Isokinetic assessment in ALS

These data demonstrate significant changes in various measures of motor function. Activity based as well as isokinetic tests independently demonstrated pronounced reductions in abilities over time in this population of patients with ALS. That the changes demonstrated by isokinetics were different than the changes demonstrated by functional timed testing is to be expected. Certainly, the ability to walk includes more complex factors than strength generation about the knee joint. Similar truths exist about arising from a chair or taking a step up. More surprising is that significant correlations exist between timed walking and knee flexor torque production at 180° per second. This finding was unexpected in that it demonstrates a statistical association between a nonweight bearing activity and an activity generally accepted as requiring antigravity capabilities. Thus, we would have expected the better correlation to exist between knee extensors (antigravity muscles) and walking velocity. This leads to several new and testable hypotheses regarding walking in patients with ALS. First, patients with ALS may be using a different motor program to maintain ambulation as evidenced in other disorders with UMN findings. With the selective loss of some muscles and not others, there may be substitution of different timings and activations. This would need to be assessed with multiple electromyographic tracings or the measurements of reciprocal inhibition time on the isokinetic dynamometer goniograms. A related problem that we may be assessing indirectly is the need to develop tension quickly in order to stabilize the knee at heel strike. Perhaps rather than measurements of peak torque, the time-tension development of the torque curve would be a better measure. A subpart of this speculation is that specific muscle strength requirements change dependent on other muscle strengths and it may be those changes that we are seeing in our data. Second, there may be pathologically determined new programs based on the UMN part of the disorder. There is indeed evidence that in patients with spasticity, there are abnormally timed cocontractions. Unfortunately many of these measures require more sophisticated machinery including digitization capability and multiple channel recordings with their attendant increases in cost and time to decipher the meanings of the recordings.