The main findings of this study are that, compared with controls, women with knee OA demonstrated higher H/Q moment ratios. Moreover, OA women showed higher VM/VL EMG activation ratios, but lower coactivation ratios than controls.
Many factors may explain the present findings. For example, people who display knee muscle weakness, such as people with knee OA, are characterized by fiber type II atrophy.48,49 In contrast, an increase in type I muscle fibers may increase muscle stiffness.50 This mechanism is adopted so that people with knee OA may decrease pain, although the relationship between muscle strength and pain is not always linear.51 Proprioceptive information is provided by the articular mechanoreceptors to the central nervous system,52 and it is necessary for neuromuscular control during dynamic efforts.53 Therefore, injury that results in loss of mechanoreceptors could decrease the reflex response and information transmission to the central nervous system, thus leading to changes in coactivation of quadriceps and hamstrings muscles.54–57 Previous research studies have showed that coactivation might be affected by age,58,59 gender32 and grade of OA,60 contraction velocity,24 type of muscle action28 and level of training.61 Future research could examine the individual and combined effects of these factors on muscle synergetic and antagonist activity in people with knee OA.
Isokinetic tests have a low relationship with muscle function during daily activities, such as walking, climbing stairs, or standing up from a chair. This is because maximum strength represents only 1 factor that determines functional performance. In previous studies, conventional strength ratios were found to be unsatisfactory predictors of functional capacity,5,62 functional ratios might be better predictors for stair climbing and descending in people with knee OA.5
Women with knee OA showed a higher H/Q moment ratio, higher VM/VL EMG ratio, and higher antagonist activation than asymptomatic individuals. Altered muscle activation during isokinetic tests may be a strategy that, used by people with knee OA, maintains knee joint integrity. In addition to quadriceps muscle strengthening, training programs could include exercises that enhance synergetic activity of the vastii muscles, better mobilize the patella, and provide improved coactivation balance of the antagonist muscle groups surrounding the knee.
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