sessions, subjects performed maximal-effort jump squats with 0%-30% 1RM. The impact of training on athletic performance was assessed using a 2-d testing battery that involved evaluation of jump and sprint performance as well as measures of the force-velocity relationship, jumping mechanics, muscle architecture, and neural drive. Results: Both experimental groups showed significant (P