Comparison of muscle activity between isokinetic and iso-inertial exercise

Resistance training plays a crucial role in musculoskeletal rehabilitation and athletic performance. Traditional resistance training often underloads the eccentric phase, as muscles generate more force while lengthening. Isokinetic and iso-inertial exercises have been used to overcome this limitation, with both showing greater muscle activity compared to traditional methods, potentially leading to enhanced strength and hypertrophy. However, limited research compares the two modalities. This randomised crossover study involved healthy adults between the ages of 18-45 years who performed isokinetic knee extensions and iso-inertial squats at fast and slow speeds. Electromyographic activity of the quadriceps was recorded, and the eccentric-to-concentric root-mean-square (RMS) ratio was calculated. Results showed that iso-inertial exercise at fast speeds led to a significantly greater eccentric-to-concentric RMS ratio in the rectus femoris (95 % CI 0.11 to 0.74; Cohen's d = 0.89) and vastus lateralis (95 % CI 0.07 to 0.55, Cohen's d = 0.75) compared to isokinetic exercise, with no difference in vastus medialis or at slow speeds. Conclusion: These findings indicate that iso-inertial exercise induces greater eccentric muscle activity in key quadriceps muscles at fast speeds, suggesting its potential for enhancing eccentric overload and muscle strength gains.