However, its muscle has to shorten faster to reach the given rotation speed. Thus, this muscle cannot generate as much muscle force as the muscle in the speed system. Analogies The trade-off between strength and speed is can be well compared with the gears of a bicycle. For example, for pure wrist flexion, one needs to activate the flexor carpi radialis and flexor carpi ulnaris which act as co-synergists by balancing the undesired radial and ulnar deviation. Changes in the moment arm of a muscle during movements, therefore, bring about relative changes in a muscle's mechanical advantage .
Physiological advantage refers to the length-force relationship of muscles.
At the optimum length, a muscle can be said to have a physiological advantage for producing force, which may also influence joint moment. During most joint movements, there is a trade off between physiological and mechanical advantage that reduces the independent influence that either factor might have on the joint moment. These muscles are situated in the forearm and thus also span the wrist. Thus these muscle must be considered as wrist flexors and extensors, respectively. Note that the tendons of these muscles run deep in relation to wrist musculature.