Effect of resistance training on muscle use during exercise

Area of Science:

• Exercise Physiology
• Magnetic Resonance Imaging
• Muscle Adaptation

Background:

• Resistance training enhances muscle strength and performance.
• Magnetic resonance (MR) imaging can detect exercise-induced changes in muscle physiology.
• Understanding muscle activation patterns is crucial for optimizing training.

Purpose of the Study:

• To investigate the impact of resistance training on exercise-induced contrast shifts in MR images.
• To determine if training reduces the muscle area showing contrast shift for a given load.
• To explore the role of neural factors in training-induced adaptations.

Main Methods:

• Nine males underwent a 9-week unilateral quadriceps femoris (QF) resistance training program.
• MR imaging quantified contrast shift (cross-sectional area with altered spin-spin relaxation time) pre- and post-training.
• Exercise tests at 50%, 75%, and 100% of maximum load were performed.

Main Results:

• One repetition maximum increased significantly in both trained and untrained QF muscles.
• Left QF cross-sectional area increased post-training, with no change in the right QF.
• Post-training, less QF area showed MR image contrast shift for all tested loads, indicating reduced muscle activation.

Conclusions:

• Short-term resistance training reduces the MR image contrast shift for a given exercise effort.
• This suggests that less muscle mass is recruited to perform the same task after training.
• The observed effects in both trained and untrained limbs suggest neural adaptations are a primary driver of these changes.