Contractile impairment after quadriceps strength training via electrical stimulation

Area of Science:

• Exercise Physiology
• Neuromuscular Adaptation
• Rehabilitation Science

Background:

• Electrical stimulation (ES) is utilized for strength training, but its effects on neural and muscular adaptations, especially during detraining, require further investigation.
• Understanding the interplay between neural activation and muscle contractile properties is crucial for optimizing training protocols.

Purpose of the Study:

• To investigate the neural and muscular adaptations following 4 weeks of quadriceps electrical stimulation (ES) strength training and a subsequent 4-week detraining period in healthy active men.
• To determine the impact of ES training and detraining on maximal voluntary contraction (MVC) strength, neural activation, and muscle contractile properties.

Main Methods:

• Twenty healthy active men were randomized into an ES intervention group or a control group.
• The intervention group underwent 4 weeks of isometric quadriceps ES training (4 sessions/week, 20 min/session), followed by 4 weeks of detraining.
• Assessments included quadriceps MVC strength, neural activation (EMG), and excitation-contraction coupling properties before, after training, and after detraining.

Main Results:

• Maximal voluntary contraction (MVC) strength did not change post-training but increased significantly (+21.5%) after detraining.
• Neural activation and maximal EMG activity increased significantly post-training and remained elevated post-detraining.
• Quadriceps contractile properties were impaired post-training but recovered to baseline after detraining.

Conclusions:

• The initial lack of MVC strength gain after ES training resulted from a balance between increased neural activation and impaired muscle contractile function.
• Significant MVC strength gains after detraining were attributed to recovered contractile function and sustained neural activation.
• ES strength training may induce overreaching and delayed adaptations, suggesting cautious application in training programs for physically active individuals.