Original Article Proc IMechE Part H: J Engineering in Medicine 1–11 Ó IMechE 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0954411918809141 journals.sagepub.com/home/pih The effect of saddle height and saddle position changes from pedal on muscles and joints behaviors in ergometer: A parametric study Elham Hazrati and Mahmood Reza Azghani Abstract The physical activities such as pedaling can affect the lower limb muscles strength and rehabilitation. Improper pedaling can cause injury. In this study, we would investigate the effects of saddle place (saddle position and saddle height) on the behavior of muscles and joints. Moreover, we would try to reveal the relationship between the muscles activity (Act) and the joints reaction forces (F) and saddle position and saddle height. To this end, the pedaling conditions are obtained from the biomechanical model of the human movement system presented in AnyBody software. The variations in 12 muscles Act and total, normal and shear F of ankle, knee and hip joints are studied for the various saddle places in the pedaling feasible range. The relationships of those muscles Act and joints F are predicted by the response surface method. The results indicate that the muscles and the joints behavior changes for various saddle position and saddle height. The maximum and the minimum of the total response are acquired in the ankle and hip joints, respectively. In contrast to the ankle and hip joints, the knee shear response is greater than the normal response. The predictive models of the muscles Act and the joints F (the regression coefficients (R 2 ) are 0.60–0.95 and 0.76–0.97, respectively) indicate their nonlinear behavior with saddle position and saddle height variations. Studying the muscles and joints behavior in dif- ferent pedaling condition can be helpful for the suitable saddle placement in order for rehabilitation, muscles soreness reduction, and joints disorder treatment. Keywords Cycling, musculoskeletal model, inverse dynamic analysis, predictive models, rehabilitation, injury risk Date received: 7 December 2017; accepted: 28 September 2018 Introduction Cycling is a recommended sport for elderly, overweight people, osteoporotic patients 1 and injured subjects after stroke 2 for rehabilitation. This exercise can impress the lower limb muscle strength, the cardiovascular perfor- mance and maintenance and the physical strength improvement. 1 The pedaling with ergometer has been recommended as a rehabilitation exercise 3 in many knee disorders including patellofemoral 4 and anterior cruciate ligaments (ACLs) injuries. 5 Improper pedaling conditions can increase the injury risk. 1,6 Several studies have been conducted on knee injuries including anterior knee pain and patellofemoral pain in sports medical centers. 7–9 The repetitive movements like pedaling can bring about injury since those activities cause the fatigue of ten- don or bone. Moreover, the pedaling is a repetitive movement in which the knee pain is a major problem. 10 Various factors affect the pedaling per- formance, which are classified into three groups as follows: 11–13  Environmental factors The environmental factors such as gravity, friction and air resistance are the general resistive forces that affect the cycling performance on land. 12,13 Department of Biomechanics, Faculty of Biomedical Engineering, Sahand University of Technology, Tabriz, Iran Corresponding author: Mahmood Reza Azghani, Department of Biomechanics, Faculty of Biomedical Engineering, Sahand University of Technology, PO BOX 51335/1996, Tabriz, Iran. Email: azghani@sut.ac.ir.