Following a bout of high-intensity exercise of short duration (preload stimulus), the muscle is in both a fatigued and a potentiated (referred to as postactivation potentiation) state. Consequently, subsequent muscle performance depends on the balance between these 2 factors. To date, there is no uniform agreement about the optimal recovery required between the preload stimulus and subsequent muscle performance to gain optimal performance benefits. The aim of the present study was to determine the optimal recovery time required to observe enhanced muscle performance following the preload stimulus. Twenty-three professional rugby players (13 senior international players) performed 7 countermovement jumps (CMJs) and 7 ballistic bench throws at the following time points after a preload stimulus (3 repetition maximum [3RM]): baseline, approximately 15 seconds, and 4, 8, 12, 16, and 20 minutes. Their peak power output (PPO) was determined at each time point. Statistical analyses revealed a significant decrease in PPO for both the upper (856 +/- 121 W vs. 816 +/- 121 W, p < 0.001) and the lower (4,568 +/- 509 W vs. 4,430 +/- 495 W, p = 0.005) body when the explosive activity was performed approximately 15 seconds after the preload stimulus. However, when 12 minutes was allowed between the preload stimulus and the CMJ and ballistic bench throws, PPO was increased by 8.0 +/- 8.0% and 5.3 +/- 4.5%, respectively. Based on the above results, we conclude that muscle performance (e.g., power) can be significantly enhanced following a bout of heavy exercise (preload stimulus) in both the upper and the lower body, provided that adequate recovery (8-12 minutes) is given between the preload stimulus and the explosive activity.

There is a general agreement that the most valid method of measuring peak lower-body mechanical power output (LBPP) in a countermovement jump (CMJ) is by analysis of the corresponding vertical component of the ground reaction force (VGRF)-time history of the jump. However, there is no published standard protocol. The purpose of this study was to establish a standard protocol. The variables necessary to define a valid and reliable CMJ method were: (a) vertical force range, (b) force sampling and integration frequency, (c) method of integration, (d) determination of body weight (BW), and (e) determination of the initiation of the CMJ. Countermovement jumps off a force platform (FP) were performed by 15 male professional rugby players. The 5 variables were then optimized to maximize the reliability and validity of the measure of LBPP. Errors of <1% (p ≤ 0.05) in the measurement of LBPP were obtained using the following specification: (a) 6 times BW (using a 16-bit analog to digital converter), (b) 1,000 Hz, (c) Simpson's rule or the trapezoidal rule, (d) mean VGRF for 1 second of quiet standing immediately before jump signal, and (e) 30 ms before the instant BW ± 5 SD is exceeded after the jump signal. Peak lower-body power output was most sensitive to variables 4 and 5. It was concluded that this study has established a standard protocol for the criterion method of measuring peak power in a CMJ using an FP. As all other estimates and less reliable methods of determining LBPP in a CMJ rely on the FP method for calibration, it is proposed that this protocol be used as the basis of future criterion measures using a FP.

Digit ratio (2D:4D) denotes the relative length of the second and fourth digits. This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental animals, via amniotic fluid samples and in the study of sex-typical traits) in relation to 2D:4D. In contrast, the relationships between 2D:4D and levels of sex steroids in adults are less clear, as many correlational studies of 2D:4D and adult sex steroids have concluded that this association is statistically non-significant. Here, we suggest that in order to understand the link between 2D:4D and sex hormones, one must consider both fetal organizing and adult activating effects of T and E. In particular, we hypothesize that 2D:4D correlates with organizing effects on the endocrine system that moderate activating effects in adulthood. We argue that this is particularly evident in “challenging” conditions such as aggressive and sexual encounters, in which individuals show increased levels of T. We discuss this refinement of the 2D:4D paradigm in relation to the links between 2D:4D and sports performance, and aggression.

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