Poppendieck et al.
In the August 2013 issue of the journal International Journal of Sports Physiology and Performance, a German research group (Poppendieck et al. 2013) reviewed the existing scientific literature to investigate the question:"What are the effects of post-exercise cooling (duration, temperature, and type of cold application) on performance recovery in trained athletes?"
There were two interesting approaches that were conducted by the authors here at PEZ. First, the investigation focused on trained athletes only (competitive on a regional level, active at least three times per week, and with a VO2max >55 mL/kg/min), eliminating studies that utilized relative non-trained subjects.
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Second, they systematically analyzed the existing literature using a meta-analysis. This has become very popular in medical research. Let's see what this type of analysis is all about.
Meta-What?
The traditional review of literature qualitatively surveys different articles, but may be strongly biased by the author's choice of articles or inherent bias or beliefs. It may also be hard to qualitatively compare studies, each with their different methodologies.Meta-analyses instead statistically analyze a broad range of scientific studies to come up with an overall effect size or the expected difference from a manipulation (e.g. CWI improves sprint performance by 2.6-percent). One glaring benefit is that while only 10 subjects may be tested in one particular study, a meta-analysis may find 20 studies, each with 10 subjects, and calculates the effect size with the 200 subjects instead, making for a more powerful analysis.
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Key Methodology
I noted above that a traditional review rarely shows how the author comes up with the research they discuss—it has to be taken on trust that the author is presenting a balanced report. There is no hiding with a meta-analysis—the absolute key part is that the author MUST list in detail exactly how they searched the literature (e.g. what journals, databases, or key terms they used and when), as well as the parameters used to include or exclude studies in their analyses. In Poppendieck et al. (2013), the parameters included:- Trained athletes only (see above for definition).
- Only cooling interventions post-exercise (e.g. cooling + active exercise recovery excluded).
- Identical performance tests pre- and post-exercise (e.g. just measuring subjective pain or blood excluded).
- A control condition with passive recovery.
- At least 90 minutes between cooling intervention and the post-test to remove the potential benefits of pre-cooling on performance.
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