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Does the Dose Do It?

Field-Fote, Edelle C. PT, PhD

Journal of Neurologic Physical Therapy: December 2009 - Volume 33 - Issue 4 - p 177-178
doi: 10.1097/NPT.0b013e3181c29abc
Editor's Note

Years ago I attended a lecture by a cardiologist who reviewed the evidence supporting low-dose aspirin therapy for prevention of vascular occlusion. He compared the recommended dose to the number of eyes that a person should have, saying “one’s not enough, and three’s too many.” After I stopped laughing over the images he evoked, I remember being awed by the precision of this dosing recommendation. Although the hubbub seems to have subsided over the recent meta-analysis concluding that low-dose aspirin therapy actually has doubtful benefit for prevention of occlusive events when weighed against the risk of bleeds,1 the issue is a reminder about the importance of appropriate dosing. Questions of dosing are crucial to most areas of medicine and health; think of the American College of Sports Medicine/American Heart Association’s2 joint guidelines for physical activity: 30 minutes of moderately intense cardio five days per week or 20 minutes of vigorously intense cardio three days per week, plus eight to 10 strength-training exercises eight to 12 repetitions of each exercise two days per week.2 Of all the different interventions that we can recommend as neurologic physical therapists, for how many can we make dosing recommendations that even come close to this level of specificity?

When our interventions fail to elicit a meaningful change in the motor performance or function of our patients, one conclusion might be that the intervention that we selected was not the best choice. In fact, at first glance, this may seem to be the case for overground gait training in individuals with chronic stroke as described in the systematic review by States et al in this issue of JNPT. But is the question really whether overground gait training is effective for improving walking function? Perhaps the real question is whether the dose that we typically use is sufficient to effect a change in function. Two years ago in this journal, Lang et al3 showed that individuals with stroke undergoing outpatient physical and occupational therapy take an average of 292 steps during a training session. This is approximately one tenth the number of steps taken per day by community-dwelling individuals with chronic stroke.4 How many steps per day can we really consider an adequate training dose?

We all know the adage “practice makes perfect.” In this issue of JNPT is a study by Malouin et al who show that sit-to-stand and stand-to-sit practice over 12 sessions with 120 repetitions each session is not sufficient (in the absence of added mental practice) to effect a change in performance. In animals studies of motor learning hundreds and, in many cases, thousands of repetitions of a behavior or task are performed before significant change in performance is observed. In human subjects, repetition alone, even without skill training, results in neuroplastic changes.5 However, it is unlikely that skill training alone, in the absence of adequate repetition, has a similar effect. The nervous system is plastic and amenable to training, and there is ample research to suggest that the key element is the opportunity for practice. How much practice does it take to perfect movement?

At a recent symposium, a colleague introduced the keynote speaker, a renowned scientist, by recounting a conversation they had had early in this colleague’s career. When asked for advice about how to map out one’s future in research, the scientist responded “There are scientists who plant trees, and there are scientists who decorate trees. You need to decide which you want to be.”6 The implicit message was that although there is some value in building on others’ momentous discoveries, it is the momentous discoveries that are of greatest value. My first reaction to this message was that of course everyone wants to be the one to “plant the trees”—to make the earth-shaking discoveries that result in a paradigm shift, those that result in a new way of thinking about the question, or an entirely new approach to the issue at hand. But the more I think about it, the more convinced I am that this is not always the case. In fact, I would suggest that within the realm of neurologic physical therapy practice and research, the most pressing questions are not “is xx the best approach?,” but rather questions such as “with what intensity does my patient need to practice xx?,” “how long should my patient practice xx?,” “with what frequency my patient do xx?” For our patients, the answers to dosing questions like these may in fact be the most momentous discoveries.

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1. Antithrombotic Trialists’ Collaboration, Baigent C, Blackwell L, et al. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised trials. Lancet. 2009;373:1849–1860.
2. Haskell WL, Lee IM, Pate RR, et al. Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc. 2007;39:1423–1434.
3. Lang CE, MacDonald JR, Gnip C. Counting repetitions: an observational study of outpatient therapy for people with hemiparesis post-stroke. J Neurol Phys Ther. 2007;31:3–10.
4. Michael KM, Allen JK, Macko RF. Reduced ambulatory activity after stroke: the role of balance, gait, and cardiovascular fitness. Arch Phys Med Rehabil. 2005;86:1552–1556.
5. Halder P, Sterr A, Brem S, et al. Electrophysiologic evidence for cortical plasticity with movement repetition. Eur J Neurosci. 2005;21:2271–2277.
6. Ward SR. Introduction of Dr. Reggie Edgerton at the Section on Research Retreat. Pacific Grove, CA. 9 Aug 2009.


© 2009 Neurology Section, APTA