Ratkevicius A, Skurvydas A, Povilonis E, Quistorff B, Lexell J
Department of Physiology and Biochemistry, Lithuanian Institute of Physical Education, Kaunas.
Eur J Appl Physiol Occup Physiol. 1998 Apr;77(5):462-8. doi: 10.1007/s004210050361.
The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise.
本研究的目的是调查低频疲劳（LFF）是否取决于重复肌肉收缩的持续时间，并比较自愿运动和电刺激运动中的低频疲劳。男性受试者分别按照方案1、2和3进行了3个9分钟的重复等长伸膝运动，运动强度为最大自主收缩的40%，收缩加放松时间分别为30加60秒、15加30秒和5加10秒。使用反馈控制的电刺激以最大强直扭矩的40%重复相同的运动方案。在每个运动周期之前和之后15分钟，评估1、7、10、15、20、50和100赫兹时的伸膝扭矩。在自愿运动期间，评估股外侧肌的肌电图均方根（EMGrms）。与自愿运动后相比，电刺激运动后20赫兹扭矩与100赫兹扭矩（20:100赫兹扭矩）的比值降低得更多（P<0.05）。在电刺激运动期间，随着单次收缩时间缩短，20:100赫兹扭矩比值的下降逐渐减少（P<0.05）。在自愿运动期间，方案1中20:100赫兹扭矩比值的下降和EMGrms的增加大于方案2和3（P<0.01），而方案2和3之间没有差异。总之，我们的结果表明，在重复性等长运动中，低频疲劳取决于单个肌肉收缩的持续时间，并且与次最大强度的自愿运动相比，电刺激运动产生的低频疲劳更明显。有人认为，在自愿运动期间，更快收缩运动单位的代偿性募集是影响低频疲劳严重程度的另一个因素。
