Sir,

This is likely to be the definitive trial on the effectiveness of pre-exercise stretching for some time, so it is important that it is carefully reported and analysed in this paper by Jamtvedt et al. I have a few questions.

t is stated that “two primary outcomes and 12 secondary outcomes were specified a priori in the analysis plan” but only the two primary outcomes and five secondary outcomes appear in the paper. Four secondary endpoints (three reported in the paper) are listed in the trial protocol registered with the Australian and New Zealand Clinical Trial registry, accessible here. Five
secondary endpoints (three reported in the paper) are listed in the protocol available on the trial website, accessible here. In that protocol the second of the two primary endpoints (time to injury) is subdivided in a number of ways that, with the exception of whether the participant sought help from a professional, differ from the analyses reported.

The reported secondary analysis of “time to injuries to muscles, ligaments and tendons” differs from the pre-specified secondary outcome in both protocols of “time to injuries that might be considered could be preventable by stretching”? In the website protocol it is stated that this “preventability” classification would be done without knowledge of the trial group. Can the authors clarify whether this was done?

Can they also clarify which outcomes were pre-specified in the analysis plan before the trial allocation code was broken, can they report all these outcomes, and state what adjustment was made for multiple tests of statistical significance?

These questions may sound pedantic, but the primary outcome for injury was negative. The apparent effect on muscle ligament and tendon injuries was of only modest statistical significance (P=0.03), and might disappear if adjustment was made for multiple significance testing. The apparent effect on the “bothersome soreness” is unavoidably susceptible to reporting bias in an open trial. The higher rate of dropout from follow-up at all time points in the experimental group, which appears unlikely to be due to chance, might bias the results in either direction.

As a participant, I was impressed with the trial organisation and design. Without reassurance that analysis and reporting were of an equally high standard, I remain fearful that the authors’ conclusion that “stretching … probably reduces the risk of some injuries and does reduce the risk of bothersome soreness”, is too strong.

Jim Thornton
Nottingham
June 2009