To the Editor: Dr Ylinen and colleagues1 found that both strength (isometric) and endurance (isotonic) training were superior to a control regimen of stretching and aerobic exercise for relieving chronic neck pain. The authors also found that isometric training improved strength more than did isotonic training.
I have 3 concerns about this study. First, isometric training is most specifically designed to increase the isometric strength of particular muscles.2 Thus, use of isometric strength as an outcome measure could result in significant bias in favor of the isometric group.
Second, there were other important differences between the experimental and control groups that may explain these results. Both isometric and isotonic groups received 9 practice sessions "to enable them to learn the program properly" whereas the control group was trained only once in the proper way to perform the exercise and subsequently received written instruction. Because the participants in the control group received less education, it is possible that their performance of and adherence to the exercise regimen differed from that of the other 2 groups.
Finally, the use of only an educational booklet in the control group may have also affected the outcome measures. For instance, Cherkin et al3 noted significantly greater disability at 1 year among those who received only an educational booklet to treat low back pain compared with those receiving active interventions such as physical therapy.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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