Changes in Loaded Countermovement Jumps During Precompetition and Competition Training Mesocycles in Elite Rowers.

ABSTRACT: Everett, KLA, Chapman, DW, Mitchell, JA, and Ball, N. Changes in loaded countermovement jumps during precompetition and competition training mesocycles in elite rowers. J Strength Cond Res 36(9): 2622-2627, 2022-To assess changes in velocity, displacement, and power as an indicator of neuromuscular fatigue (NMF) within and between precompetition and competition mesocycles in elite male rowers using loaded countermovement jumps (CMJs). Twenty highly trained rowers completed regular training (on-water rowing, rowing ergometer, and resistance training sessions) in 2 consecutive mesocycles. Athletes completed a single set of 6 loaded (20 kg) CMJs in the first and final week of each mesocycle. Countermovement jumps were assessed for jump height (JH), eccentric displacement, mean velocity (MV), eccentric MV (EMV), and mean power. Changes between time points were reported as Cohen's d effect sizes (95% confidence interval [CI]). The magnitude of the differences was also considered based on their relative strength levels using a linear mixed model. Within the precompetition mesocycle, trivial-to-small reductions for all variables (0.5-4.1%) were observed. During the competition mesocycle, trivial-to-small increases were shown for EMV (1.4%) and eccentric displacement (2.0%) with no change in JH and small reductions in MV (0.5%) and mean power (2.8%). No differences between the precompetition and competition mesocycles were shown. Only mean power showed a significant reduction in weaker athletes (3.2%) compared with stronger athletes (2.3%). Training completed during a precompetition and competitive mesocycle did not result in significant decreases in athlete's loaded CMJ performance, indicating that NMF was minimized. Alternatively, use of a loaded CMJ may not be sensitive enough to observe NMF in elite rowers during the mesocycle immediately leading into and during a competition mesocycle.

Effects of Westbound Trans-meridian Travel on Countermovement Jump Performance in International-Level Rowers.

ABSTRACT: Everett, KLA, Chapman, DW, Mitchell, JA, and Ball, N. Effects of westbound trans-meridian travel on countermovement jump performance in international-level rowers. J Strength Cond Res 36(7): 1961-1965, 2022-International long-haul air travel is a necessity for many athletes as part of their training or competition schedules. However, long-haul travel is also associated with impaired neuromuscular function. An athlete's lower body neuromuscular status is frequently assessed and monitored using countermovement jump (CMJ). This study assessed the impact of westbound trans-meridian travel on changes in CMJ performance in highly trained aerobic athletes. Highly trained male rowers (n = 21, 23.7 ± 1.4 years, 1.91 ± 0.07 m, 86.9 ± 9.9 kg) undertook a westbound flight incurring 22 hours of flight time with 30 hours of total travel time across 9 time zones. Athletes completed a single set of 6 loaded CMJ repetitions before and after travel with performance measured using a digital optical encoder attached to a 20 kg barbell. Each CMJ repetition was assessed for mean concentric velocity, jump height (JH), eccentric displacement, JH:dip ratio, mean power, and mean eccentric velocity, with comparisons made between mean set changes before and after travel. Changes were compared using a one tail paired t-test and characterized using Cohen's d (95% confidence interval) effect sizes. Significance was accepted at p ≤ 0.05. Small-to-moderate changes were observed in all variables following westbound travel. These changes may be because of retention of high training loads before travel resulting in the athletes being in a fatigued state, whereas travel time worked as a forced recovery period. Reductions in CMJ performance are likely following westbound travel, however, may be affected by training fatigue before travel that may confound CMJ performance as a monitoring metric.

Responses of Lower-Body Power and Match Running Demands Following Long-Haul Travel in International Rugby Sevens Players.

Mitchell, JA, Pumpa, KL, and Pyne, DB. Responses of lowerbody power and match running demands after long-haul travel in international rugby sevens players. J Strength Cond Res 31(3): 686-695, 2017-This study determined the effect of long-haul (>5 hours) travel on lower-body power and match running demands in international rugby sevens players. Lower-body power was assessed in 22 male international rugby sevens players (age 21.7 ± 2.7 years, mass 89.0 ± 6.7 kg, stature 180.5 ± 6.2 cm; mean ± SD) monitored over 17 rugby sevens tournaments. A countermovement jump was used to monitor lower-body power (peak and mean power) over repeated three week travel and competition periods (pretravel, posttravel, and posttournament). Small decreases were evident in peak power after both short and long-haul travel (-4.0%, ±3.2%; mean, ±90% confidence limits) with further reductions in peak and mean power posttournament (-4.5%, ±2.3% and -3.8%, ±1.5%) culminating in a moderate decrease in peak power overall (-7.4%, ±4.0%). A subset of 12 players (completing a minimum of 8 tournaments) had the effects of match running demands assessed with lower-body power. In this subset, long-haul travel elicited a large decrease in lower-body peak (-9.4%, ±3.5%) and mean power (-5.6%, ±2.9%) over the monitoring period, with a small decrease (-4.3%, ±3.0% and -2.2%, ±1.7%) posttravel and moderate decrease (-5.4%, ±2.5% and -3.5%, ±1.9%) posttournament, respectively. Match running demands were monitored through global positioning system. In long-haul tournaments, the 12 players covered ∼13%, ±13% greater total distance (meter) and ∼11%, ±10% higher average game meters >5 m·s when compared with short-haul (<5 hours) travel. Effective pretravel and posttravel player management strategies are indicated to reduce neuromuscular fatigue and running load demands in rugby sevens tournaments after long-haul travel.

