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Fatigability and variable-frequency train stimulation of human skeletal muscles
C Scott Bickel1, Jill M Slade, Gordon L Warren
1Department of Exercise Science, The University of Georgia, 300 River Rd, Athens, GA 30602, USA. cbickel@coe.uga.edu
Physical Therapy
|April 1, 2003
Summary
Electrical stimulation protocols for quadriceps femoris (QF) and tibialis anterior (TA) muscles can be applied interchangeably. Variable-frequency train (VFT) stimulation enhances force in fatigued muscles, regardless of fiber type composition.
Area of Science:
- Neuromuscular electrical stimulation
- Skeletal muscle physiology
- Exercise rehabilitation
Background:
- Quadriceps femoris (QF) and tibialis anterior (TA) muscles have different fiber-type compositions.
- Electrical stimulation protocols are commonly used but may not account for fiber-type differences.
Purpose of the Study:
- To test if torque augmentation differs between QF and TA muscles using variable-frequency train (VFT) versus constant-frequency train (CFT) stimulation.
- To investigate if VFT stimulation is effective for fatigued muscles with varying fiber types.
Main Methods:
- Ten healthy men participated.
- Subjects' TA and QF muscles were stimulated using CFT and VFT protocols to evoke isometric contractions.
Main Results:
- VFT stimulation did not differ from CFT in torque-time integral or peak torque post-potentiation.
- After fatigue, VFT enhanced torque-time integral by 25% similarly in both QF and TA muscles.
- VFT evoked greater peak torque and less slowing of rise time compared to CFT in fatigued muscles.
Conclusions:
- Torque augmentation by VFT stimulation is effective for fatigued human skeletal muscle, irrespective of fiber type.
- QF and TA muscles may not exhibit significant differences in fatigue resistance under these stimulation conditions.