Neuromuscular fatigue induced by an isotonic heavy-resistance loading protocol in knee extensors

Abstract

The main aim of this study was to assess neuromuscular fatigue during a typical high-load, low-repetition loading protocol. Muscle stimulations were used to assess maximum voluntary contraction, resting single- and double-pulse twitch characteristics, and superimposed double-pulse twitch force (used to calculate voluntary activation) before and after an acute knee extension loading protocol. In our participants, who had previous resistance training experience, the mean voluntary activation level was 96.2% in an unfatigued state. Maximum voluntary contraction (?11.8%), resting double-pulse twitch force (?10.6%), and voluntary activation (?2.1%) were markedly decreased as a consequence of loading (P < 0.05). In addition, although potentiated twitch characteristics were observed during the loading protocol, this was short-lived, as fatigue surpassed the potentiation mechanisms. Our results show that both central and peripheral mechanisms contributed to neuromuscular fatigue during the present loading protocol.     

The effect of a familiarisation period on subsequent strength gain

Abstract

Untrained subjects can display diverse strength gain following an identical period of resistance exercise. In this investigation, 28 untrained males completed 16-weeks of resistance exercise, comprising 4-weeks familiarisation, and 12-weeks of heavy-load (80–85%) activity. High and low responders were identified by the Δ1RM (Δ one repetition maximum) observed following familiarisation (25.1 ± 1.4%, 9.5 ± 1.4%, P < 0.0001) and differences in electromyographic root mean square amplitude (ΔEMG_RMS 29.5 ± 8.3%, 2.4 ± 6.0%, P = 0.0140), and habitual and occupational activity patterns were observed between these respective groups. The strength gain (P < 0.0001) observed within high (29.6 ± 1.7%) and low (31.4 ± 2.7%) responding groups was similar during the heavy-load phase, yet ΔEMG_RMS increased (P = 0.0048) only in low responders (31.5 ± 9.3%). Retrospectively, differences (P < 0.0001) in baseline 1RM strength of high- (19.7 ± 0.9 kg) and low-responding (15.6 ± 0.7 kg) groups were identified, and a strong negative correlation with Δ1RM after 16-weeks (r ² = ?0.85) was observed. As such, baseline 1RM strength provided a strong predicative measure of strength adaptation. The ΔEMG_RMS suggests strength variability within high and low responders may be attributed to neural adaptation. However, differences in habitual endurance and occupational physical activity suggests one should consider screening not only recent resistance training, but also other modes of physical activity during participant recruitment.     

Do kinaesthetic tapes affect plantarflexor muscle performance?

Abstract

This study aimed to examine the effects of application of kinaesthetic tapes on plantarflexor muscle performance. We hypothesised that taping of the triceps surae muscle would improve plantarflexor muscle strength and endurance with no significant effect on drop jump performance. Using a repeated-measures design, all performance measures were obtained in 24 volunteers on two separate occasions: without tapes and after application of kinaesthetic tapes. Performance tests included measurements of isometric plantarflexor muscle strength and the associated electromyographic activity of the gastrocnemius muscle, an isokinetic fatigue resistance test (30 contractions at 180° · s^?1) and assessments of drop jump performance. The taping-intervention was associated with an increase in gastrocnemius electromyographic activity. However, significant increases in isometric strength were only found at fully dorsiflexed ankle positions (+12% at ?20°). Strength gains were negatively correlated to baseline strength (r = ?.58). The intervention did not affect the results of the isokinetic fatigue and drop jump tests. The application of kinaesthetic tapes over the triceps surae muscle promotes an increase in isometric strength and gastrocnemius muscle activity. Our data suggest that these effects are joint-angle dependent and more prominent in weaker individuals. By contrast, the taping-intervention improves neither drop jump performance nor muscular endurance.     

Evaluation of aerodynamic and rolling resistances in mountain-bike field conditions

Abstract

Aerodynamic and rolling resistances are the two major resistances that affect road cyclists on level ground. Because of reduced speeds and markedly different tyre-ground interactions, rolling resistance could be more influential in mountain biking than road cycling. The aims of this study were to quantify 1) aerodynamic resistance of mountain-bike cyclists in the seated position and 2) rolling resistances of two types of mountain-bike tyre (smooth and knobby) in three field surfaces (road, sand and grass) with two pressure inflations (200 and 400 kPa). Mountain-bike cyclists have an effective frontal area (product of projected frontal area and drag coefficient) of 0.357 ± 0.023 m², with the mean aerodynamic resistance representing 8–35% of the total resistance to cyclists' motion depending on the magnitude of the rolling resistance. The smooth tyre had 21 ± 15% less rolling resistance than the knobby tyre. Field surface and inflation pressure also affected rolling resistance. These results indicate that aerodynamic resistance influences mountain-biking performance, even with lower speeds than road cycling. Rolling resistance is increased in mountain biking by factors such as tyre type, surface condition and inflation pressure that may also alter performance.     

