Immediate crossover fatigue after unilateral submaximal eccentric contractions of the knee flexors involves peripheral alterations and increased global perceived fatigue

Abstract

After a unilateral muscle exercise, the performance of the non-exercised contralateral limb muscle can be also impaired. This crossover fatigue phenomenon is still debated in the literature and very few studies have investigated the influence of eccentric contractions. This study was designed to assess neuromuscular adaptations involved in the crossover fatigue of the non-exercised contralateral knee flexor muscles. Seventeen healthy young men performed a unilateral submaximal eccentric exercise of the right knee flexors until a 20% reduction in maximal voluntary isometric contraction torque was attained in the exercised limb. Before (PRE), immediately after exercise cessation (POST) and 24 hours later (POST24), neuromuscular function and perceived muscle soreness were measured in both the exercised limb and non-exercised limb. In addition, global perceived fatigue was assessed at each measurement time. At POST, significant reductions in maximal voluntary isometric contraction were observed in the exercised limb (-28.1%, p < 0.001) and in the non-exercised limb (-8.5%, p < 0.05), evidencing crossover fatigue. At POST, voluntary activation decreased in the exercised limb only (-6.0%, p < 0.001), while electrically evoked potentiated doublet torque was impaired in both the exercised limb and the non-exercised limb (-11.6%, p = 0.001). In addition, global perceived fatigue significantly increased at POST (p < 0.001). At POST24, all measured variables returned to PRE values, except for perceived muscle soreness scores exhibiting greater values than PRE (p < 0.05). A possible cumulative interaction between peripheral alterations and global perceived fatigue may account for the immediate crossover fatigue observed in the non-exercised limb.

Fig 1. Overview of the experimental procedure.

After a familiarization session, a first session (Session 1) assessed the neuromuscular function of both the EL (exercised limb) and the NEL (non-exercised limb), as well as global perceived fatigue (RPF) and perceived muscle soreness (PMS), before (PRE) and immediately after (POST) a unilateral submaximal fatiguing eccentric exercise of the EL knee flexors. A second session (Session 2) performed 24 hours after the exercise (POST24) was similar to PRE testing. Maximal voluntary isometric contraction (MVIC), 1 Repetition Maximum eccentric contraction (1RM ECC).

Fig 2. Measures analyzed during the unilateral submaximal eccentric exercise.

Panel a: MVIC expressed as a percentage of the initial value (black line) and torque-time integral (dashed bars; mean ± standard error) of the exercised limb. Panel b: Surface electromyography of the biceps femoris muscle (BF RMS) expressed as a percentage of the initial value of both the EL (exercised limb; black bars) and the NEL (non-exercised limb; gray bars). ^$$$ MVIC significantly different from initial value at p < 0.001. ^£££ MVIC significantly different from initial, 25%, 50% and 75% values at p < 0.001. ^§ and ^§§ Torque-time integral produced during the third and the fourth quarter of exercise duration significantly different from the first quarter at p < 0.05 and p < 0.01, respectively. *** Pooled BF RMS values of the EL significantly different from the NEL at p < 0.001. MVIC Maximal voluntary isometric contraction.

Fig 3. Effects of the unilateral submaximal eccentric exercise on knee flexor’s of neuromuscular function and perceived muscle soreness (PMS) of both the EL (exercised limb) and the NEL (non-exercised limb) as well as global perceived fatigue (RPF).

Values in bold are statistically significant. *** Significantly different from PRE values at p < 0.001. ^$ PMS scores of both the EL and NEL significantly greater at POST24 compared to PRE at p < 0.05. PMS and RPF scores are presented as median (interquartile range). BF Biceps Femoris, BF RMS/M Root Mean Square values of BF muscle normalized to the respective BF compound muscle action potential.

Fig 4. Effects of the unilateral submaximal eccentric exercise on knee flexor’s neuromuscular function.

Panel a: MVIC (Maximal voluntary isometric contraction). Panel b: voluntary activation. Panel c: Dt_100Hz (Potentiated torque evoked at 100 Hz). Panel d: Dt_10Hz (Potentiated torque evoked at 10 Hz). Measures realized before (PRE; black bars), immediately after (POST; gray bars) and 24 (POST24; white bars) hours after the exercise in both the EL (exercised limb) and the NEL (non-exercised limb). * and *** indicate significant differences between PRE and POST at p < 0.05 and p < 0.001, respectively. ^$$$ pooled values of both the EL and the NEL measured at POST significantly different from pooled EL and NEL values measured at PRE at p < 0.001.