Faculty of Physical Activity and Sports, Flores University, Buenos Aires, Argentina.
Faculty of Sports Sciences, University Pablo de Olavide, Seville, Spain.
J Strength Cond Res. 2022 Jul 1;36(7):1839-1846. doi: 10.1519/JSC.0000000000003723. Epub 2020 Jul 9.
Zabaloy, S, Carlos-Vivas, J, Freitas, TT, Pareja-Blanco, F, Loturco, I, Comyns, T, Gálvez-González, J, and Alcaraz, PE. Muscle activity, leg stiffness and kinematics during unresisted and resisted sprinting conditions. J Strength Cond Res 36(7): 1839-1846, 2022-This study aimed to compare muscle activity, leg stiffness, and kinematics (contact and flight time [FT], stride length and frequency, and trunk angle [TA]) of unloaded sprinting to resisted sprint (RST) using different loads. Twelve male rugby players (age: 23.5 ± 5.1 years; height: 1.79 ± 0.04 m; body mass 82.5 ± 13.1 kg) performed 30-m sprints using different loading conditions (0, 10, 30 and 50% of velocity loss-Vloss-from the maximum velocity reached under unloaded condition). Muscle activity from 4 muscles (biceps femoris long head, rectus femoris [RF], gluteus medius and gastrocnemius), leg stiffness (Kleg), and kinematics were measured during the acceleration and maximum velocity (Vmax) phases of each sprint. Heavier loads led to significantly lower biceps femoris long head activation and higher rectus femoris activity (p < 0.01-0.05). Significant reductions in Kleg were observed as loading increased (p < 0.001-0.05). Kinematic variables showed substantial changes with higher loads during the acceleration and Vmax phase. In conclusion, the heavier the sled load, the higher the disruptions in muscle activity, Kleg, and kinematics. When coaches and practitioners intend to conduct resisted sprint training sessions without provoking great disruptions in sprint technique, very-heavy sled loads (greater than 30% Vloss) should be avoided. However, heavy sled loads may allow athletes to keep specific positions of the early acceleration phase for longer time intervals (i.e., first 2-3 strides during unresisted sprints).
扎巴洛，S，卡洛斯-维瓦斯，J，弗雷塔斯，TT，帕雷哈-布兰科，F，洛特库罗，I，科明斯，T，加尔韦斯-冈萨雷斯，J，和阿尔卡拉兹，PE。无阻力和阻力冲刺条件下的肌肉活动、腿部刚度和运动学。J 力量与条件研究 36(7)：1839-1846，2022 年-本研究旨在比较无负载冲刺和阻力冲刺（RST）的肌肉活动、腿部刚度和运动学（接触和飞行时间[FT]、步长和频率以及躯干角度[TA]），使用不同的负载。12 名男性橄榄球运动员（年龄：23.5±5.1 岁；身高：1.79±0.04 m；体重 82.5±13.1 kg）使用不同的加载条件（0、10、30 和 50%的速度损失-Vloss-从无负载条件下达到的最大速度）进行 30-m 冲刺。在每个冲刺的加速和最大速度（Vmax）阶段测量 4 块肌肉（股二头肌长头、股直肌[RF]、臀中肌和腓肠肌）、腿部刚度（Kleg）和运动学的肌肉活动。随着负载的增加，股二头肌长头的激活显著降低，股直肌的活性显著增加（p<0.01-0.05）。随着负载的增加，腿部刚度（Kleg）显著降低（p<0.001-0.05）。随着负载的增加，在加速和 Vmax 阶段，运动学变量发生了很大的变化。结论是，雪橇负载越重，肌肉活动、腿部刚度和运动学的干扰就越大。当教练和从业者打算进行无阻力冲刺训练而不引起冲刺技术的巨大干扰时，应避免非常重的雪橇负载（大于 30%的 Vloss）。然而，重雪橇负载可以使运动员在更长的时间间隔内保持早期加速阶段的特定位置（即无阻力冲刺的前 2-3 步）。
