A recent study by the University of Birmingham published in the magazine Current Biology observed that athletic performance can have a 26% variation in the course of the day. The study concerned 20 hockey players and it evaluated cardiovascular resistance during various moments of the day, from 7:00 a.m. to 10:00 p.m. The results showed that the best athletic performance time is late afternoon but, as in most studies, this result expresses  the mean value. Instead, if we consider the single subjects in the group, noteworthy differences appeared: the subjects who were used to waking up and getting up early in the morning gave a better response at around 12:00. On the contrary, others who got up with difficulty and late gave better results in the evening and, finally, there were intermediate subjects who expressed a better performance at around 3:00 p.m. A reassessment of scientific literature by Tunisian scientists (Chortle Strength and Conditioning Research 2012) actually shows that both performance and strength are correlated with body temperature, which reaches its maximum peak  between 4:00 p.m. and 6:00 p.m. It is also very interesting to observe, as it appears in the study “Relationship between time of day and variations in blood pressure response to aerobic exercise” (A. Di Blasio et al. Med Sport 2010 University Center of Sport Medicine Chieti Italy), that the time in which physical activity is performed also involves certain health-linked parameters such as artery pressure. This study monitored pressure response during physical aerobic exercise and in the following 30 minutes, in three different moments of the day (9:30 a.m.-2:00 p.m.-6:30 p.m.). The results showed a different trend in  diastolic pressure response (minimum pressure) during the test, while there was a higher decrease in recovery when this was performed at 6:30 p.m. The sensation of strain was higher in the morning. In conclusion: performing physical exercise in late afternoon seemed to optimize the hypotensive effect induced by  exercise on diastolic arterial pressure. In a study carried out on speed runners, Bill Kraemer of the University of Connecticut showed that melatonin levels (the sleep hormone which can persist in the morning and can cause sleepiness) were higher in the morning than in the afternoon and this coincided with a lower performance during race, whereas high jump was not influenced by melatonin levels. I believe that other hormones, besides melatonin, are involved in athletic performance and this is in conformity with the beliefs of Chronomorphotherapy. If we refer to the study reported in the magazine Current Biology, I believe that most of the female hockey players had a hyperlipogenetic morphology, that is, they were robust athletes with a predisposition for violent sports. This corresponds to a prevalence of the adrenal glands as dominant glands with higher cortisol and adrenalin production. In this type of subjects intense physical activity causes excessive adrenal glands  stimulation with a cortisol peak which is normally already high in the morning. This hypercortisolemia has a negative effect on athletic performance both because cortisol acts negatively at the level of cognitive systems and because it has  a catabolic effect at muscular level. In the morning, as soon as they wake up, these subjects are extremely tired and start to get their acts together only late in the morning, performing better towards the evening. This is the typical condition of executives, dominant hyper-adrenergic subjects who, not by chance, rarely reach their office before 10 in the morning, but who stay on until late in the evening. On the contrary, the typical secretary type who is hypolipolytic would be in the office early in the morning and would therefore work overtime. Hypolipolytic subjects are already efficient early in the morning, whereas the “intermediate” types of the Birmingham study are more efficient at around midday, when their dominant gland, the thyroid, works at its best. However, there are other reasons why athletic performance in the morning can be hindered. It is commonly believed that the biological clock influences muscular strength, above all regulating energy production at cell level, which is higher in late afternoon. However, there is a system, unconsciously used by most of us, which alters the biological clock and can drastically increase our athletic performance:  caffeine! Caffeine has an ergogenic effect in that it increases cellular energy,  inhibiting cyclic AMP disaggregation which leads to glycogenolysis and to lipolysis with energy production. Caffeine also improves the absorption of calcium at the level of muscular cells and this allows  the interaction between actin and myosin, necessary for muscular contraction. Caffeine, without doubt, also has a well-known stimulating effect on our central nervous system which predisposes us to  higher mental concentration. In order to verify the promising power of caffeine to improve athletic performance in the morning, Rodriguez et al. tested twelve trained men while performing squat and horizontal bench extension exercise at 75% of maximum weight, in different moments of the day, with and without caffeine, in a placebo double blind experiment (that is, none of the athletes and the experimenters knew who was taking caffeine and who the placebo).  The result was that the group who trained in the afternoon without caffeine was significantly stronger than the morning group who was given the placebo, thus confirming the negative impact of morning training on the performance. When both groups received caffeine, there were no significant differences both in squat and bench extension activity. This showed that caffeine can annul the  “gap” in performance between morning and afternoon. Caffeine can trigger the biological clock, activating the AMPK enzyme, an energy regulator at cellular level which, in turn, activates SIRT 1, an enzyme which is normally activated by low levels of energy  (for example in low calorie diets) and which accelerates energy production starting from fats and glucose. SIRT 1 can regulate the biological clock, inhibiting the CLOCK protein which represents the central biological clock rhythmically activated according to circadian rhythm. Since CLOCK protein is activated when energy consumption is low  and it improves energy accumulation at cellular level and not its production, this explains why in the morning, on awakening (since energy consumption is still low after  rest)  the effect of CLOCK protein, which decreases energy production, is responsible for the minor muscular performance which is due to a drop in energy availability for muscular contraction.   In conclusion, the power of caffeine to stimulate SIRT 1, which inhibits the CLOCK protein, promotes a better biological clock for morning training. This also suggests that other integrators which activate SIRT 1, possibly in association with caffeine, such as for example resveratrol, could have an even higher effect on the biological clock, conditioning and improving athletic performance in the morning.