Aging is often associated with a reduction in one’s ability to exercise. A common causative factor is age-related deterioration, known as sarcopenia, and changes in viable skeletal muscle . It has been previously shown that there is a direct relationship between sarcopenia onset and depleted systemic carnosine [2–5]. Carnosine is a dipeptide synthesized by carnosine synthetase in the presence of β-Alanine and L-Histidine [4, 6–10] predominantly found within skeletal muscle. It functions to improve myofiber contractility via enhancing sarcomere sensitivity to calcium, as well as to maintain pH homeostasis [4, 6, 8, 10–15]. By acting as a pH buffer, carnosine allows for larger accumulation of lactate during exercise by delaying the associated acidification of systemic pH known to have negative effects on exercise performance and cognition [2, 6, 12]. As carnosine concentrations become depleted as a result of sarcopenia, its ability to buffer pH becomes limited manifesting a quicker onset of acidosis [2, 3].
Systemic carnosine levels have been successfully elevated by supplementing β-Alanine, a non-essential amino acid and rate limiting factor in carnosine synthesis [8, 16], at 3.2 g/day and 6.4 g/day [10, 17]. Additionally, β-Alanine induced increases in systemic carnosine are sustained over a range of 4 months following supplementation . Studies have been investigated β-Alanine supplementation in young adults in an effort to increase exercise performance via multiple dosing strategies and exercise modalities. Hill et al.  showed that increasing the dose of β-Alanine from 4.0 g/day to 6.4 g/day over 4 weeks improves total work done by high intensity, college aged cyclists. Multiple other studies have also found similar results with varying dosage strategies. For example, Hoffman et al  found that 6.0 g of β-Alanine for 28 days improved tactical performance and jumping ability, but not serial subtraction test time in soldiers. 6.4 g/day was found to improve upper-body Wingate bouts .
The improvements in exercise capacity seen in young adults led to investigation involving β-Alanine supplementation in aging adults to combat symptoms of sarcopenia [2, 4]. Studies of aging populations have used a variety of dosage schemes such as 1.6 g/day, 2.4 g/day and 3.2 g/day for a range of 28 to 84 days [2–4]. Despite the positive results seen in younger populations, only del Favero et al.  has directly tested muscle carnosine or endurance cycling ability in aging subjects. They found an 85.4% increase in gastrocnemius carnosine levels as well as improved endurance exercise capacity following 12 weeks of 3.2 g/day of β-Alanine supplementation . Different variations of dosages and length of supplementation within aging populations have, however, shown significant increases in cycling ability without directly measuring intramuscular carnosine levels [3, 4].
Furthermore, exercise has shown to affect executive functioning, such as decision making and short term memory . Interestingly, researchers have shown that carnosine also accumulates in the central nervous system, specifically the cerebral cortex [13, 14]. In cerebral tissue, carnosine acts as an anti-oxidant with neuro-protective properties [7, 9, 13, 20]. Hoffman et al.  used rats to show that 30 day β-Alanine supplementation increases carnosine concentrations in the cerebral cortex, hippocampus, amygdala, hypothalamus and thalamus when exposed to stress. In humans, however, a 28 day β-Alanine supplementation showed improved physical fitness performance in military personnel, yet provided only minor improvements in decision making and reaction time . Further, a recently published study was also unable to demonstrate improved executive function when testing at time points immediately prior to and following exercise .
The present study was undertaken to further investigate the effect of β-Alanine supplementation on exercise endurance and executive function in a middle aged human population. Our primary outcome was exercise performance measured as time-to-exhaustion (TTE). Our secondary outcome was Stroop Test derived indices of executive function. We hypothesize that β-Alanine supplementation would (a) improve exercise performance and (b) attenuate the decline in post exercise executive function.