The purpose of this study was to determine the contributions made by the leg muscle groups to the external mechanical work done in standing broad and vertical jumping. Six subjects were filmed jumping from a force platform. Linked-segment analysis and inverse dynamics methods were used to compute the muscle moments of force and power and work output created by these moments of force. Results support the principle that all three extensor moments of force summate in both types of jumping but that the sequence of contractions was not from proximal muscles to distal as is stated by the continuity principle. Instead all three extensor moments act simultaneously to produce leg extension. The contributions made by the three muscle groups were not the same for the two types of jumps. For the propulsive phase of the standing broad jump the contributions of the hip, knee, and ankle muscles were 45.9%, 3.9%, and 50.2%, respectively, whereas, for the vertical jump the contributions were 40.0%, 24.2%, and 35.8%, respectively. These results indicate that broad jumping utilizes the muscle groups differently than vertical jumping and show the importance of the hip and ankle musculature in the production of external work in jumping.