I am designating three studies for special emphasis in the August, 2016 MSSE. First, Nelson et al. investigated the accuracy of several popular activity monitors, the Fitbits One, Zip, Flex, and the Jawbone UP24, in different types of activities. They found that step estimates were highly accurate for sedentary activities as well as for ambulatory activities (e.g., walking, running) for all four monitors tested. However, both steps and caloric expenditure were underestimated by all activity monitors for household or chore-type activities (e.g., laundry, sweeping) as well as for cycling. Overall, their results indicate that the activity monitors tested may work better in individuals who spend high proportions of their day sedentary and/or performing ambulatory activities for leisure/exercise than for individuals who spend significant time doing chores or other nonsedentary, nonambulatory activities.
On a very different topic, McArdle disease is an interesting condition in which blood lactate levels do not rise with exercise intensity, yet this disorder is the paradigm of exercise intolerance. McArdle disease is caused by mutations (especially p.R50X) in both copies of the gene (PYGM) encoding muscle glycogen phosphorylase (myophosphorylase), which catalyzes muscle glycogen breakdown. However, the molecular alterations that cause exercise intolerance are not well understood. Morán and colleagues generated a McArdle mouse model (pygm p.R50X/p.R50X) that allowed mechanistic investigations. In their article, they compared the muscle tissue of McArdle, heterozygous and wild-type mice, and found that myophosphorylase deficiency affects sensory energetic pathways and also some evidence of oxidative damage and alterations in calcium handling but with no major impairment in oxidative phosphorylation or autophagy/ubiquitination pathways. Their data support the fact that patients' muscles adapt favorably to exercise training.
Finally, Arnal and coworkers investigated the effects of six nights of sleep extension on motor performance and associated neuromuscular function before and after one night of total sleep deprivation. A group of subjects who were not chronically sleep deprived stayed in bed an additional 2 h per night over 6 days and were able to get an average of 1.25 h more sleep per night. In the sleep extension condition, the time to exhaustion (isometric sustained contraction) was improved compared to the control condition and this change could not be explained by smaller reductions in voluntary activation, measured by both nerve and transcranial magnetic stimulation. The beneficial effect of sleep extension was associated with a reduced rating of perceived exertion after sleep deprivation. Although this needs to be confirmed in further studies, it is possible that the longer the exercise (endurance activity), the more beneficial sleep extension is, especially when the competition (e.g., ultraendurance activities) induces sleep deprivation.