Yohimbine Ingestion Mitigates Morning-Associated Decrements in High-Intensity Exercise Performance

Exercise performance tends to suffer during the morning compared to the evening, which may decrease potential training adaptations. Currently, it is unclear how nutritional interventions may affect this phenomenon and whether supplementation may allow for the attainment of optimal performance regardless of the time of day. The purpose of this study was to investigate the effects of acute yohimbine ingestion on morning-associated decrements in performance and psychophysiological responses to exercise. Physically active females (n = 16) were recruited to participate in three total visits, each with a different treatment: (1) placebo-morning (PL-AM), (2) yohimbine-morning (YHM-AM; oral 2.5 mg), and (3) placebo-afternoon (PM). The morning and afternoon visits occurred between 7:00–8:00 h and 16:00–17:00 h, respectively. The experimental treatments in the morning were ingested 20 min prior to capillary blood collection, which was completed pre- and post-exercise. Following a warm-up, participants completed a 2000 m time trial on a rowing ergometer. Power output, heart rate (HR), and rating of perceived exertion (RPE) were recorded every minute. Time to competition (TTC) and subjective energy, focus, and alertness were documented post-exercise. Pre- and post-exercise blood lactate (La) and plasma hypoxanthine (HX) levels were also assessed. The trials were separated by a 48 h washout period. The results showed that power output (p = 0.010) was lower and TTC (p = 0.003) was significantly slower with PL-AM compared to PM. Furthermore, YHM-AM resulted in higher power output (p = 0.035) and faster TTC (p = 0.007) compared to PL-AM, with no differences compared to PM (p > 0.05). Post-exercise La was significantly lower with YHM-AM compared to PL-AM (p = 0.046) and PM (p = 0.001). Pre-exercise plasma HX, as measured via conversion to xanthine, was significantly higher with PM (p = 0.039), while the levels trended higher with YHM-AM (p = 0.060) compared to PL-AM. Subjective energy was higher with YHM-AM (p = 0.045) and PM (p = 0.009) compared to PL-AM, while alertness was only higher for YHM-AM compared to PL-AM (p = 0.045). No statistical differences between the treatments were found for RPE or HR (p > 0.05). These findings indicate that YHM ingestion attenuates performance decrements in the morning. Improvements in performance may be underpinned by improved feelings of energy and alterations in metabolism. Practically, YHM may represent an effective ergogenic aid to combat a lack of energy and low performance during the morning.