Table 2.

Effect of pH 6.2 + 30 mM P_i on velocity and force in type I and II fibers

	n	Vo, fl/s	Vmax, fl/s	a/Po	Vopt, fl/s	Popt, kN/m2
Type I fibers, condition
15°C pH 7	14	1.89 ± 0.09	1.53 ± 0.09	0.07 ± 0.01	0.31 ± 0.02	23.5 ± 1.4
15°C pH 6.2, 30 mM Pi	14	1.00 ± 0.18*	1.16 ± 0.09*	0.08 ± 0.03	0.23 ± 0.01*	11.4 ± 0.9*
%Change		−47	−24	13	−26	−51
30°C pH 7	12	8.00 ± 0.74	4.23 ± 0.12	0.27 ± 0.06	1.25 ± 0.07	41.4 ± 2.4
30°C pH 6.2, 30 mM Pi	12	6.11 ± 0.79	3.58 ± 0.17*	0.20 ± 0.09	0.91 ± 0.09*	20.6 ± 1.1*
%Change		−24	−15	−26	−27	−50
Type II fibers, condition
15°C pH 7	20	5.97 ± 0.78	3.37 ± 0.30	0.21 ± 0.04	0.85 ± 0.15	27.0 ± 2.4
15°C pH 6.2, 30 mM Pi	20	3.58 ± 0.50*	2.31 ± 0.40*	0.28 ± 0.07	0.83 ± 0.19	11.8 ± 1.5*
%Change		−40	−31	25	−2	−56
30°C pH 7	13	13.48 ± 1.00	6.24 ± 0.56	0.56 ± 0.08	2.38 ± 0.15	43.8 ± 3.5
30°C pH 6.2, 30 mM Pi	13	8.76 ± 0.90*	4.55 ± 0.48*	0.59 ± 0.09	1.74 ± 0.15*	25.4 ± 2.5*
%Change		−33	−31	5	−27	−39

Values are means ± SE n, number of fibers studied where type I and type II fibers were isolated from 4 and 6 rats, respectively. V_o, maximal shortening velocity determined from slack test; V_max, maximal unloaded shortening velocity determined from the Hill plot test; a/P_o, unitless parameter describing curvature of the force-velocity relationship; V_opt and P_opt, velocity and force at peak power

^*Significantly different from pH 7, P < 0.05. At both pH 7 and pH 6.2, 30 mM P_i, all values at 30°C were significantly higher than 15°C.