Rachel Nilwik

The decline in skeletal muscle mass with aging is mainly attributed to a reduction in type II muscle fiber size

BACKGROUND The loss of skeletal muscle mass with aging has been attributed to a decline in muscle fiber number and muscle fiber size. OBJECTIVE To define to what extent differences in leg muscle cross-sectional area (CSA) between young and elderly men are attributed to differences in muscle fiber size. METHODS Quadriceps muscle CSA and type I and type II muscle fiber size were measured in healthy young (n=25; 23 ± 1 y) and older (n=26; 71 ± 1 y) men. Subsequently, the older subjects performed 6 months of resistance type exercise training, after which measurements were repeated. Differences in quadriceps muscle CSA were compared with differences in type I and type II muscle fiber size. RESULTS Quadriceps CSA was substantially smaller in older versus young men (68 ± 2 vs 80 ± 2 cm(2), respectively; P<0.001). Type II muscle fiber size was substantially smaller in the elderly vs the young (29%; P<0.001), with a tendency of smaller type I muscle fibers (P=0.052). Differences in type II muscle fiber size fully explained differences in quadriceps CSA between groups. Prolonged resistance type exercise training in the elderly increased type II muscle fiber size by 24 ± 8% (P<0.01), explaining 100 ± 3% of the increase in quadriceps muscle CSA (from 68 ± 2 to 74 ± 2 cm(2)). CONCLUSION Reduced muscle mass with aging is mainly attributed to smaller type II muscle fiber size and, as such, is unlikely accompanied by substantial muscle fiber loss. In line, the increase in muscle mass following prolonged resistance type exercise training can be attributed entirely to specific type II muscle fiber hypertrophy.

Patients with type 2 diabetes show a greater decline in muscle mass, muscle strength, and functional capacity with aging.

BACKGROUND The loss of muscle mass with aging reduces muscle strength, impairs functional capacity, and increases the risk of developing chronic metabolic disease. It has been suggested that the development of type 2 diabetes results in a more rapid decline in muscle mass, strength, and functional capacity. OBJECTIVE To investigate the impact of type 2 diabetes on muscle mass, strength, and functional capacity in an older population. METHODS Muscle mass (DXA and muscle biopsies), strength (1-repetition maximum), functional capacity (sit-to-stand test and handgrip strength), and reaction time performance (computer task) were compared between 60 older men with type 2 diabetes (71 ± 1 years) and 32 age-matched normoglycemic controls (70 ± 1 years). Data were analyzed using ANCOVA to adjust for several potential confounders. RESULTS Leg lean mass and appendicular skeletal muscle mass were significantly lower in older men with type 2 diabetes (19.1 ± 0.3 and 25.9 ± 0.4 kg, respectively) compared with normoglycemic controls (19.7 ± 0.3 and 26.7 ± 0.5 kg, respectively). Additionally, leg extension strength was significantly lower in the group with type 2 diabetes (84 ± 2 vs 91 ± 2 kg, respectively). In agreement, functional performance was impaired in the men with type 2 diabetes, with longer sit-to-stand time (9.1 ± 0.4 vs 7.8 ± 0.3 seconds) and lower handgrip strength (39.5 ± 5.8 vs 44.6 ± 6.1 kg) when compared with normoglycemic controls. However, muscle fiber size and reaction time performance did not differ between groups. CONCLUSION Older patients with type 2 diabetes show an accelerated decline in leg lean mass, muscle strength, and functional capacity when compared with normoglycemic controls. Exercise intervention programs should be individualized to specifically target muscle mass, strength, and functional capacity in the older population with type 2 diabetes.

Elderly Men and Women Benefit Equally From Prolonged Resistance-Type Exercise Training

This study compares the effects of 6 months resistance-type exercise training (three times per week) between healthy elderly women (n = 24; 71±1 years) and men (n = 29; 70±1 years). Muscle mass (dual-energy x-ray absorptiometry-computed tomography), strength (one-repetition maximum), functional capacity (sit-to-stand time), muscle fiber characteristics (muscle biopsies), and metabolic profile (blood samples) were assessed. Leg lean mass (3% ± 1%) and quadriceps cross-sectional area (9% ± 1%) increased similarly in both groups. One-repetition maximum leg extension strength increased by 42% ± 3% (women) and 43% ± 3% (men). Following training, type II muscle fiber size had increased, and a type II muscle fiber specific increase in myonuclear and satellite cell content was observed with no differences between genders. Sit-to-stand time decreased similarly in both groups. Glycemic control and blood lipid profiles improved to a similar extent in both women and men. A generic resistance-type exercise training program can be applied for both women and men to effectively counteract the loss of muscle mass and strength with aging.

Protein Supplementation during Resistance-Type Exercise Training in the Elderly.

INTRODUCTION Resistance training has been well established as an effective treatment strategy to increase skeletal muscle mass and strength in the elderly. We assessed whether dietary protein supplementation can further augment the adaptive response to prolonged resistance-type exercise training in healthy elderly men and women. METHODS Healthy elderly men (n = 31, 70 ± 1 yr) and women (n = 29, 70 ± 1 yr) were randomly assigned to a progressive, 24-wk resistance-type exercise training program with or without additional protein supplementation (15 g·d-1). Muscle hypertrophy was assessed on a whole-body Dual-energy X-ray absorptiometry (DXA), limb (computed tomography), and muscle fiber (biopsy) level. Strength was assessed regularly by 1-repetition maximum (RM) strength testing. Functional capacity was assessed with a sit-to-stand and handgrip test. RESULTS One-RM strength increased by 45% ± 6% versus 40% ± 3% (women) and 41% ± 4% versus 44% ± 3% (men) in the placebo versus protein group, respectively (P < 0.001), with no differences between groups. Leg muscle mass (women, 4% ± 1% vs 3% ± 1%; men, 3% ± 1% vs 3% ± 1%) and quadriceps cross-sectional area (women, 9% ± 1% vs 9% ± 1%; men, 9% ± 1% vs 10% ± 1%) increased similarly in the placebo versus protein groups (P < 0.001). Type II muscle fiber size increased over time in both placebo and protein groups (25% ± 13% vs 30% ± 9% and 23% ± 12% vs 22% ± 10% in the women and men, respectively). Sit-to-stand improved by 18% ± 2% and 19% ± 2% in women and men, respectively (P < 0.001). CONCLUSION Prolonged resistance-type exercise training increases skeletal muscle mass and strength, augments functional capacity, improves glycemia and lipidemia, and reduces blood pressure in healthy elderly men and women. Additional protein supplementation (15 g·d-1) does not further increase muscle mass, strength, and/or functional capacity.