Table 4.

Effect of repeated use of supplements on sports-related performance protocol

Study	Subjects and designa	Supplement protocol	Performance protocol	Enhancement of performance	Summary
Caffeine
Stadheim et al. [51]	Elite junior cross-country skiers (n = 8 M)	3 or 4.5 mg/kg caffeine dose @ 75 min pre event	Cross-country skiing  2 × 10 min x-country skiing TT, separated by 24 h	Event 1: Yes at both doses Event 2: Yes at both doses	Poling distance during the 10-min time-trial was improved with both caffeine doses on day 1 compared with the placebo trial: 4.0 [±3.3] % and 4.0 [±2.9] % for 3 mg and 4.5 mg doses, respectively. Despite greater muscular pain and increased creatine kinase levels on day 2 after caffeine use, performance was improved by 5.0 [±3.6] % and 5.1 [±2.8] %
Beetroot juice/nitrate
Hoon et al. [57]	Highly-trained cyclists (n = 26 M) Crossover design	70-ml (4 mmol nitrate) BJ concentrate @ 2.5 h pre TT1 or @ 2.5 h pre TT2 or 70 ml BJ @ 2.5 pre TT1 + 35 ml BJ top up straight after TT1	Cycling  2 × 4 min cycling TT separated by 75 min (simulation of team pursuit schedule at London Olympic Games)	Event 1: Perhaps Event 2: Potential impairment	Sophisticated mixed model analysis took into account caliber of cyclist and learning/order effect, while identifying 1% improvement as the smallest worthwhile change. Overall, nitrate treatment (acknowledged as a suboptimal dose in light of more recent evidence) was associated with a small but unclear improvement of 1.3 ± 1.7% in the first time trial, but also a potentially unclear impairment of performance in the second time trial, perhaps due to the carryover of additional fatigue [−0.3 ± 1.6%]
Bicarbonate
Joyce et al. [58]	Highly-trained swimmers (n = 8 M) Crossover design	Serial bicarbonate protocol: 3 days @ 300 mg/kg/day sodium bicarbonate divided in 3 daily doses + final dose on day 4 Performance protocol undertaken on days 4 and 5	Swimming  2 × 200 m TT separated by 24 h to simulate swimming competition	Event 1: No Event 2: No	Plasma bicarbonate concentration was increased after 3 days’ serial loading, although to a smaller extent than when same daily amount was taken as acute dose 90 min before the TT. However bicarbonate concentrations returned to baseline 24 h after last dose. There was no enhancement of TT performance immediately after serial loading compared with placebo trial (1:58.53 ± 0:05.64 vs. 1:59.02 ± 0:05.82 and no difference in between this TT and a further TT after 24 h. Mild symptoms of gut discomfort were noted but not different to those noted in acute loading protocol
Carr et al. [37]	Club level rowers (n = 4 M, 3 F) Crossover design	Serial bicarbonate protocol: 3 days @ 500 mg/kg/day sodium bicarbonate split into five doses Performance protocol undertaken on days 2 and 4	Rowing  2 × 2000 m TT separated by 48 h to simulate regatta	Event 1: No Event 2: No	Despite the increase in blood bicarbonate, serial bicarbonate supplementation failed to enhance performance in terms of 2000 m mean power, stroke rate or RPE, or characteristics over each 500-m segment. The authors suggest that the lower caliber of rower in this study may explain the small effect size of performance changes. The reliability of performance in response to chronic supplementation protocol was high; suggesting that individual variability in responsiveness can be quickly established from a trial

BJ beetroot juice, M male, F female, RPE rating of perceived exertion, TT time trial

^aRandomized, double-blind, placebo-controlled unless noted