Why are slow-twitch muscles more beneficial than fast-twitch muscles for cardiorespiratory fitness? a. slow-twitch muscles are longer and thicker than fast-twitch muscles. b. slow-twitch muscles need less blood to contract than fast-twitch muscles. c. slow-twitch muscles need more recovery time between exercise sessions than fast-twitch muscles. d. slow-twitch muscles are able to use oxygen more efficiently than fast-twitch muscles.