2b.

Serum concentrations of L- and D-BAIBA in different age populations

Aminobutyric acids	Measurements	Physical performance	Age group
			20–34 yrs	35–49 yrs	50–64 yrs	65+ yrs	p-value
D-BAIBA (μM)	All participants in each group	All	1.38 ± 0.62 (30)	1.51 ± 0.65 (30)	1.47 ± 0.67 (30)	1.77 ± 1.03 (30)	0.2374
		High (HP)	1.54 ± 0.79 (10)	1.43 ± 0.40 (10)	1.56 ± 0.87 (10)	2.07 ± 1.41 (10)	0.4432
		Average (AP)	1.31 ± 0.56 (10)	1.63 ± 0.69 (10)	1.38 ± 0.66 (10)	1.51 ± 0.56 (10)	0.662
		Low (LP)	1.30 ± 0.53 (10)	1.48 ± 0.83 (10)	1.46 ± 0.48 (10)	1.73 ± 0.98 (10)	0.6314
L-BAIBA (μM)	All participants in each group1	All	0.025 ± 0.028 (30)	0.041 ± 0.044 (30)	0.052 ± 0.066 (30)	0.052 ± 0.085 (30)	0.2572
		High (HP)	0.037 ± 0.030 (10)	0.038 ± 0.036 (10)	0.029 ± 0.028 (10)	0.033 ± 0.030 (10)	0.9048
		Average (AP)	0.0052 ± 0.016 (10)	0.047 ± 0.064 (10)	0.081 ± 0.106 (10)	0.084 ± 0.140 (10)	0.2243
		Low (LP)	0.033 ± 0.027 (10)	0.038 ± 0.028 (10)	0.048 ± 0.027 (10)	0.039 ± 0.038 (10)	0.7553

For the participants with L-BAIBA undetectable in their serum samples, the L-BAIBA levels are counted as “0”.