Described herein are systems and methods for favorably coordinating a timing relationship between a musculoskeletal activity cycle and a cardiac cycle of a user. A method may include repetitively detecting a signal that correlates to a blood volume in the user; determining an actual value of the signal that varies with the timing relationship; computing a trend of the actual value of the signal; and adjusting the movement guidance based on the trend of the actual value. A system may include a prompt device configured to provide recurrently a movement guidance to the user for guiding performance of the rhythmic musculoskeletal activity; a sensor configured to provide a signal that correlates to a blood volume in the user; and a processor configured to determine an actual value of the signal that varies with the timing relationship and to adjust the movement guidance based on the trend of the actual value.

An exercise apparatus includes a first cord, a second cord, and an adjustment mechanism. The first cord is pullable from and retractable around a first pulley. The second cord is pullable from and retractable around a second pulley. The adjustment mechanism allows for adjusting a pull-out tension provided by the first cord independently of a retraction tension provided by the first cord. The pull-out tension provided by the first cord is a tension provided by the first cord when the first cord is pulled from the first pulley. The retraction tension provided by the first cord is a tension provided by the first cord when the first cord is retracted around the first pulley.