Interface forces on the seat during a cycling activity

Background The last several years have seen an increased interest in elucidating the causes of non-traumatic injuries specific to bicyclists. Injuries may include soreness of the pelvis, skin problems in the groin, erectile dysfunction, and impotence. Combined loading at the seat may be contributing factors to these injuries. Methods Vertical and shear loads were collected for 10 subjects cycling at 75 crank revolutions per minute (RPM) in a common fit position. External workload was held constant at 125 watts while force data were collected using a multi-axis load cell integrated under the seat of a standard bicycle. The crank arm angles at which the maximum forces occurred were obtained using a motion analysis system, and regions of rider contact with the seat were visualized with a pressure mapping system. Findings Measured vertical loads at the seat were greater than shear loads. Maximum mean vertical loads of 49–52% body weight, rearward shear loads of 11–12% body weight, and lateral shear loads of 4–5% body weight occurred at the seat. Associated timing angles referenced to the pedal position were also measured and averaged at the maximum and minimum loads. Interpretation Seat pressure mapping and blood flow have previously been used to study the interaction between bicyclists and their seats. This investigation focused on shear and vertical seat loads that may be contributing factors in injuries at the groin.