Background On Cross Education
Strength training of one limb causes an increase in voluntary strength in both limbs. This is known as “cross-education”, “cross-training”, or “contralateral-strength-training effect”. This phenomenon occurs in both the upper and lower extremities.
This strategy is commonly used when a limb is immobilized.
Sariyildiz et al. evaluated whether electrical muscle stimulation (EMS) on dominant wrist flexors causes an increase in muscle strength of the contralateral wrist extensors.
What was done
Twenty-three healthy, young, adult men were randomly placed in an EMS or control group. The EMS group passive wrist extension and EMS that caused powerful contraction were simultaneously applied. In the control group, transcutaneous electrical nerve stimulation was applied without causing any contraction.
Subjects were seated with 90-degree elbow flexion and supination. Then two large electrodes were placed over the flexor aspect of the right forearm (all participants were right-handed). Stimulation was applied for 30 sessions (one session a day, five days a week for six weeks).
The strength increases of the right wrist flexors muscles were on average 50.6% in the EMS group and were 6.2% in the control group. The strength increase of the left wrist flexor muscles was 44.1% in the EMS group and 11.7% in the control group. The strength increase of the right wrist extensor muscles was 67.3% in the EMS group and 18.1% in the control group. The strength increases of the left wrist extensors were 46.5% in the EMS group and 14.6% in the control group.
Results suggest that cross-education is not confined to the untrained contralateral wrist flexors and that the strength increase may also be observed in the contralateral wrist extensors.
This study indicates strength gains can occur on the opposite limb and antagonistic muscles. This is important in swimming if an athlete is injured, but they are able to train the other limb to prevent strength losses in both arms and all muscle groups. This also creates an important question: if an athlete injures their upper extremity and is only able to use their lower extremity, will the strength increase in the lower extremity training affect upper extremity strength? More research is required to confirm or rule-out this theory.
- Sariyildiz M, Karacan I, Rezvani A, Ergin O, Cidem M.Cross-education of muscle strength: cross-training effects are not confined to untrained contralateral homologous muscle. Scand J Med Sci Sports. 2011 Dec;21(6):e359-64.
Originally Posted June 2012