The present study showed that 4-week consumption of both 75 g/d whole almonds and isocaloric cookies during the winter training season improved cycling distance of time trial and elements of exercise performance relative to BL, with a greater change in the ALM, even though BL’s performance was likely partially affected by relatively high ambient temperature and humidity.
The data suggests that a few notable nutrients/compounds abundant in almonds might improve the effectiveness of the training in a synergistic way via modulating CHO reservation/utilization (by improving glucose transport into skeletal muscle and glycogen synthesis [36, 37]), antioxidant capacity [6, 7], oxygen transportation/utilization and metabolism regulation [19–26] through slightly raised arginine, insulin, and NO, and statistically increased VE, TAOC and Hb level (Table 2) without greatly affecting fluid balance (Table 3).
In general, training elevates fat-derived energy contribution to an endurance competition . A continuous supply of fatty acids is crucial to athletes participating in distance/endurance competition at moderate intensity, whereas CHO serves as the main fuel during an intense exercise, especially during sprint of a competition [36, 39]. Thus, CHO preloading and loading prior to or during a race are essential strategies for athletes participating in an endurance competition . Statistically, our study showed that there were no differences in VO2, CHO and fat oxidation during TT between COK and ALM. However ALM had lower VO2 and higher CHO oxidation and lower fat oxidation than BL while ALM did not change HR and EE as compared to BL (Figure 3). It should be noted that ALM (not COK) had lower oxygen consumption during TT (Figure 3), lower blood FFA and higher blood glucose at the end of exercise than BL (Figure 5, Table 2), suggesting almonds might help athletes to mobilize more previously reserved CHO, instead of breaking down fat as an energy source during training and the intense exercise . A higher Hb level in ALM might also help athletes transport more oxygen to skeletal muscles during exercise.
L-arginine, the natural precursor of NO, may stimulate insulin secretion , decrease oxygen consumption [23, 25] and ammonia liberation  during exercise and regulate vascular dilation [43, 44]. A clinical trial showed that a combined arginine and antioxidant supplement improved exercise performance in the elderly . Insulin facilitates glucose transfer to skeletal muscle tissues and subsequent glycogen synthesis [42, 45, 46]. Our results suggest that almond consumption may contribute to an improvement in cycling performance- related elements via the effect of arginine on insulin secretion and muscle glycogen synthesis without enhancing insulin sensitivity via down-regulated insulin levels noted in patients with diabetes [14, 47, 48]. Unsatisfactorily, we did not observe a statistical difference in blood arginine and NO (Table 2) because daily arginine intake from almonds (about 2 g excluding that from the diet) provided ~100 mg/kg BM which was less than that administered in other’s studies [25, 27]; athletes had a larger need and utilization (metabolism) of arginine due to intensive exercise; there was a large inter-individual variation; arginine may work with other almond nutrients in a synergistic or additive manner.
Several studies had shown that quercetin alone or plus antioxidants improved mitochondrial biogenesis, VO2max, and exercise capacity [19–22]. Therefore, the effect of quercetin on mitochondrial biogenesis and oxygen consumption might also be linked to almond consumption in this study.
Human studies demonstrated that almond consumption increases circulating α-tocopherol concentration in a dose-dependent manner [4, 12], decreases biomarkers of oxidative stress in smokers and hypercholesterlemic patients [1, 49]. Phenolics in almonds have shown to exert antioxidant action against reactive radicals in humans [6, 7]. Thus, a diverse array of phenolic and polyphenolic compounds in almonds might contribute to improving antioxidant capacity in the athletes. Even though ALM (not COK) had a higher blood VE than BL and higher TAOC than COK, we did not find other significant changes related to the antioxidant effects of almond consumption in trained athletes. It is worth noting that the antioxidant effect by almonds was not a predominant factor in improving the elements associated with endurance performance in trained athletes due to their good adaptation to intensive training. Further, one of benefits exerted by almonds might be attributed to decreased inflammation markers (not determined in the study) .