Zubac, D and Šimunič, B. Skeletal muscle contraction time and tone decrease after 8 weeks of plyometric training. J Strength Cond Res 31(6): 1610–1619, 2017—The aim of the study was to examine whether an improvement in jumping performance after 8 weeks of plyometric training (PT) runs in parallel with changes in lower-limb skeletal muscle contractile properties. Using noninvasive tensiomyography (TMG), we assessed contraction time (Tc) and the maximal amplitude of radial displacement (Dm) in 20 subjects (50% men; age 22.4 ± 4.7 years of age), randomly divided in PT group (N = 10; PLYO) and a control group (N = 10; CTRL). The PLYO performed 8 weeks of PT. Tensiomyography was measured in 5 leg skeletal muscles: vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), gastrocnemius medialis (GM), and gastrocnemius lateralis (GL). Additionally, we evaluated countermovement jump (CMJ) height improvement on a ground force plate. Assessments were repeated before and after PT. After 8 weeks of PT, CMJ height increased by 12.2% in PLYO (p = 0.015), but not in CRTL. Contraction time, which is related to myosin heavy-chain type 1 (MHC-1) proportion, decreased in VL (−8.7%; p < 0.001), BF (−26.7%; p = 0.032), TA (−32.9%; p = 0.004), and GL (−25.8%; p = 0.044), but not in GM (−8.1%; p = 0.158). The estimated VL MHC-1 proportion decreased by −8.2% (p = 0.041). The maximal amplitude of radial displacement, inversely related to muscle tone, decreased in BF (−26.5%; p = 0.032), GM (−14.9%; p = 0.017), GL (−31.5%; p = 0.017), but not in TA (−16.8%; p = 0.113) and VL (−6.0%; p = 0.654). After PT, jumping performance increased, which was paralleled by decreased Tc and decreased muscle tone. Additionally, adaptations to contractile properties were muscle specific, which is important for future studies. It seems that adjustments were dose dependent, being higher in muscles with lower habitual load.

Urine specific gravity (U_SG) is the most commonly reported biochemical marker used in research and applied settings to detect fluid deficits in athletes, including those participating in combat sports. Despite the popularity of its use, there has been a growing debate regarding the diagnostic accuracy and the applicability of U_SG in characterizing whole‐body fluid status and fluctuations. Moreover, recent investigations report universally high prevalence of hypohydration (∼90%) via U_SG assessment in combat sport athletes, often in spite of stable body‐mass. Given the widespread use in both research and practice, and its use in a regulatory sense as a ‘hydration test’ in combat sports as a means to detect dehydration at the time of weigh‐in; understanding the limitations and applicability of U_SG assessment is of paramount importance. Inconsistencies in findings of U_SG readings, possibly as a consequence of diverse methodological research approaches and/or overlooked confounding factors, preclude a conclusive position stand within current combat sports research and practice. Thus the primary aim of this paper is to critically review the literature regarding U_SG assessment of hydration status in combat sports research and practice. When taken on balance, the existing literature suggests: the use of laboratory derived benchmarks in applied settings, inconsistent sampling methodologies, the incomplete picture of how various confounding factors affect end‐point readings, and the still poorly understood potential of renal adaptation to dehydration in combat athletes; make the utility of hydration assessment via U_SG measurement quite problematic, particularly when diet and training is not controlled.

Purpose:To examine the influence of rapid weight loss (RWL) on competitive success in elite youth Olympic-style boxers. In addition, this study examined the practice and prevalence of weight reduction, weight-management protocols, and related symptoms in youth boxers from 12 European countries (N = 83, all males, mean [SD] age 17.1 [0.9] y).Methods:The data were collected using an extensive questionnaire on weight cutting and its associated protocols and symptoms prior to highest-level continental championships. Competition results were obtained at follow-up using a dichotomous variable: medal winning vs nonwinning at the European Championships.Results:Binary logistic regression analysis indicated that “boxing experience” was significantly related to the criterion competitive outcome (odds ratio = 1.33; 95% confidence interval, 1.06–1.66; NagelkerkeR² = .11), with a higher likelihood of competitive success for more-experienced boxers. Of all the youth boxers, only 25% were included in the RWL group, irrespective of their weight-class stratification. More than 45% of all the youth boxers self-reported the simultaneous combination of different weight-cutting methods that are known to be serious health hazards. Finally, 33% of the boxers experienced muscle weakness as a consequence of RWL.Conclusions:Our study provided evidence of pathogenic weight-management protocols that are widely adopted by youth boxers, and yet the present outcomes showed that RWL did not translate into competitive success in these elite Olympic-style boxers in Europe. Therefore, the authors suggest a mandatory educational program that should simultaneously target all the mentioned issues including both health- and performance-threatening consequences.

The present study investigated the effect of a 3% rapid weight loss (RWL) procedure on neuromuscular performance in elite, Olympic‐style boxers. Nine boxers were randomly assigned to two experimental procedures (RWL and control, in a randomized counter‐balance order) to perform 5‐s maximum isometric voluntary contractions (MVC) of the dominant leg knee extensors prior to (MVC1), and following (MVC2), a sustained, isometric contraction at 70% MVC until exhaustion. The voluntary activation (VA) was determined using percutaneous muscle stimulation and interpolated twitch technique. High (at 80 Hz) and low (at 20 Hz) frequency tetanic impulses were also delivered before and after the sustained 70% MVC to assess peripheral fatigue. Hydration status, hemodynamic parameters, and lactate concentration were assessed throughout the study. Body‐mass was reduced by ∼3% (during RWL) compared to control (p = .001). As a result of the RWL protocol, MVC1 force output was 12% lower and VA deficits of 7% were observed after the fatigue protocol compared to control (p = .001). Following RWL, time to exhaustion for the sustained 70% MVC was 69 ± 20 s compared to 86 ± 34 s for control (p = .020). Peak lactate production was 53% lower in RWL compared to control (p = .001). In conclusion, the 3% RWL procedure translated into significant decline in neuromuscular performance for both brief and sustained contractions in competitive boxers.

The microclimate of an airline cabin consists of dry, recirculated, and cool air, which is maintained at lower pressure than that found at sea level. Being exposed to this distinctive, encapsulated environment for prolonged durations, together with the short-term chair-rest immobilization that occurs during long-haul flights, can trigger distinct and detrimental reactions to the human body. There is evidence that long-haul flights promote fluid shifts to the lower extremity and induce changes in blood viscosity which may accelerate dehydration, possibly compromising an athlete’s potential for success upon arrival at their destination. Surprisingly, and despite several recent systematic reviews investigating the effects of jet lag and transmeridian travel on human physiology, there has been no systematic effort to address to what extent hypohydration is a (health, performance) risk to travelers embarking on long journeys. This narrative review summarizes the rationale and evidence for why the combination of fluid balance and long-haul flight remains a critically overlooked issue for traveling persons, be it for health, leisure, business, or in a sporting context. Upon review, there are few studies which have been conducted on actual traveling athletes, and those that have provide no real evidence of how the incidence rate, magnitude, or duration of acute dehydration may affect the general health or performance of elite athletes.