Commentaries on Viewpoint: Do we need to change the guideline values for determining low bone mineral density in athletes?

to the editor: The Viewpoint by Jonvik et al. (1) proposes to change the guidelines to interpret athletes’ bone mineral density (BMD) Z-scores in low- versus high-impact sports. This proposal is mainly based on the potential role of BMD as a marker of low energy availability (LEA)/relative energy deficiency in sport (RED-S). It can be argued, however, that the primary function of BMD measurements is to analyze the risk of (osteoporotic) fractures in an individual (2). In this regard, BMD Z-scores seem to be related to (stress) fracture risk, independent of sports discipline (3). Furthermore, achieving a high peak bone mass, and preventing low absolute BMD, in early adulthood may prevent osteoporosis and fractures later in life (4,5). These arguments do not support the use of sport-specific guidelines for the interpretation of BMD Z-scores. Nevertheless, we agree with Jonvik et al. (1) that high-impact sports could mask the presence of LEA/RED-S when using population-based Z-scores. Some potential pitfalls of this approach should be noted as well. First, the distinction between low- and high-impact sports is not always clear because low-impact sports can also include high-impact training. Second, sport-specific impact can differentially affect BMD status at various measurement sites. Finally, BMD changes occur slowly, which complicates the early detection and treatment of LEA by this instrument. In conclusion, sport-specific reference values could be a valuable adjunct in the diagnosis of LEA, but probably less important with regard to (stress) fracture risk. For early detection and prevention of LEA, research might need to focus more on the validation and use of objective blood markers.

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

to the editor: The effect of physical activity on bone mineral density (BMD) is not uniform across different sports (1). The net “osteogenic” effect of different sports is multifactorial and may be contingent on diverse physiological factors including, but not limited to, age and gender (2). In addition, genetic factors may also be at play. Protracted stretches of low energy availability (LEA) following engagement in sports may compound the problem (3,4), predisposing athletes to risk of osteoporosis and stress fractures.

In light of the present information, a blanket approach to identify athletes at risk of reduced bone mineral density (BMD) needs to be repudiated. There is a strong need to define activity-specific Z-scores for athletes. Also, the aforementioned miscellaneous determinants should also be cogitated upon.

This will facilitate early identification of at-risk individuals and enable institution of corrective measures. As proposed by Jonvik et al. (4), this is possible only by global congregation of sports and exercise physiology experts. Their collective efforts should culminate in generation of sport/event-specific cumulative data while also factoring in the other determinants. In a nutshell, there is a need for transition from a blanket to bracket approach for risk stratification using Z-scores.

No conflicts of interest, financial or otherwise, are declared by the authors.

to the editor: Jonvik et al. (1) discussed the importance of well-classifying bone mineral density (BMD) in people engaged in sports since scoring them with reference to a normal population does not seem valid. This is not the first time that the Journal of Applied Physiology presents commentaries on a viewpoint on BMD-related topics (2), highlighting the relevance of bone health in sports. However, we need to consider that the exposure to exercise varies according to the practitioners’ level (recreational, age-group, competitive, or elite), with the metabolic and mechanical loading affecting bone health differently due to the diverse 1) workout volume, intensity, density, and complexity and 2) recovery period strategies. Specifically in swimming, the voluminous general training period, the systematic exposure to the no-impact aquatic environment (training frequency is frequently greater than nine 2- to 3-h sessions/wk), and the very-high-intensity training sets of the specific and precompetition periods (3) might lead to significant low energy availability, causing low BMD. However, it is simplistic to define swimming as a low-impact sport since, in every training unit from young age, swimmers are involved in dry-land workouts aiming for strength development (4) and in in-water resistance exercises (with parachutes, drag suits, paddles, or fins). In addition, the starting and turning phases occupy ∼30% of the swimming distance total duration (5), meaning that swimmers push off the starting block and the turning wall systematically. Therefore, when developing a sport-specific BMD classification scale, sport level/expertise should be considered, and swimming (except for the open-water specialty) distinguished from other low-impact sports (e.g., cycling) and nonpractitioners.

No conflicts of interest, financial or otherwise, are declared by the authors.