It was already known that muscle strength gains in one limb due to resistance training would transfer to the same muscle on the opposite side of the body. This is known as the cross-training effect.
However, the main aspect of this work is a muscle contraction that has been proven to be most effective. In this study, 36 sedentary young men immobilized their non-dominant arm by wearing an elbow cast for three weeks.
They were then divided into three equal groups: a concentric contraction group that raised a dumbbell using the stationary arm, an eccentric contraction group that lowered a dumbbell, and a control group that did no exercise (see definitions below).
With the arm immobilized, the concentric and eccentric groups performed six weightlifting sessions twice a week for three weeks. These sessions would see them perform five sets of six dumbbell curls with dumbbells corresponding to 20, 40, 40, 60, 60 and 80 percent of maximal strength over six sessions.
When the cast was removed, the no-exercise control group saw a greater than 15 percent decrease in strength in the immobilized arm. However, weightlifters saw little or no decrease in muscle strength of the immobilized arm.
The concentric group saw muscle strength decrease by up to 4 percent, but interestingly, muscle strength increased by 4 percent for the eccentric group, indicating a stronger cross-training effect. The researchers also measured muscle size in the immobilized arm.
The control group saw a decrease in muscle size of about 12 percent, while both concentric and eccentric muscle contractions counteracted muscle atrophy in the contralateral immobilized arm.
Strengthening the opposite side of the body can stop muscle wasting
Muscle size still decreased by 4 percent for the concentric group, while the eccentric group showed no decrease in muscle size.
All participants were asked to perform 30 eccentric squats with their immobilized arms after the cast was removed, and the researchers measured various indicators of muscle damage before, immediately after, and five days after the exercise.
The control group showed very severe muscle soreness and loss of strength after exercise, while the concentric group showed less damage. Again, the eccentric group saw the best results, with a protective effect strong enough to reduce peak muscle soreness by 80 percent compared to the control group, and by 40 percent in the concentric group.
It is now known that eccentric muscle contractions seem to be most effective in increasing muscle strength and size, even in very small doses.
It is important to investigate whether the results of this recent study can be replicated for other muscles and whether eccentric resistance training is effective in combating immobilization in real-life injuries such as ligament sprains or tears, bone fractures, and post-surgery.
Health care providers may recommend resistance training, and especially eccentric contractions, to minimize the negative effects of immobilization and reduce its impact on people’s lives.