Sources of Variability in Iso-Inertial Jump Assessments

Abstract

Purpose:This investigation aimed to quantify the typical variation for kinetic and kinematic variables measured during loaded jump squats.Methods:Thirteen professional athletes performed six maximal effort countermovement jumps on four occasions. Testing occurred over 2 d, twice per day (8 AM and 2 PM) separated by 7 d, with the same procedures replicated on each occasion. Jump height, peak power (PP), relative peak power (RPP), mean power (MP), peak velocity (PV), peak force (PF), mean force (MF), and peak rate of force development (RFD) measurements were obtained from a linear optical encoder attached to a 40 kg barbell.Results:A diurnal variation in performance was observed with afternoon values displaying an average increase of 1.5–5.6% for PP, RPP, MP, PV, PF, and MF when compared with morning values (effect sizes ranging from 0.2–0.5). Day to day reliability was estimated by comparing the morning trials (AM reliability) and the afternoon trials (PM reliability). In both AM and PM conditions, all variables except RFD demonstrated coefficients of variations ranging between 0.8–6.2%. However, for a number of variables (RPP, MP, PV and height), AM reliability was substantially better than PM. PF and MF were the only variables to exhibit a coefficient of variation less than the smallest worthwhile change in both conditions.Discussion:Results suggest that power output and associated variables exhibit a diurnal rhythm, with improved performance in the afternoon. Morning testing may be preferable when practitioners are seeking to conduct regular monitoring of an athlete’s performance due to smaller variability.

Warm-Up Affects Diurnal Variation in Power Output

“…The improvements in the afternoon power and jump height are similar to previous research on time of day diff erences in jumping performance [6,26,28,30] . The novel fi nding from this study was that incorporating an extended, generalised warm-up period designed to increase body temperature equivalent to a normal whole body temperature experienced in the afternoon reduced the time of day diff erences in explosive neuromuscular performance.…”

“…Jump height was determined as the highest point on the displacement-time curve. High test-retest reliability has previously been established for this assessment protocol (coeffi cients of variation for all variables < 6 % ) [30] , while the validity and accuracy of the data collection procedures have been confi rmed using similar methodologies [8,11] .…”

“…Similarly, the current authors have recently shown that a time of day eff ect is characteristic of performance in a loaded counter-movement jump, with afternoon improvements of 4.3 -6.1 % in force, peak movement velocity and power output [30] . Although it is possible that the eff ect of time of day on muscle contractile properties could be attributed in part to intracellular variations in the muscle (e. g. a circadian variation in inorganic phosphate concentration [18] ), the more common hypothesis is that performance diff erences are causally related to the circadian rhythm in body temperature since previous researchers have observed a general parallelism between rhythms of physical performance and core temThe purpose of this study was to examine whether time of day variations in power output can be accounted for by the diurnal fl uctuations existent in body temperature.…”

Time Course of Improvements in Power Characteristics in Elite Development Netball Players Entering a Full-Time Training Program

“…Furthermore, senior elite volleyball players improved CMJ jump height by only 1.4% over a 12-month season (26). We contest that these results illustrate the potential for larger changes in performance for development athletes who have a "young" training age in terms of strength and power development as compared with a well-trained group of athletes who have many training years and their potential to improve is over smaller magnitudes in response to training interventions (13,14,28). We propose that the initial performance gains thus result from an underdeveloped neural adaptation in this athlete group, which is not ideal in regard to the physical age of the athletes as it would be preferred that this pathway for physical improvement is maximized before joining an end-of-development/subelite program.…”

Effect of airline travel on performance: a review of the literature

“…While a few studies and reviews have not supported this conclusion,7 8 circadian rhythmicity or time-of-day effects of various aspects of physical performance have been studied and the data suggest that significant effects are evident in many areas. These include leg strength,9–14 back strength,15 elbow flexors,16 jumping tasks,17 sprint and anaerobic efforts,18–20 and aerobic tasks 21 22. Sport-specific tasks such as soccer,23 cycling24–27 and swimming28 have also been shown to display rhythmicity.…”