Sex differences in muscle fatigue following isokinetic muscle contractions

Muscle fatigue is a limiting factor of human performance. It is unclear whether sex-based differences in fatigability exist during dynamic exercise of varying velocities of contraction. We aimed at exploring sex differences in muscle fatigue elicited by maximal isokinetic muscle contractions performed at different angular velocities. Twenty-six healthy participants (13 men: 23.2 ± 1.5; 13 women: 21.9 ± 3.0 years) were tested for concentric knee-extension at slow, moderate and fast angular isokinetic velocity (60, 180 and 300º.s−1, respectively), on non-consecutive days. The impact of sex on fatigue resistance and consecutive recovery for each isokinetic condition was explored by calculating the percent change in maximal voluntary isometric contraction (MVIC) and in rate of torque development (RTD), from pre- to post-isokinetic exercise (30 repetitions). The isokinetic fatigue index was also determined. No sex differences were obtained in response to isokinetic contractions completed at 60º.s−1. After performing muscle contractions at 300º.s−1, women had a significantly greater loss in MVIC than men (− 18.4 ± 5.5 vs. − 12.9 ± 3.8%; p = 0.009) and larger decreases in work output during isokinetic exercise (− 34.2 ± 8.9 vs − 27.5 ± 10.6%; p = 0.017). Recovery of initial MVIC strength was greater for women post-exercise at 180º.s−1 (15.6 ± 4.1% vs. 6.7 ± 9.5; p = 0.003). No differences were found between sexes in any condition for RTD from pre- to post-fatigue. These results suggest the presence of a sexually dimorphic fatigability in response to dynamic (isokinetic) contractions favouring men at higher absolute velocities of contraction.

Sex Differences in Muscle Fatigue Following Isokinetic Muscle Contractions

Muscle fatigue is a limiting factor of human performance. It is unclear whether sex-based differences in fatigability exist during dynamic exercise of varying velocities of contraction. We aimed at exploring sex differences in muscle fatigue elicited by maximal isokinetic muscle contractions performed at different angular velocities. Twenty-six healthy participants (13 men: 23.2 ± 1.5; 13 women: 21.9 ± 3.0 years) were tested for knee-extension at slow, moderate and fast angular velocity (60, 180 and 300º.s-1, respectively). The impact of sex on fatigue resistance and consecutive recovery for each isokinetic condition was explored by calculating the percent change in maximal voluntary isometric contraction (MVIC) and in rate of torque development (RTD), from pre- to post-isokinetic exercise. The isokinetic fatigue index was also determined. No sex differences were obtained in response to isokinetic contractions completed at 60º.s-1. After performing muscle contractions at 300º.s-1, women had a significantly greater loss in MVIC than men (-18.4 ± 5.5 vs. -12.9 ± 3.8%; p = 0.009) and larger decreases in work output during isokinetic exercise (-34.2 ± 8.9 vs -27.5 ± 10.6 %; p = 0.017). Recovery of initial MVIC strength was greater for women post-exercise at 180º.s-1 (6.7 ± 9.5 vs. 15.6 ± 4.1%; p = 0.003). No differences were found between sexes in any condition for RTD from pre- to post- fatigue. These results suggest the presence of a sexually dimorphic fatigability in response to dynamic (isokinetic) contractions favouring men at higher velocities of contraction.

Evaluation of the Electromyographic Amplitude-to-Work Ratio in the Infraspinatus Muscle During External Shoulder Rotation Exercises: A Comparison of Concentric Isotonic and Isokinetic Exercises

Background: Isotonic exercise is commonly adopted for shoulder rehabilitation, but the efficacy of isokinetic exercise for rehabilitation has not been evaluated. Purpose: To evaluate the efficacy of isotonic and isokinetic external shoulder rotation exercises. Study Design: Controlled laboratory study. Methods: Using surface electromyography (EMG) and the Biodex system, we investigated the EMG amplitude of the infraspinatus (IS), total work (tWK), and EMG(IS)/tWK ratio and examined the relative IS and posterior deltoid (PD) contributions to all exercises. A total of 24 healthy participants without musculoskeletal injuries were included. Participants performed isotonic external shoulder rotation at 10%, 20%, 30%, 40%, and 50% of the maximum voluntary isometric contraction (MVIC) as well as isokinetic external shoulder rotation at angular velocities of 60, 120, 180, 240, and 300 deg/s. Levels of intensity were classified from 1 to 5: level 1 corresponded to 10% of the MVIC and a 300-deg/s angular velocity; level 2 corresponded to 20% MVIC and 240 deg/s; level 3 corresponded to 30% MVIC and 180 deg/s; level 4 corresponded to 40% MVIC and 120 deg/s; and level 5 corresponded to 50% MVIC and 60 deg/s. Normalized IS and tWK amplitudes were calculated for each exercise. Results: During isotonic exercise, the EMG(IS)/tWK ratio significantly decreased from level 5 to 3, 2, and 1; from level 4 to 2 and 1; and from level 3 to 1. During isokinetic exercise, the EMG(IS)/tWK ratio at level 3 was greater than that at all other levels except level 1. Statistical differences were found between isotonic and isokinetic modes at levels 1, 2, and 3. The IS/PD activation ratios were not significantly different between exercise modes at any level. Conclusion: Isokinetic resistance may provide more effective stimulation of the IS muscle compared with isotonic resistance. Clinical Relevance: Isokinetic exercise needs to be considered as a method of rehabilitation that effectively increases infraspinatus muscle activity.

CARDIORESPIRATORY RESPONSES TO ISOKINETIC EXERCISE IN PATIENTS WITH CORONARY ARTERY DISEASE

ABSTRACT Introduction Exercise training using an isokinetic dynamometer is an alternative for improving muscle strength in patients with coronary artery disease (CAD). Few studies have shown metabolic and cardiorespiratory responses to submaximal isokinetic exercises in patients in cardiac rehabilitation programs. Objective To describe cardiorespiratory responses at two intensities of isokinetic exercise. Additionally, we compared the cardiorespiratory responses of isokinetic exercise with data from the incremental cardiopulmonary exercise test (CPET). Methods Eight individuals with CAD (61.7 ± 6.6 years) performed the following tests: 1) CPET on a treadmill; 2) Peak torque test (five repetitions) and fatigue resistance test (20 repetitions) of knee flexion-extension at angular speeds of 120°/s and 180°/s; 3) Two sets of 20 repetitions were performed at 30–40% (low-intensity, LI) and 50–60% (moderate-intensity, MI) of peak torque at angular speeds of 120°/s and 180°/s, using an isokinetic dynamometer. During the exercises, the individuals were connected to an expired gases analyzer with simultaneous monitoring of the electrocardiogram trace, heart rate (HR), oxygen consumption (VO2), carbon dioxide production, and minute ventilation (VE). The differences (∆) between the peak measurements during exercises and the baseline values were calculated. Results Both LI and MI produced cardiorespiratory responses below the anaerobic threshold (82.8 ± 8.1% of HRmax and 74.4 ± 9.6% of VO2peak) compared to the CPET data ( P < 0.01). MI showed higher ∆ HR (9.8 ± 5.5 vs. 6.3 ± 4.6 bpm; P = 0.01), ∆ rate pressure product (3015 ± 2286 vs. 1957 ± 1932 mmHg·bpm; P = 0.01), and ∆VE (10.2 ± 6.2 vs. 6.9 ± 7 L·min-1; P = 0.03) than LI at the angular velocity of 180°/s. Conclusion These results suggest that this isokinetic exercise protocol may be used as a strategy for cardiac rehabilitation programs in patients with CAD. Level of evidence IV; Case series.