ABSTRACT
On the bicycle, the human upper extremity has two essential functions in steering the bicycle and in supporting the body. Through the handlebar, surface- induced loads are transmitted to the hand and arm of the bicycle rider under vibration exposure conditions. Thus, the purpose of the study was to investigate the effect of vibration exposure on forearm muscle activity for different road surfaces (i.e. smooth road, concrete stone pavement, rough road) and for different bicycles. Ten subjects participated in experiments and two types of bicycles, i.e. Road Bike (RB) and Mountain Bike (MTB) are compared. The acceleration magnitudes were dominant along x and z-axes. The r.m.s acceleration values in the z direction at the stem of MTB were at most 2.56, 7.04 and 10.76 m·s(-2) when pedaling respectively on asphalt road, concrete pavement and rough road. In the case of RB the corresponding values were respectively 4.43, 11.75 and 27.31 m·s(-2). The cumulative normalized muscular activity levels during MTB trials on different surfaces had the same tendency as with acceleration amplitudes and have ranked in the same order from lowest to highest value. Although road bike measurements have resulted in a similar trend of increment, the values computed for rough road trials were higher than those in MTB trials. During rough road measurements on MTB, rmsEMG of extensor muscles reached a value corresponding to approximately 50% of MVC (Maximum Voluntary Contraction). During RB trials performed on rough road conditions, rmsEMG (%MVC) values for the forearm flexor muscles reached 45.8% of their maximal. The level of muscular activity of forearm muscles in controlling handlebar movements has been observed to be enhanced by the increase in the level of vibration exposed on the bicycle. Since repeated forceful gripping and pushing forces to a handle of a vibratory tool can create a risk of developing circulatory, neurological, or musculoskeletal disorder, a bicycle rider can be considered vulnerable to developing vibration related overuse injuries and/or performance diminishing consequences. Key PointsThe muscular activity level in the forearms increases in response to random vibration transmitted to the bicycle to control handlebar movements.The level of vibration transmission depends on irregularities on road surface and bicycle type.A bicycle rider can be considered vulnerable to developing vibration related overuse injuries and/or performance diminishing consequences.
ABSTRACT
UNLABELLED: Vibration analysis seldom has been used in detecting structural and mechanical changes in physiologic and pathologic bone conditions. We sought to correlate natural frequency of the radius measured by vibration analyses with bone mineral density measured by dual-energy xray absorptiometry and quantitative computed tomography (including cortical thickness). Sixty sedentary men between 50 and 70 years old were deemed osteopenic or healthy. A higher natural frequency of the dominant and nondominant radius was seen in the healthy men compared with the osteopenic men. Natural frequency was consistent with bone mineral density in dominant and nondominant radius in both groups. Moreover, there was a correlation between bone mineral density measured by dual-energy xray absorptiometry and natural frequency in the dominant and nondominant radius. Cortical thickness of the dominant and nondominant radius also correlated with natural frequency. We concluded natural frequency measured by vibration analysis is a precise method for the assessment of structural properties of bone and correlates with the bone mineral density of the radius. LEVEL OF EVIDENCE: Diagnostic study, Level II (Testing of previously developed diagnostic criteria on consecutive patients [with universally applied reference "gold" standard]). See the Guidelines for Authors for a complete description of the levels of evidence.
