Inter-limb effects of isometric quadriceps strengthening on untrained contra-lateral homologous muscle of patients with knee osteoarthritis

PURPOSE: The primary objective of this study was to establish if there would be inter-limb crossing of strength from trained quadriceps muscles of unaffected limb to the untrained homologous group of muscles in subjects with knee osteoarthritis. METHODS: Twenty-one patients with knee osteoarthritis were recruited for the study. The affected knee was not trained while the unaffected quadriceps group of muscles was trained for 6 weeks using isometric contraction exercises. The patients sat on a quadricep bench with knee flexed to 90. as starting position. An ankle strap was used to fasten the required weight for isometric training at the lower one-third of the unaffected limb. Each patient extended the unaffected knee until the leg was fully straightened, maintaining quadriceps isometric contraction for 3 to 5 seconds; and then slowly returned to the starting position; 12 repetitions and 3 sets were performed thrice a week for 6 weeks. The peak isometric quadricep strengths of both limbs were quantified with spring balance at baseline and after 6 weeks. During quantification, all the patients were verbally motivated to achieve maximum voluntary contraction at extension. The data were analyzed using descriptive statistics of mean, standard deviation and percentages. Parametric inferential statistics of dependent t-test (paired) was used to compare the pre and post values obtained. RESULTS: The peak isometric quadriceps strength of the affected limb with knee osteoarthritis without training at baseline was 132.67 +/- 42.26 N while at the 6th week it was 159.30 +/- 49.33 N showing a significant increase of 20% (p = 0.001). For the trained unaffected knee, at onset and at 6th week, the peak isometric quadricep strengths were 158.83 +/- 43.28 N and 192.00 +/- 47.31 N respectively. There was significant increase of 21% in the quadriceps muscle strength of the unaffected knee after training (p = 0.001). However, there was no significant difference in the increments observed between the peak isometric quadriceps strengths of both limbs (p = 0.06). CONCLUSION: We concluded that there was cross training effect on the contralateral quadriceps muscle when only the ipsilateral (unaffected) homologous muscle was strengthened.