Figure 3
Effects of fatigue model parameters α τ1 and β τ1 on isometric and non-isometric contractions in one subject where β τ1 was higher than average. (A) Addition of β τ1 (dθ/dt) to α τ1 in Equation 8 brings force relaxation time constant, τ1, closer to pre-fatigue value (top), resulting in non-isometric predictions with a faster rate of fatigue (bottom). Thin solid black lines are measured values, just prior to (80°) and at end of extension. (B) For isometric contractions, removal of α τ1 in Equation 8 keeps τ1 constant at pre-fatigue value, resulting in isometric predictions with a faster rate of fatigue (FTI =force time integral). (C) A single isometric contraction shows that when α τ1 is included in isometric Equation 8, progressively slower twitch relaxation times increase the force of contraction. (D) Single non-isometric contractions show that addition of β τ1 (dθ/dt) to Equation 8 partially negates the effect of α τ1 . In A. and B. pairs of 50CFT and 12.5VFT testing trains were followed by 13x33CFT fatiguing trains. Contractions in (C) and (D) occurred at 0.7 min (dashed line) and 2.3 min (solid line). Non-isometric: 4.54 kg load, 250 μs pulse duration. Isometric: 600 μs pulse duration. Initial force-motion model parameters: A 90 = 2.10 N/ms, K m = 3.52e-01, τ 1 = 36.1 ms, τ 2 = 52.1 ms, τ c = 20 ms, R 0 = 2, a = −4.49e-004 deg-2, b = 3.44e-02 deg-1, V 1 = 3.71e-01 N/deg2, V 2 = 2.29e-02 deg-1, L/I = 9.85 kg-1m-1, F M = 247.5 N. Fatigue model parameters: τ fat = 99.4 s, α A = −4.03e-07 ms-2, α Km = −1.36e-08 ms-1N-1, α τ1 = 2.93e-05 N-1, β τ1 = 8.54e-04 ms deg-1N-1.