Dr. Taaffe et al., EFFECT OF RECOMBINANT HUMAN GROWTH-HORMONE ON THE MUSCLE STRENGTH RESPONSE TO RESISTANCE EXERCISE IN ELDERLY MEN, The Journal of clinical endocrinology and metabolism, 79(5), 1994, pp. 1361-1366
Normal aging is characterized by detrimental changes in body compositi
on, muscle strength, and somatotropic function. Reduction in muscle st
rength contributes to frailty and risk for fracture in the elderly. Al
though older adults increase muscle strength as a result of resistance
exercise training, the strength gains quickly level off, with only mo
dest increases thereafter despite continued training. To investigate w
hether age-related deficits in the somatotropic axis limit the degree
to which muscle strength can improve with resistance training in older
individuals, we conducted a double blind, placebo-controlled exercise
trial. Eighteen healthy elderly men (65-82 yr) initially underwent pr
ogressive weight training for 14 weeks to invoke a trained state. Subj
ects were then randomized to receive either 0.02 mg/kg BW.day recombin
ant human GH (rhGH) or placebo, given sc, while undertaking a further
10 weeks of strength training. Sequential measurements were made of mu
scle strength (one repetition maximum), body composition (dual energy
x-ray absorptiometry), and circulating levels of insulinlike growth fa
ctor-I (IGF-I) and IGF-binding protein-3. For each exercise, strength
increased for both groups (P = 0.0001) through 14 weeks of training, w
ith little improvement thereafter. Increases in muscle strength ranged
from 24-62% depending on the muscle group. Baseline plasma IGF-I conc
entrations were similar in both groups (mean +/- SEM, 106 +/- 9 mu g/L
), approximately half that observed in healthy young adults. In the rh
GH group, IGF-I levels increased to 255 +/- 32 mu g/L at week 15 and 2
18 +/- 21 mu g/L at week 24 (P < 0.001). In the placebo group, IGF-I i
ncreased slightly to 119 +/- 6 mu g/L at 24 weeks. IGF-binding protein
-a also increased in the rhGH group (P < 0.05). rhGH had no effect on
muscle strength at any time, and no systematic difference in muscle st
rength was observed between groups throughout the study. Body weight d
id not change in either group, but lean body mass increased, and fat m
ass decreased (P < 0.05) in the rhGH group. Supplementation with rhGH
does not augment the response to strength training in elderly men. The
se results suggest that deficits in GH secretion do not underlie the t
ime-dependent leveling off of muscle strength seen with training in th
e elderly and provide no support for the popular view of GH as an ergo
genic aid.