Figure 4. Force during a shortening after concentric and eccentric contractions.

Shortening force and isometric force before the shortening are given as fractions of the isometric force measured at optimum length at the start of the experiment using a rate of 140 pps stimulation. □, unexercised muscle, ○, muscles fatigued using concentric contractions, •, eccentric contractions carried out on fatigued muscles, ▪, eccentric contractions carried out on unfatigued muscles. The dotted line indicates the relation if the fall in shortening force was proportional to the fall in isometric force. The coarse dashed line is drawn through points for 140 pps values for the control muscles and after eccentric, concentric or both kinds of contraction. The slope of the line was 0.44 ± 0.02. For the unfatigued muscle values are also shown for 50 pps and 80 pps simulation rates. Here the smaller symbols are for the lower stimulation rates. These values have the fine dashed line drawn through them (slope 1.30 ± 0.13).