Dear Editor-in-Chief,
Running as one of the popular forms of cardiovascular exercise provides many potential health benefits for an aging population (see Kendall and Fairman [7] for a more detailed review). In order to understand potential mechanisms underlying risk factors related to running, Freedman Silvernail and colleagues (1) have compared kinematics, kinetics, and variability differences between young and older runners. They have carefully matched running speed between the groups. They observed kinematic differences at the hip joint and kinetic differences at the ankle and hip joints. However, contrary to their hypothesis, they failed to observe variability differences between the groups. Their own protocol might offer an explanation as to the reason their variability results were similar between the two groups.
The participants in the study of Silvernail and colleagues (1) wore laboratory shoes and were asked to run within 5% of 3.5 m·s−1 while targeting a force plate with their right foot. The uniformed shoes (6), the targeting (2), and especially the required running speed could potentially put constraints on their variability measures.
The preferred running speeds of the young and older group were presented in Table 1 (1) as 3.5 and 3.0 m·s−1, respectively. This is normal as the decline in running speed with aging is well documented in the literature (5). The protocol required the participants to run at 3.5 m·s−1, which is closer to the average of the young group’s preferred speed but outside one standard deviation (3.0 ± 0.3 m·s−1, estimated based on Table 1) of the average of the older group’s preferred speed. Although variability was calculated with a different method, our previous data suggested that variability of walking changes with walking speed (8). Furthermore, running variability increases when runners are not running at their preferred speed (4).
Movement variability provides a higher-level understanding of movement organization (1,3,8). It can also inform us about our body’s adaptability to changing movement conditions. The authors of this paper have identified this critical issue in their introduction and documented the different preferred running speeds during data collection but did not present the variability while participants ran at their preferred speed.
To study the health consequence of running as exercise, it is important to compare criterion measures at the same running speed. However, it also important to study these variables at the participant’s preferred speed. They would most like to run at their preferred speed while exercising after all. More importantly, testing at preferred running speed might reveal the older group running with reduced variability (4), which could relate to less adaptability and greater risk of injury (3).
Li Li
Key Laboratory of Exercise and Health Sciences
Ministry of Education, Shanghai University of Sport
Shanghai, CHINA
School of Health & Kinesiology
Georgia Southern University
Statesboro, GA
REFERENCES
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Hum Mov Sci. 2005; 24(2): 257–267.
