lean body mass, and increased strength over a
5-week period. However, this study has been
criticized on the grounds of poor experimental
design and statistical analysis. More recent
well-controlled studies (Fogelholm et al. 1993;
Lambertet al. 1993; Mitchell et al. 1993) with
experienced weightlifters or bodybuilders do not
support any ergogenic effect of various combina-
tions of arginine, ornithine and lysine on hGH
secretion, increased muscle mass, strength or
power.
Moreover, two well-controlled studies
revealed that hGH supplementation itself did
not increase muscle protein synthesis, muscle
size or strength in untrained males undergoing
a 12-week resistance-training programme
(Yarasheski et al. 1992) or muscle protein synthe-
sis or whole body protein breakdown in trained
weightlifters over a 2-week period (Yarasheski
et al. 1993).
safety
Although moderate doses of amino acid supple-
ments may be safe, larger doses, e.g. 170 mg
ornithine · kg–1body weight, may lead to gas-
trointestinal distress (osmotic diarrhoea). More-
over, the potential adverse health effects of
hGH administration are substantial, and most
researchers caution that the long-term health
risks of hGH administration, either genetically
358 nutrition and exercise
engineered or produced by amino acid supple-
mentation, are unknown (Bucci 1993).b-Hydroxy-b-methylbutyratetheory
b-Hydroxy-b-methylbutyrate is a metabolite
of the essential amino acid leucine, and is
currently being marketed as a dietary supple-
ment, calcium-HMB-monohydrate. Although its
metabolic role in humans is uncertain, HMB sup-
plementation is proposed to help exercisers max-
imize muscle gains during resistance training by
counteracting the catabolic effects of exercise-
induced stress on protein metabolism. Investiga-
tors hypothesize that HMB may be an essential
component of the cell membrane that is jeopar-
dized during exercise stress or that it may regu-
late enzymes important to muscle growth.efficacy
Animal studies involving poultry, cattle and pigs
have indicated that HMB supplementation may
increase lean muscle mass and decrease body fat.
(Nissenet al. 1994; Van Koevering et al. 1994).
However, HMB research with humans is very
limited and has emanated from a single labora-
tory. Collectively, three studies provide some
evidence supportive of an anabolic, or an anti-Fig. 26.1Some athletes consume
nutritional ergogenic aids in
attempts to increase serum levels
of anabolic hormones, with
resultant expected benefits of
increased muscle mass, strength
and power. Photo © Allsport /
Botterill.