期刊
EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY
卷 121, 期 11, 页码 3117-3131出版社
SPRINGER
DOI: 10.1007/s00421-021-04779-1
关键词
Exercise; Oxygen consumption; Non-linear dynamics; Complexity endurance; Muscle fatigue
资金
- Leverhulme Trust [RPG-2016-440]
The study showed that the correlation between torque complexity and metabolic rate may change as joint angle decreases, and muscle length during high-intensity contractions has an impact on this correlation.
Purpose Joint angle is a significant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate (m<(V)over dot>O-2) would be conserved at reduced joint angles (i.e. shorter muscle lengths). Methods Eleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30 degrees, 60 degrees and 90 degrees of flexion (0 degrees = extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) alpha. m<(V)over dot>O-2 was determined using near-infrared spectroscopy. Results Time to task failure/end increased as joint angle decreased (P < 0.001). Over time, complexity decreased at 90 degrees and 60 degrees (decreased ApEn, increased DFA alpha, both P < 0.001), but not 30 degrees. m<(V)over dot>O-2 increased at all joint angles (P < 0.001), though the magnitude of this increase was lower at 30 degrees compared to 60 degrees and 90 degrees (both P < 0.01). There were significant correlations between torque complexity and m<(V)over dot>O-2 at 90 degrees (ApEn, r = - 0.60, P = 0.049) and 60 degrees (ApEn, r = - 0.64, P = 0.035; DFA alpha, rho = 0.68, P = 0.015). Conclusion The lack of correlation between m<(V)over dot>O-2 and complexity at 30 degrees was likely due to low relative task demands, given the similar kinetics of m<(V)over dot>O-2 and torque complexity. An inverse correlation between m<(V)over dot>O-2 and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths.
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