Abstract
Running is one of the most popular forms of exercise. Even though regular exercise is beneficial to human health, running is also often associated with an increased risk of injury. Lack of shock absorption in running shoes has often been stated as one of the main reasons for why running-related injuries have been on the increase. The aim of the present study was to assess the degree to which ground reaction forces (GRF) can be dissipated in the human leg in a barefoot subject, in connection with diverse physical activities. Acoustic myography (AMG), a non-invasive technique that records pressure waves from contracting muscles as well as the harmonic damping of ligaments, was applied to four anatomical sites on the subject’s leg, during barefoot walking, jogging, running and jumping. The data for walking on a hard surface show much lower ESTiTM parameters than those for the soft surface, and these lower values are observed mainly for sites 1 (toes; 65%) and 2 (ankle; 53%), respectively. AMG parameters for jogging reveal this gait to have very low ESTiTM parameters for site 1 and site 2 (ESTi 2 - 3), yet similar for both surfaces. The data for running on a hard and soft surface revealed much lower ESTiTM parameters (38%) than those for sites 3 (knee) and 4 (hip). The data from the big jump, reveal that on a hard surface, the lowest ESTiTM parameters were for sites 1 (toes; 46%) and 2 (ankle; 27%), compared to values on a soft surface. The speed with which GRFs were transmitted up the leg varied from site to site and also with the type of activity, ranging from undetectable to approx. 60 m/sec. The present study reveals that the ankle joint is exposed to the greatest forces during jumping and running. In addition, this study has confirmed that exercising on a hard surface does indeed increase the stress forces on the toes and ankles. It is interesting to note that the data reveal that toes and ankles absorb most of the GRF during running, while the knee and hip joint remain unaffected, although a more detailed study involving a larger number of subjects and shoe types is now needed.
Highlights
It is known that leg stiffness is constantly assessed and adjusted during periods of physical activity [1]
Whilst mechanical stress in the foot and lower limb can be alleviated by use of correct footwear [3], others have suggested that footwear per se may in itself reduce the activity patterns of supportive muscles compared with a barefoot state [4]
Acoustic myography (AMG) parameters The data obtained whilst walking on the hard surface show much lower E, S and T parameters than those for the soft surface, and these lower values are observed mainly for sites 1 and 2 (see Figure 1(a))
Summary
It is known that leg stiffness is constantly assessed and adjusted during periods of physical activity [1]. Ferris and coworkers [1] showed that human runners adjust the stiffness of their supportive leg during steady state running in accordance with the type of surface on which they are exercising. Tessutti and colleagues [7] reported that running on hard surfaces such as asphalt or concrete increases the peak pressure and decreases the contact time of a runner’s limb compared to running on grass. These authors went on the conclude that running on a grass surface with very little stiffness, may serve to allow the body to better attenuate forces by increasing contact time and decreasing stride length [8]. In a study of 15 recreational runners aged approx. 20 years (7 men; 8 women), measurements made during both fast and slow track runs revealed that the pronation excursion, the braking and the impact were significantly greater when compared to values from the same individuals whilst undertaking a grass run [6]
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