June 2017 - Volume 49 - Issue 6

  • L. Bruce Gladden, PhD, FACSM
  • 0195-9131
  • 1530-0315
  • 12 issues / year
  • 6/81 in Sports Sciences
  • 4.041
​​​​​​​​​​​​​​​​​​​​​​For June's issue of the journal, I have selected three particularly interesting articles from quite different areas of investigation. First, Martinez-Valdes et al. examined changes in motor unit behavior following 2 weeks of either endurance (END) or high-intensity interval training (HIIT), using a novel technique of high-density surface electromyography (HDEMG) motor unit decomposition and tracking. The study revealed that both HIIT and END training induced similar improvements in cardiorespiratory fitness; however, the neuromuscular adaptations to training differed significantly. HIIT induced an increase in maximal knee extensor strength that was accompanied by increased vasti muscle motor unit discharge rates and HDEMG amplitude at high contraction levels, whereas END training induced a marked increase in knee extensor endurance at a lower force level, without any influence on HDEMG amplitude or motor unit discharge rates. These results suggest that HIIT and END training induce specific neuromuscular adaptations; such findings have important implications for exercise prescription.​​​

Next, I direct you to Webber and coworkers' investigation of recovery after knee arthroplasty. Despite reductions in pain, levels of moderate-to-vigorous physical activity (MVPA) do not change substantially after total knee replacement. What about sedentary behavior and light activity—do people find it easier to sit less and engage in more activity (even if not MVPA)? Discouragingly, they found no differences in daily sedentary time, number of long sedentary bouts, or minutes of light activity between people waiting for knee replacement and those one-year post surgery. Continued high levels of sedentary behavior put these individuals at increased risk for physical decline and cardiovascular disease. Additional education and rehabilitation (including behavior change strategies) are needed.

Finally, Wijndaele et al. estimated the potential mortality risk benefits of replacing leisure-screen-time (including TV viewing) with different discretionary activities in almost 0.5 million middle-age adults without major chronic disease, followed for almost 8 years. Their findings suggested that replacing small amounts of leisure-screen-time (e.g., 30 min·d−1) with everyday activities such as do-it-yourself home maintenance and improvement, and gardening could result in relevant mortality benefits. These may be important targets for adults for whom taking up exercise and strenuous sports (which show stronger mortality benefits) to replace screen-time seems less feasible. Assuming causality, they also estimated that 4%–15% of premature deaths in the UK could be avoided through such substitutions, depending on activity intensity. Given the ubiquitous nature of leisure-screen-time and the achievability of the proposed behavioral change scenarios, these findings are of great public health importance.


L. Bruce Gladden

School of Kinesiology
Auburn University

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