Modulation of EMG Parameters During Ankle Plantarflexor Fatigue in Trained Gymnasts and Healthy Untrained Controls

This study aimed to compare the modulation of time and frequency-domain EMG parameters between trained gymnasts and healthy untrained controls during a protocol designed to induce muscle fatigue on the ankle plantarflexor muscles. We hypothesized that neuromuscular adaptation due to training would lead to different behavior of EMG quantifiers along the fatiguing process. Twenty eight female volunteers (aged 11 to 26 years) were recruited and two groups were formed: acrobatic gymnastics athletes (GYN, n = 14) and non-gymnasts (control (CTRL), n = 14). Fatigue of the ankle plantarflexors (dominant leg) was induced by a sustained posture (standing on the toes) until exhaustion. Surface EMG signals were acquired from the tibialis anterior (TA), soleus (SO), lateral gastrocnemius (GL), medial gastrocnemius (GM), vastus lateralis (VL), biceps femoris (BF), spinal erector (EE) and rectus abdominis (RA) muscles. EMG amplitude (aEMG) and median frequency (Fmed) were computed in 3 different periods of the fatigue protocol: (1) during the initial 10 s, (2) during the central 10 s, and (3) during the last 10 s (final period). The results showed significant increases in aEMG values and significant decreases in Fmed values throughout the fatigue protocol, for almost all muscles investigated, indicating a fatigue effect that was not restricted to the target muscles (plantarflexors). Differences in muscle activation patterns (in both time and frequency-domain parameters) indicated that acrobatic gymnastics athletes, as compared to healthy untrained participants, used different neuromuscular control strategies during the sustained fatiguing isometric contraction.