|It may come as a surprise, but for the chronic, endurance enhancing effects of green tea supplements caffeine obviously isn't necessary. It appears, though, as if the effects were mediated solely by increases in fat oxidation.|
Now that you know the main outcomes of the study and hand, it's about time to take a look at how the scientists arrived at the conclusion that "a 4 week dGTE intervention favourably enhanced substrate utilisation and subsequent performance indices, but did not alter TFA concentrations in comparison to PL" (Roberts. 2015).
The scientists recruited fourteen, recreationally active men (mean ± SE; age = 21.4 ± 0.3 yrs; weight = 76.37 ± 1.73 kg; body fat = 16.84 ± 0.97%, peak oxygen consumption [VO_ 2peak] = 3.00 ± 0.10 L·min−1) who participated in a study with a standardized double-blind, placebo-controlled, parallel design intervention. More specifically, the participants were randomly assigned to consume either
- 517mg/day of capsulated decaffeinated green tea extract (delivering 70% or 400 mg EGCG which is equivalent to 6–7 cups of green tea per day | dGTE group) or
- 517mg/day of an identically looking placebo supplement (PLA group)
over the complete 4 week study duration. This makes the study a chronic supplementation study which may partly explain that it did not require caffeine, an acute phase ergogenic, to see significant increases in exercise performance.
"Following body composition and resting cardiovascular measures, participants cycled for 1 hour at 50% VO_ 2peak, followed by a 40 minute performance trial at week 0, 2 and 4. Fat and carbohydrate oxidation was assessed via indirect calorimetry. Pre-post exercise blood samples were collected for determination of total fatty acids (TFA). Distance covered (km) and average power output (W) were assessed as exercise performance criteria" (Roberts. 2015).In addition to the three testing sessions, all subects participated in three regular 60min steady-state cardio sessions at only 50% of their maximal VO2 (that's walking for almost everyone, expect the obese). Now, obviously, the previously highlighted total distance the subjects covered during the 40 minute performance trial increased in both groups (Figure 1, left). In the dGTE group, however, these changes were significantly more pronounced than in the placebo group.
|Figure 1: Total distance covered during the 40 minute performance trial (left) and substrate utilization (right) before and after the intervention in the placebo and dGTE groups (Roberts. 2015).|
|Figure 2: Changes in body composition and heart rate over the 4-week study period (Roberts. 2015).|
- Roberts, Justin D., et al. "The effect of a decaffeinated green tea extract formula on fat oxidation, body composition and exercise performance." Journal of the International Society of Sports Nutrition 12.1 (2015): 1.