TY - JOUR
T1 - Changes in motor unit behaviour across repeated bouts of eccentric exercise
AU - Hayman, Oliver
AU - Ansdell, Paul
AU - Angius, Luca
AU - Thomas, Kevin
AU - Horsbrough, Lauren
AU - Howatson, Glyn
AU - Kidgell, Dawson J.
AU - Škarabot, Jakob
AU - Goodall, Stuart
PY - 2024/11/1
Y1 - 2024/11/1
N2 - Unaccustomed eccentric exercise (EE) is protective against muscle damage following a subsequent bout of similar exercise. One hypothesis suggests the existence of an alteration in motor unit (MU) behaviour during the second bout, which might contribute to the adaptive response. Accordingly, the present study investigated MU changes during repeated bouts of EE. During two bouts of exercise where maximal lengthening dorsiflexion (10 repetitions × 10 sets) was performed 3 weeks apart, maximal voluntary isometric torque (MVIC) and MU behaviour (quantified using high‐density electromyography; HDsEMG) were measured at baseline, during (after set 5), and post‐EE. The HDsEMG signals were decomposed into individual MU discharge timings, and a subset were tracked across each time point. MVIC was reduced similarly in both bouts post‐EE (Δ27 vs. 23%, P = 0.144), with a comparable amount of total work performed (∼1,300 J; P = 0.905). In total, 1,754 MUs were identified and the decline in MVIC was accompanied by a stepwise increase in discharge rate (∼13%; P < 0.001). A decrease in relative recruitment was found immediately after EE in Bout 1 versus baseline (∼16%; P < 0.01), along with reductions in derecruitment thresholds immediately after EE in Bout 2. The coefficient of variation of inter‐spike intervals was lower in Bout 2 (∼15%; P < 0.001). Our data provide new information regarding a change in MU behaviour during the performance of a repeated bout of EE. Importantly, such changes in MU behaviour might contribute, at least in part, to the repeated bout phenomenon.
AB - Unaccustomed eccentric exercise (EE) is protective against muscle damage following a subsequent bout of similar exercise. One hypothesis suggests the existence of an alteration in motor unit (MU) behaviour during the second bout, which might contribute to the adaptive response. Accordingly, the present study investigated MU changes during repeated bouts of EE. During two bouts of exercise where maximal lengthening dorsiflexion (10 repetitions × 10 sets) was performed 3 weeks apart, maximal voluntary isometric torque (MVIC) and MU behaviour (quantified using high‐density electromyography; HDsEMG) were measured at baseline, during (after set 5), and post‐EE. The HDsEMG signals were decomposed into individual MU discharge timings, and a subset were tracked across each time point. MVIC was reduced similarly in both bouts post‐EE (Δ27 vs. 23%, P = 0.144), with a comparable amount of total work performed (∼1,300 J; P = 0.905). In total, 1,754 MUs were identified and the decline in MVIC was accompanied by a stepwise increase in discharge rate (∼13%; P < 0.001). A decrease in relative recruitment was found immediately after EE in Bout 1 versus baseline (∼16%; P < 0.01), along with reductions in derecruitment thresholds immediately after EE in Bout 2. The coefficient of variation of inter‐spike intervals was lower in Bout 2 (∼15%; P < 0.001). Our data provide new information regarding a change in MU behaviour during the performance of a repeated bout of EE. Importantly, such changes in MU behaviour might contribute, at least in part, to the repeated bout phenomenon.
KW - fatigue
KW - high-density electromyography
KW - motoneuron
KW - muscle damage
KW - recovery
UR - http://www.scopus.com/inward/record.url?scp=85203008751&partnerID=8YFLogxK
U2 - 10.1113/ep092070
DO - 10.1113/ep092070
M3 - Article
C2 - 39226215
SN - 0958-0670
VL - 109
SP - 1896
EP - 1908
JO - Experimental Physiology
JF - Experimental Physiology
IS - 11
ER -