Table 4. Percent variability for muscle phenotypes attributable to IGF1 CA repeat, IGFBP3 A-202C, and PPP3R1 I/D gene polymorphisms.

Genotype	Individual Source	Combined Gene Effect	P Value
Percent variability for genotype for change in muscle strength with ST
IGF1	1.22	3.46 = 1.22 + ½ (4.48)	<0.01
IGFBP3	2.83	4.84 = 2.83 + ½ (4.02)	>0.05
PPP3R1	0.03	2.27 = 0.03 + ½ (4.48)	>0.05
IGF1 × PPP3R1	4.48		0.07
IGFBP3 × race	4.02		0.09
Percent variability for genotype for change in MV with ST
IGF1	2.04	N/A	0.32
IGFBP3	0.16	N/A	0.91
PPP3R1	3.23	N/A	0.06
Percent variability for genotype for change in MQ with ST
IGF1	0.95	3.71 = 0.95 + ½ (5.54)	<0.05
IGFBP3	1.28	N/A	0.51
PPP3R1	0.22	2.99 = 0.22 + ½ (5.54)	>0.05
IGF1 × PPP3R1	5.54		0.06

“Combined gene effect” was computed as the main effect plus one-half of any gene × gene interaction or gene × race interaction. For example for IGF1, combined gene effect is the IGF1 main effect (1.22) plus one-half of the IGF1 × PPP3R1 gene × gene interaction [1/2(4.48)]. The other half of the gene × gene interaction is credited to PPP3R1. N/A, combined gene effect could not be determined because there was not at least a trend for a significant gene × gene or gene × race interaction.