Data from this study suggest that ninety days of BA supplementation may increase physical working capacity in elderly men and women. These findings may be clinically significant, as a decrease in functional capacity to perform daily living tasks has been associated with an increase in mortality [18
], primarily due to increased risk of falls [9
]. Further, deVries et al. [13
] and Alexander et al. [8
] have suggested that falls may be related to fatigue-induced deterioration of motor coordination. Thus, an improved resistance to fatigue, as reported in this study, (Figure and ) may be important to consider when working with a similar population.
The concept of physical working capacity (PWC), a measure of aerobic power, muscular endurance and efficiency is typically measured by oxygen consumption rate (VO2
) during a maximal graded exercise test (GXT) [19
]. Recently, several studies have reported on the effects of BA supplementation on PWCFT
during incremental cycle ergometry tests in young men and women [16
]. Stout et al. [16
] reported that 28 days of BA supplementation in a younger population (21–27 years) resulted in a significant increase in PWCFT
by 12 – 15%, respectively. In agreement, the current study demonstrated a 28.5% increase in PWCFT
after ninety days of BA supplementation. The two-fold increase in PWCFT
in the elderly compared to young men and women in previous studies may be due to differences in initial skeletal muscle carnosine levels or supplementing duration. In support, Tallon et al. [4
] reported that in Type II skeletal muscle, carnosine concentration was 47% lower in elderly (70.4 ± 5.0 yrs) compared to younger (23.8 ± 4.6 yrs) men and women, although Kim [20
] found normal muscle carnosine levels in elderly Korean subjects with impaired glucose tolerance. Harris et al. [2
] demonstrated that 28 days of BA supplementation significantly (60%) increased skeletal muscle carnosine levels while Hill et al. [15
] demonstrated a further 20% increase when BA supplementation was continued for an additional 35 days. In light of these reports, the greater change in PWCFT
in elderly participants in the present study, compared to previous studies in young men and women, was most likely due to both initial carnosine levels and length of time of BA supplementation.
De Vries et al. [13
] suggested the PWCFT
test may be more appropriate and sensitive to training effects on PWC in elderly, compared to other methods (i.e. VO2 max
) that require maximal effort and may be ill-advised or possibly hazardous in this population. To our knowledge, this is the first study to examine the effects of BA supplementation using the PWCFT
test in elderly men and women. However, de Vries et al. [13
] did examine the effects of 10 weeks of moderate intensity (70% PWCFT
) endurance training three times per week on PWCFT
in elderly men and women (67.9 ± 5.3 years). The results showed a significant (p < 0.05), 30% increase in PWCFT
as a result of the endurance training. While the results by de Vries et al. [13
] support and recommend endurance training as a means to significantly improve physical working capacity, it should be noted that the elderly subjects in the current study were untrained, and the 28.5% increase in PWCFT
occurred without any type of additional training during the ninety days of supplementation.
It has been proposed that exercise-induced decreases in intramuscular pH may interfere with the excitation-contraction coupling process of skeletal muscle, which, in turn may lead to decreases in power output and fatigue [21
]. Maintaining the intracellular pH during exercise could therefore be important for normal muscle function in the elderly [4
]. In order to maintain pH homeostasis, various buffering systems are involved, including active H+
export from muscle [2
]. However, the immediate line of defense remains the buffering of H+
by intracellular physico-chemical buffers, principally phosphates and carnosine. Marsh et al. [22
] demonstrated that there was a significant delay in the onset of intracellular acidosis during progressive exercise after six weeks of moderate intensity training, resulting in an increased capacity for submaximal work in a similar cohort of elderly individuals. Improving the ability to buffer intramuscular H+
accumulation, therefore, appears to be an important factor for delaying the onset of fatigue and increasing exercise capacity in older men and women.
Based on these results, it is not unreasonable to expect that introducing BA supplementation to increase muscle carnosine levels, prior to starting an exercise program in elderly men and women, would lead to an improvement in the quality of training. This would be especially true if muscle carnosine contents were already reduced with elderly persons. The limiting factor for muscle carnosine synthesis is the availability of BA, obtained either from uracil degradation in the liver or from the release of BA from the ingestion of carnosine (and related dipeptides in meat) [2
]. From preliminary observations showing that the level of carnosine is reduced by up to 50% in vegetarian subjects [23
], compared to age matched controls, it seems likely that the capacity of the body to produce BA is limited and capable of supporting only a limited capacity to synthesize carnosine. This is overcome in meat eaters through the dietary supply of BA. However, elderly subjects, maintained on a diet with a restricted meat intake would be expected to show a similar reduction in their muscle carnosine content as vegetarians, and to respond beneficially to BA supplementation.