Variable Changes in Body Composition, Strength and Lower-Body Power During an International Rugby Sevens Season.

This study determined whether body composition, strength, and power changes that occur during preseason can be maintained during an international rugby sevens season. Fourteen male international rugby sevens players (age 21.4 ± 2.2 years; mean ± SD) were categorized as forward (n = 7) or back (n = 7), and assessed for height, mass (M), skinfolds (S) (∑7), upper-body (UB) strength, lower-body (LB) strength, and LB power. Bench press, back squat, and a countermovement jump were used to measure strength and power at 3 time points: initial, early season, and late season. Forwards were taller (185 ± 4 cm), heavier (95 ± 6 kg), and possessed a greater lean body mass (55.5 ± 4.0 M·S) than backs (181 ± 8 cm, 88.5 ± 5.5 kg, and 51.9 ± 3.4 M·S). Over the full season, small (∼5 ± 5%; mean ± 90% confidence limits) positive changes occurred in body composition. Lower-body strength gained during the preseason, decayed in-season, whereas UB strength increased moderately (∼10 ± 3%) across the season. Power showed inconsistencies between measured variables with a moderate positive change across the season in mean velocity and relative peak power. Forwards showed a small decrease in peak power (relative and absolute). Moderate changes were observed in mean power over the season, forwards decreasing (∼6 ± 6%) and backs increasing (∼8 ± 6%). Rugby sevens forwards in this study found it difficult to maintain and improve power qualities in-season. Training loads of forwards and backs should be differentiated to maximize strength and power in-season.

Mechanical properties of zirconium alloys and zirconium hydrides predicted from density functional perturbation theory.

The elastic properties and mechanical stability of zirconium alloys and zirconium hydrides have been investigated within the framework of density functional perturbation theory. Results show that the lowest-energy cubic Pn3[combining macron]m polymorph of δ-ZrH1.5 does not satisfy all the Born requirements for mechanical stability, unlike its nearly degenerate tetragonal P42/mcm polymorph. Elastic moduli predicted with the Voigt-Reuss-Hill approximations suggest that mechanical stability of α-Zr, Zr-alloy and Zr-hydride polycrystalline aggregates is limited by the shear modulus. According to both Pugh's and Poisson's ratios, α-Zr, Zr-alloy and Zr-hydride polycrystalline aggregates can be considered ductile. The Debye temperatures predicted for γ-ZrH, δ-ZrH1.5 and ε-ZrH2 are θD = 299.7, 415.6 and 356.9 K, respectively, while θD = 273.6, 284.2, 264.1 and 257.1 K for the α-Zr, Zry-4, ZIRLO and M5 matrices, i.e. suggesting that Zry-4 possesses the highest micro-hardness among Zr matrices.

A simulated-use evaluation of a strategy for preventing biofilm formation in dental unit waterlines.

BACKGROUND: Prevention of biofilm formation is important in the maintenance of dental unit waterline systems. Without effective control measures, the waterlines will become contaminated with routine use. METHODS: The authors used a simulated-use dental unit waterline system to evaluate the ability of a test product, A-dec ICX (A-dec, Newburg, Ore.), to prevent biofilm formation. They evaluated buffered distilled water and hard water models versus mixed-challenge suspensions of Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa. RESULTS: The authors documented development of significant biofilm in untreated test units, while treated test units showed no indication of biofilm formation throughout the 16-week study. Student t tests and 95 percent confidence intervals performed on the plate count data confirmed that untreated test units had significantly greater bacterial populations than did treated test units (P < .05). Qualitative images by scanning electron microscopy verified these findings. CONCLUSION: In this simulated clinical-use study, the test product effectively reduced bacterial counts in incoming water and produced water quality exceeding stated recommendations of the American Dental Association. CLINICAL IMPLICATIONS: The test product provides an approach to dental unit waterline maintenance that is simple to use and that, by continuously preventing biofilm formation, reduces concerns about bacterial contamination in dental unit water.