Effect Of Blood Flow Occlusion On Changes In Torque Complexity During Intermittent Maximal-effort Contractions

Torque complexity reflects the modulation of motor output to active skeletal muscle. The development of neuromuscular fatigue results in a loss of torque complexity. Blood flow occlusion expedites neuromuscular fatigue development during intermittent maximal effort contractions (IMECs); however, the impact of occlusion on muscle torque complexity is unknown. PURPOSE: To test the hypothesis that blood flow occlusion would exacerbate the loss of torque complexity during IMECs performed until an end-test plateau in torque. METHODS: Sixteen participants (8 M/8F; 21 ± 2 yrs.) performed IMECs (forearm flexion) for 5-min under control conditions (CON) and with complete limb blood flow occlusion (OCC) followed by immediate reperfusion (REP). OCC was initiated at the start of the test and persisted until maximal-effort torque was <15% of baseline maximal torque production. REP was initiated immediately following OCC and IMECs were performed without interruption until the end of the 5-min test. For all contractions, torque variability was characterized by the coefficient of variation (CV) and torque complexity was characterized by fuzzy entropy (FEn) and detrended fluctuation analysis (DFAα). Data from three consecutive contractions were averaged at Start, End-OCC (and time-matched CON), and End-Test. Comparisons were made using two-way repeated measures ANOVAs (condition × time). RESULTS: Mean torque progressively decreased during CON until the end-test plateau (p < 0.001). Mean torque was lower at End-OCC compared to CON (89 ± 36 vs 190 ± 76, p < 0.001) but not different at End-test between CON and REP (163 ± 62 vs. 157 ± 53, p > 0.05). CV progressively increased during CON (p < 0.001). On average, CV was higher at End-OCC compared to CON but was not significant (p > 0.05). CV was not different at End-test between CON and REP (p > 0.05). There were no effects of time or condition on DFAα (p > 0.05). FEn was significantly lower at End-OCC compared to CON (0.11 ± 0.02 vs. 0.13 ± 0.03, p < 0.01), and returned to similar values by End-test after REP (0.13 ± 0.03 vs. 0.13 ± 0.04, p > 0.05). CONCLUSION: The fall in FEn reflects an exacerbated loss in torque complexity with limb blood flow occlusion. Considering the return of complexity during REP, these data suggest oxygen availability acutely impacts motor unit control during IMECs.