To determine the effect of very high stimulation frequency (150 and 200 Hz) with wide pulse duration versus 50 Hz with wide pulse duration on stimulated force and fatigue of quadriceps femoris in healthy participants.
Thirty-four healthy participants underwent fatigue test using three stimulation frequency conditions (50, 150, and 200 Hz) with pulse duration of 0.9 ms. Normalized force values at the end of each fatigue protocol and curve fitting patterns were compared among stimulated frequencies.
Very high stimulation frequency (150 and 200 Hz) conditions showed a trend of having more decline in normalized stimulated force during fatigue test compared to a low stimulation frequency at 50 Hz. However, the difference was not statistically significant. Responder group showed the same slope of a linear fitting pattern, implying the same pattern of muscle fatigue among three stimulation frequency conditions (−3.32 in 50 Hz, −2.88 in 150 Hz, and −3.14 in 200 Hz, respectively).
There were high inter-subject variations in the response to different frequency stimulation conditions. However, very high stimulation frequency generated the same fatigue pattern as the low stimulation frequency in the responder group. Further research is needed to explore the mechanism involved.
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To investigate associations between angiotensin-converting enzyme (ACE) polymorphisms and muscle fatigability in 65-year-old Koreans.
The study participants were 49 Koreans aged 65 years. ACE insertion/deletion (I/D) polymorphisms were determined by polymerase chain reaction and serum ACE activity, by spectrophotometry. Body mass index (BMI), body fat mass (BFM), and lean body mass (LBM) were determined. To evaluate muscle fatigability, dynamic Electromyography was used to measure maximum voluntary isometric contractions (MVICs) of ankle plantar flexor muscles. Patients were seated with their hips flexed at 90°, knees fully extended, and ankles at 0°. Continuous submaximal VICs (40% MVIC) were then performed, and contraction duration and EMG frequency changes during the initial 2 min were measured. A self-reported physical activity questionnaire was used to evaluate effects of ACE activity levels on muscle fatigability.
Among the 49 volunteers, 15 showed II genotype; 22, ID genotype; and 12, DD genotype. Serum ACE activity levels were significantly higher in DD genotype subjects than in II genotype subjects (p<0.05). Furthermore, the duration of submaximal isometric contractions was longer in II and ID genotype subjects than in DD genotype subjects (p<0.05). Dynamic EMG showed significantly lower mean frequency changes in II genotype subjects than in DD genotype subjects (p<0.05). However, LBM, BFM, and BMI were independent of ACE genotypes.
ACE II genotype subjects showed significantly higher resistant to muscle fatigue than that by DD genotype subjects. However, body composition and BMI showed no correlations with ACE I/D polymorphisms.
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Objective: To determine whether muscle fatigue affects knee joint proprioception.
Method: Thirty healthy subjects (18 male and 12 female) with an average age of 22.1 years were selected for this study. Angular errors were measured to test propriocetive function in the knee joint. In a sitting position, the subject's dominant leg was passively positioned to the 45o knee flexion stimulus point for 2∼4 second, while the subject concentrated on this position, the leg was passively returned to the 90o flexion position, afterward the subject was asked to duplicate the stimulus point actively. The difference, in degrees between the stimulus point and the reproduced point is an angular error. All subjects were blindfolded and underwent proprioception measurement before and after the muscle fatigue. Isokinetic exercises performed at 180 degree/sec on the Cybex Orthotron II(Cybex, a division of Lumex, Inc. USA) were used to induce the muscle fatigue. All subjects performed an isokinetic exercise with their dominant leg. Exercise was continued until 50% of the initial peak torque was reached. When the subjects were fatigued to less than 50% of the initial peak torque, the isokinetic exercises were discontinued. Then we immediately retested the proprioception using the same method.
Results: The mean and standard deviation of the angular error increased from 2.79⁑1.17o to 6.40⁑3.42o after muscle fatigue.
Conclusion: The proprioception significantly decreased after the muscle fatigue(p＜0.001). This result suggests that the muscle fatigue must be considered when an injured professional athlete a patient with fatigable disease is set in a rehabilitation program. Further studies are required to determine the physiological mechanisms of the role of muscle fatigue for the decreasing proprioception.
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