The students had exactly the same time schedule at the university from sunrise to sunset under the control of the experimental team. Participants had taken part in various recreational low-intensity physical activities such us walking, jogging, or aerobics in our university.
The participants were prescribed with standard isocaloric meals to consume, with breakfast at 07:30 h, lunch at 12:00 h, and dinner at 20:00 h. Only water was allowed ad libitum between meals. They were requested to maintain their habitual physical activity throughout the experimental period and to avoid strenuous activity before each test session. The overall daily energy intake goal was set at 10.5 MJ (2500 kcal) per capita/day.
|Figure 1: Caffeine affects both body temperature and physical performance during sleep deprivation (Souissi. 2014)|
"Participants were selected according to their usual consumption of caffeine and on the basis of their answers to the Horne and Ösberg Self-Assessment Questionnaire (Horne. 1979) (i.e., to have a group without “extreme type” (i.e., participants were selected as “neither type”)). This second criterion resulted in a sample of participants who shared the same timing in terms of rising times (06:30 ± 00:30 h) and bedtimes (23:00 ± 00:30 h). Participants reported no sleep disorder, are non-smokers, and do not consume caffeine or any alcoholic beverages."After four consecutive nights of sleep in the laboratory (sleep adaptation: between 22:30 and 07:00 h), in a randomized order, participants performed four test sessions: after placebo or 5 mg/kg of caffeine ingestion during a baseline night (RN) or a night of 36 h of total sleep deprivation (TSD).
|Does this look remotely familiar? If it does, you are already "tolerant".|
"The study documented tolerance development to the subjective effects of caffeine: after chronic dosing, administration of caffeine produced significant subjective effects in the chronic placebo group but not in the chronic caffeine group." The study also provided indirect evidence for tolerance development: during chronic dosing, the chronic caffeine and placebo groups did not differ meaningfully on ratings of mood and subjective effect. That's important, because it means that not all benefits are lost; plus, it explains why you still don't quit drinking your coffee ;-)
|Figure 2: Caffeine boosts cognitive performance during sleep deprivation (Souissi. 2014)|
- the reaction time,
- the squat jump (SJ), and
- the Wingate tests at 18:00 h with 15 min of recovery in-between
|Figure 3: Results of the profile of mood test w/ & w/out caffeine before and after TSD (Souissi. 2014)|
- Evans, Suzette M., and Roland R. Griffiths. "Caffeine tolerance and choice in humans." Psychopharmacology 108.1-2 (1992): 51-59.
- Horne, John A., and Olov Ostberg. "A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms." International journal of chronobiology 4.2 (1976): 97.
- Souissi, Makram et al."The effects of caffeine ingestion on the reaction time and short-term maximal performance after 36h of sleep deprivation." Physiology & Behavior 131 (2014): 1-6.