News & Views from the Editor-in-Chief: Andrew M. Jones
December's issue of MSSE contains the usual eclectic but excellent mix of impactful exercise science and medicine, as exemplified by these three highlights.
Premature specialization in running may lead to underdevelopment of the skeleton and contribute to bone stress injuries (including stress fractures). In their paper entitled 'Enhanced Bone Size, Microarchitecture, and Strength in Female Runners with a History of Playing Multidirectional Sports', Warden and colleagues used state-of-the-art high-resolution peripheral quantitative computed tomography (HRpQCT) to show that female collegiate-level cross-country runners who played multi-directional sports when younger had enhanced bone microarchitecture and greater strength at their distal tibia and enhanced bone size and strength at the diaphysis of their fibula and 2nd metatarsal compared to runners who solely ran. Benefits were also observed at select 'high-risk' bone stress injury sites. These data indicate that those supervising youth athletes should encourage a delay in specialization in running and promote play in multi-directional sports, especially when younger, to build a more robust skeleton and potentially prevent bone stress injuries.
The association between muscle glycogen content and the capacity for prolonged endurance exercise is well established, but the importance for short-term high-intensity exercise is less well explored. This topic was addressed by Vigh-Larsen et al. ('The Role of Muscle Glycogen Content and Localization in High-Intensity Exercise Performance: A Placebo-Controlled Trial'), with special emphasis on single-fiber subcellular glycogen concentrations and Ca2+ kinetics. Eighteen young well-trained participants performed glycogen-depleting exercise followed by either a high- or low-carbohydrate intake during a 5-h recovery period. Subsequent impaired repeated sprint ability and increased ratings of exertion were found in the low carbohydrate group, in association with sustained glycogen depletion of a large proportion of single-fibers, especially of the glycogen pool stored within the myofibrils. The results on Ca2+ kinetics were less clear but in favor of the high-carbohydrate supplemented group. These results support an important role of muscle glycogen in high-intensity exercise tolerance, with depletion below a certain moderate level exacerbating fatigue development possibly due to more severe depletion at the single-fiber and subcellular level.
Many factors influence fat mass accrual during growth, but most studies lack direct measures of body fat and do not account for maturation. In 'A 4-year Mixed Longitudinal Study of Health Behaviors and Fat Mass Accrual during Adolescence and Early Adulthood', McConnell-Nzunga and Gabel with their colleagues addressed these gaps in their analysis of the mixed-longitudinal Healthy Bones III Study. Sex-specific multilevel models examined the influence of physical activity (PA) and sedentary time (by accelerometry), and energy intake on dual X-ray absorptiometry-derived total body fat mass across ages 9 to 21 years, while aligning boys and girls on a common maturational landmark, age at peak height velocity. In this cohort of mostly healthy weight youth, sex differences were observed in trajectories of fat mass accrual and PA. However, in both sexes, moderate-to-vigorous PA was negatively associated with fat mass accrual. The authors highlight the need to consider a sex/gendered approach to physical activity interventions aimed at preventing obesity.
Andrew M. Jones
University of Exeter