Reliability of force-velocity parameters obtained from linear and curvilinear regressions for the bench press and squat exercises

ABSTRACT

This study aimed to compare the goodness of fit and the reliability of different regression models for fitting the force-velocity relationship (FV) of bench press (BP) and squat (SQ). Additionally, the reliability of the position on FV of the velocity (V_1RM) and the force performed with the 1RM (F_1RM) was explored. Nine rugby players and 12 judokas participated in this study. The FV of BP and SQ were obtained twice by a protocol performed until the 1RM. Individual FV were fitted by linear (LM), quadratic polynomial (PM), and exponential models (EM). Adjusted coefficients of determination of LM and PM (medians higher than 0.919) were higher than for EM. The reliability was higher for LM in comparison with PM. The reliability of V_1RM was not acceptable (CV% = 19 and 18% for BP and SQ). High reliability was observed for F_1RM (CV% = 3 and 2% for BP and SQ) and for the ratio between F_1RM and the force-axis intercept of FV (CV% = 2 and 4% for BP and SQ). The reliability of the relative values of F_1RM around 92 and 87% of F₀ for BP and SQ suggests the use of these values for monitoring resistance training programmes.     

The acute effects of resistance exercise on affect,anxiety, and mood – practical implications for designing resistance training programs

ABSTRACT

Research in aerobic exercise has linked the affective responses (pleasure–displeasure) experienced during exercise to future exercise participation. While this is yet to be confirmed in anaerobic activities, it can be inferred that making resistance exercise (RE) more psychologically rewarding is an important consideration. The purpose of this article is to review the acute effects of RE on affect, anxiety, and mood and to draw conclusions on how to maximize feelings of pleasure in an effort to increase rates of participation. This review provides evidence to support lower training volumes performed at low to moderate intensities (50–70% 1RM) with long inter-set rest intervals (90–150 s). Additional recommendations are provided based on physiological and theoretical support, but there is a strong need for more research on the affective experience of RE.     

浅谈饮料在体育运动中抗疲劳功效价值研究

采用文献资料法等分析饮料在体育运动中抗疲劳功效及价值。主要结论:功能性饮料能够短时高效的补充能量和抗疲劳,滥用会引起心血管系统异常。茶饮可通过胶原蛋白合成加速运动损伤中组织创口愈合,茶饮中咖啡碱可引起中枢神经兴奋、增大肌肉张力、消除疲劳。鲜榨果蔬饮料能及时补充运动后人体所需各种微量元素,促进胃肠道蠕动,具有改善疲劳抗氧化等功效。矿物质饮料提供运动时人体所需矿物质元素,改善运动时人体内环境平衡,具有镇痛抗氧化、提高免疫力及增强身体素质,消除疲劳等作用。运动后饮用碳酸饮料会引发腹胀,易于出现注意力不集中、心悸、疲乏等困意感,存在引发骨质酥松症,增加运动中骨折的风险。含有乳清蛋白的乳饮料有助于提高机体能量,帮助重建受损的肌纤维,可延缓中枢神经系统疲劳,更好地提升运动耐力和运动表现。     

Overreaching and overtraining in strength sports and resistance training: A scoping review

ABSTRACT

To date, little is known about overreaching (OR) and the overtraining syndrome (OTS) in strength sports and resistance training (RT) populations. However, the available literature may elucidate the occurrence of both conditions in these populations. A scoping review was conducted. SPORTDiscus, Scopus and Web of Science were searched in a robust and systematic manner, with relevant articles analysed. 1170 records were retrieved during an initial search, with a total of 47 included in the review. Two broad themes were identified during data extraction: 1) overreaching in strength sports; 2) overreaching and overtraining syndrome in RT. Short-term periods of OR achieved with either high-volume or high-intensity RT can elicit functional OR (FOR) but there is also evidence that chronic high-volume and/or intensity RT can lead to non-functional overreaching (NFOR). There is minimal evidence to suggest that true OTS has occurred in strength sports or RT based on the studies entered during this review. More research is needed to develop robust guiding principles for practitioners. Additionally, due to the heterogeneous nature of the existing literature, future research would benefit from the development of practical tools to identify and diagnose the transition from FOR to NFOR, and subsequently OTS in strength athletes and RT populations.     

运动与骨骼肌葡萄糖转运通路研究进展

经过近40年的研究,现在已经证实不论是规律的有氧运动、剧烈的单次运动或者长期的抗阻训练,以及有氧结合抗阻运动训练都可以缓解胰岛素抵抗症状、增强胰岛素敏感性、提高整个机体的血糖清除能力以及增加骨骼肌的葡萄糖转运能力。在骨骼肌胰岛素信号转导通路涉及:胰岛素受体自动磷酸化、IRS-1/2酪氨酸残基的磷酸化、酪氨酸激酶激活以及磷脂酰肌醇3激酶的激活。而运动诱导的骨骼肌葡萄糖转运能力提高涉及的机制尚未明确。目前的研究主要集中在AMPK、CaMK、MAPKs、PKCs以及SIRTs等信号分子。在此对近年来关于AMPK和CaMK在运动诱导骨骼肌葡萄糖转运中的作用的研究进展进行综述。     

浅谈混凝土温度裂缝的控制和预防

混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题。在工程中对混凝土温度应力变化引起的裂缝很容易被忽视。通过对混凝土工程中的温度裂缝问题进行探讨分析,提出了一些预防和处理措施。