Does insulin-like growth factor 1 genotype influence muscle power response to strength training in older men and women?

Abstract

The CA-repeat polymorphism in the insulin-like growth factor 1 (IGF1) gene promoter region has been associated with strength and circulating IGF-I protein levels. The purpose of the study was to determine if the IGF1 CA-repeat polymorphism influences muscle power at baseline and in response to ST in older adults. Knee extensor peak power (PP) was measured at 50, 60, and 70% of 1-RM strength before and after 10 weeks of unilateral knee extensor ST in older adults, aged 50-85 years, to determine the changes in absolute and relative PP with ST. Subjects (N = 114) were genotyped for the IGF1 CA-repeat polymorphism and grouped as homozygous for the 192 allele, heterozygous, or non-carriers of the 192 allele. The 192 homozygotes had significantly lower baseline PP at 50, 60, and 70% of 1-RM strength than the non-carriers when age, sex, and baseline fat-free mass were covaried (all P < 0.05). This same relationship was observed when the highest PP within these ranges was compared (e.g., 317.6 ± 13.5 for 192 homozygotes and 380.2 ± 16.3 for non-carriers of the 192 allele, P < 0.05). Both absolute and relative PP increased significantly with ST in all genotype groups as expected, but there were no significant relationships among IGF1 genotypes and any of the PP changes. Despite a significant relationship between IGF1 genotype and knee extensor peak power at baseline, IGF1 genotype does not appear to influence changes in knee extensor peak power with ST.

Narrative Review of Sex Differences in Muscle Strength, Endurance, Activation, Size, Fiber Type, and Strength Training Participation Rates, Preferences, Motivations, Injuries, and Neuromuscular Adaptations

“…Researchers have also used imaging techniques to measure sizes of muscles of the upper limbs (Figure 16 and Table 21, Supplemental Digital Content, http://links.lww.com/JSCR/A339), lower limbs (Figure 17 and Table 22, Supplemental Digital Content, http://links.lww.com/JSCR/A339), and trunk (Figure 18 and Table 23, Supplemental Digital Content, http://links.lww.com/JSCR/A339) in men and women (2–5,7–10,15,17,24,26,30,51,79,99,153,155,176,189,202,217,219,232,234,254,273,284,296,308,309,313,325,335,337,339,368,369,390,395,399,403,409,428,432,437,438,452,455,456,465,467,470,474,478,480,481,494,495,497). Sex differences are obvious in all muscle groups but are larger for upper-body than lower-body muscles.…”

“…Many researchers have used imaging techniques to measure muscle mass in men and women (6,90,112,158,216,220,223,237,245,248,255,260,263,264,(270)(271)(272)(273)(274)278,341,347,365,412,419,420,428,471,474,497). Figure 14 and Supplemental Digital Content (see Table 18, http://links.lww.com/JSCR/A339) present the results of total lean body mass (LBM), total fat-free mass (FFM), total skeletal muscle mass (SMM), and total appendicular SMM.…”

“…Researchers have also used imaging techniques to measure sizes of muscles of the upper limbs (Figure 16 155,176,189,202,217,219,232,234,254,273,284,296,308,309,313,325,335,337,339,368,369,390,395,399,403,409,428,432,437,438,452,455,456,465,467,470,474,478,480,481,494,495,497). Sex differences are obvious in all muscle groups but are larger for upper-body than lower-body muscles.…”

“…Numerous articles have included sex-segregated data for muscle groups other than those used for hand gripping (5,10,12,14–16,20,22,26–29,31,33–35,45,48,49,53,55,63,64,68,71,75,77,80,81,82,85,93–95, 100,101,109–112,114–116,126,129,142,144,150,156,160,164,166,168,172,174–176,178,180–182,190,192,194,195,199,202,207,208,212–214,219,224,231,236,238–240,246,247,250,252,253,256–259,261,262,267–269,273–277,286,289,291,293,295–301,305,310,313–315,318,319, 323,325,326,335,338–340,342–344,346–349,351,353,354,365,367,369,370,376,377,379–384,386,390,392,394,396,397,400,401,408,410,411,413–415,417,424,425,427–429,442,443,445,447,449–451,453–455,457,460,462–464,468,470,474–476,481,483,485,486,488–490,492,494–496,498,499,502).…”