This isn't breaking news, but I think it's interesting. While looking through somepresentations from last year's Pan Pacific Conference of Medicine and Science in Sport (for a story I'm working on), I stumbled across John Hawley's presentation, "Endurance and Strength Training: Are They Incompatible?" I've written about this topic before – in fact, the title of my book, "Which Comes First, Cardio or Weights?", refers to this dilemma. But it remains an area of active research, and Hawley's presentation does a great job of bringing together some interesting recent findings.
The whole presentation is worth a look if you're interested in the topic, but I want to highlight three figures taken from a 2012 meta-analysis of 21 concurrent training studies by a team led by Jacob Wilson and his colleagues, published in the Journal of Strength and Conditioning. (The figures are actually much easier to read in Hawley's presentation, but I'm showing the originals below.) They each compare various training options by showing the standardized effect sizes, giving a sense of which factors matter most.
(1) The first one is a general overview, showing the effect size of strength training alone, endurance training alone, or the two combined on various parameters (lower body hypertrophy, strength, power, VO2max, and body fat).
The results are pretty much what you'd expect – for muscles, combined training is better than no strength training but not as good as only strength training. The biggest surprise is that VO2max gains were essentially identical with and without strength training, suggesting that endurance athletes shouldn't worry about losing out on endurance gains if they add strength training. (Obviously this finding is specific to the protocols used in the studies analyzed, but it's still interesting.)
(2) The second graph shows that not all "endurance" training is the same. Running and cycling have quite different effects:
Wilson et al. offer some theories about why running seems to interfere with strength and muscle gains more than cycling. One is that the cycling motion is more similar to the movements used in strength training (and strength assessment); the other is that running, with its large component of eccentric muscle contraction, produces more muscle damage that interferes with muscle and strength gains. Hard to know which, if either, of these ideas is true, but the results are certainly interesting. Note also that running packs a larger punch in VO2max and body fat loss – perhaps the running protocols in the studies analyzed were simply harder?
(3) The third graph looks for (and finds) a dose-response relationship between the amount of endurance training and the decline in effect size for hypertrophy, strength, and power gains.
Again, not surprising, but interesting to see quantified. Hawley's presentation also outlines some other interesting avenues of research, like the prospect that sufficient protein can reduce the interference effect between the molecular signals stimulated by endurance and training training. As I said, it's worth a look!