At Mend we provide many treatments to our Boulder Physical Therapy patients, but strength training is the common treatment between all patients and conditions. Often we prescribe an effective resistance training exercise leading to quick gains in strength. This rapid increase in strength over the first 6-8 weeks of an exercise program is due to nervous system, not muscle, adaptations to the exercise. These adaptations include improved communication between nerves and muscles, coordination of muscle firing, and effort by the nervous system to complete the exercise. As the new exercise is performed each week beneficial effects are noted throughout the body.
Previous research has shown improved balance and strength in limbs, which were or were not exercised. For example, patients given a right leg balance exercise improved their balance on the right side, as well as, on the left. In turn patients who were given a left leg strengthening exercise also showed strength gains on the right side. The mechanism behind these strength gains is called cross education and involves the nervous system’s ability to coordinate the movement required during the exercise. Untrained limbs demonstrate up to 20% strength gains after completion of the trained limbs exercise program (Munn et al. 2004).
A recent study was conducted on cross education to determine the impact of a 4 week unilateral strength training program on the untrained side. After 4 weeks of training strength gains were noted in both the trained and untrained legs, but greater gains were noted in the trained limb. Consistent with prior research only the trained limb demonstrated improvements in muscle size and thickness indicating the untrained limbs gains were mainly due to nervous system adaptations.
This study adds support to the importance of exercising both limbs when learning a new exercise. Exercising each side of the body helps establish necessary nervous system adaptations, which lay the groundwork for future muscle growth and strength. Additionally, athletes and patients who are unable to exercise due to injury, immobilization, or weight bearing status are encouraged to exercise their uninvolved limbs. This allows the body to maintain strength and attenuate the negative effects of immobilization such as muscle atrophy.
To learn more about how cross education can help accelerate your return from injury contact your local Physical Therapist