Table 1.

Values for metabolites from 7- and 30-month-old mouse hindlimb muscles

	7-month	30-month	P-value
ATP (mm)	6.88 ± 0.79	4.16 ± 1.01	0.09
PCr/ATP	3.37 ± 0.11	3.83 ± 0.33	NS
pH	7.13 ± 0.04	6.99 ± 0.03*	0.03
TCr (mm)	37.1 ± 3.3	37.5 ± 0.7	NS
PCr (mm)	22.4 ± 0.7	16.2 ± 1.3*	< 0.01
ADP (μm)	30.8 ± 6.8	58.0 ± 9.5*	0.05
ATP/ADP	275 ± 70	84 ± 16*	0.03

The first three variables were measured directly using either HPLC (ATP and TCr) or MRS (PCr/ATP and pH). The final four variables were derived as described in the methods. P-values were determined using a two-tailed unpaired t test. n = 5 for all values except 7-month-old ATP where n = 6.