Table 1.

Effect of hindlimb unloading on muscle mass of adult and old rats

	Control	3-day HU	7-day HU	14-day HU	%Loss from Control after 14 Days
TA
Adult	0.779 ± 0.043	0.659 ± 0.066*	0.659 ± 0.053*	0.625 ± 0.046*	−19.8
	(1.895 ± 0.072)	(1.776 ± 0.062)	(1.799 ± 0.056)	(1.803 ± 0.074)
Old	0.741 ± 0.059	0.671 ± 0.048	0.655 ± 0.037	0.630 ± 0.061*	−15.0
	(1.304 ± 0.163)#	(1.265 ± 0.078)#	(1.376 ± 0.067)#	(1.260 ± 0.070)#
EDL
Adult	0.191 ± 0.007	0.168 ± 0.018	0.169 ± 0.008	0.157 ± 0.010*	−17.7
	(0.460 ± 0.026)	(0.452 ± 0.013)	(0.462 ± 0.025)	(0.453 ± 0.015)
Old	0.188 ± 0.019	0.174 ± 0.013	0.175 ± 0.010	0.172 ± 0.014	−8.9
	(0.330 ± 0.037)#	(0.330 ± 0.037)#	(0.367 ± 0.021)#	(0.344 ± 0.028)#
Soleus
Adult	0.178 ± 0.013	0.166 ± 0.013	0.132 ± 0.007*	0.111 ± 0.020*	−37.9
	(0.437 ± 0.028)	(0.447 ± 0.012)	(0.360 ± 0.013)*	(0.318 ± 0.045)*
Old	0.167 ± 0.016	0.152 ± 0.013	0.140 ± 0.010*	0.117 ± 0.010*	−29.8
	(0.293 ± 0.033)#	(0.286 ± 0.030)#	(0.294 ± 0.016)#	(0.235 ± 0.017)*,#
PLN
Adult	0.414 ± 0.041	0.365 ± 0.044	0.352 ± 0.022*	0.306 ± 0.017*	−26.3
	(1.018 ± 0.096)	(0.981 ± 0.068)	(0.962 ± 0.047)	(0.883 ± 0.047)*
Old	0.392 ± 0.016	0.334 ± 0.017*	0.332 ± 0.027*	0.309 ± 0.030*	−21.7
	(0.692 ± 0.098)#	(0.632 ± 0.069)#	(0.697 ± 0.058)#	(0.618 ± 0.027)#
MG
Adult	0.938 ± 0.061	0.790 ± 0.098*	0.749 ± 0.049*	0.643 ± 0.043*	−31.4
	(2.288 ± 0.129)	(2.122 ± 0.092)	(2.047 ± 0.082)	(1.870 ± 0.122)*
Old	0.872 ± 0.064	0.759 ± 0.055*	0.653 ± 0.021*,#	0.625 ± 0.061*	−28.3
	(1.536 ± 0.205)#	(1.436 ± 0.145)#	(1.390 ± 0.092)#	(1.252 ± 0.068)*,#

Muscle masses are means ± SD in g. In parentheses, muscle mass is normalized to body weight (mg wet mass/g body wt) and expressed as means ± SD; n = 6–7/group. HU, hindlimb unloading; TA, tibialis anterior; EDL, extensor digitorum longus; PLN, plantaris; MG, medial gastrocnemius.

^*P < 0.05 vs. age-matched control.

^#P < 0.05 vs. adult at same time point.