|Study offers yet another, different look at AM vs. PM and AM/PM cardio.|
Well, to elucidate said relation, the scientists conducted three 24-h indirect calorimetry sessions in the course of which their subjects performed 100 min of exercise before breakfast (AM), after lunch (PM) or two sessions of 50 min exercise before breakfast and after lunch (AM/PM).
For almost three days, the scientists from the University of Tsukuba had their subjects, well-trained endurance athletes, live in a metabolic chamber, where they slept for 7-h from 23:00 to 6:00, and three meals (breakfast at 8:30, lunch at 12:30 and supper at 18:00) were provided.
"Subjects were instructed to remain awake and to keep sedentary position other than prescribed exercise session and bedtime by the protocol. On day 2, subjects performed a session of 100 min exercise beginning at 6:30 (AM), at 16:00 (PM) or two sessions of 50 min exercise at 6:30 and at 16:00 (AM/PM) at 65% of V ． O2max using a treadmill (T1201, Johnson Health Tech Japan, Tokyo, Japan). In addition to 100 min running, subjects were instructed to perform 15 min of warm-up activity twice a day (6:15 and 15:45). Subjects were allowed to leave the chamber for 30 min to take a shower (22:00 - 22:30)" (Iwayama. 2015).On day 3, subjects followed the same protocol of day 2 except from the exercise session, and exited the chamber at 16:00. Twenty-four-hour energy expenditure and nutrients oxidation calculated from 6:00 of day 2 to 6:00 of day 3 were compared among the three experimental conditions. Experimental meals were designed to achieve individual energy balance assuming resting metabolic rate to be 24.0 kcal/kg/day, and physical activity factor to be 1.75 (2464 ± 75 kcal/day) in day 1, 2.48 (3544 ± 127 kcal/day) in day 2 and 1.75 in day 3 (1587 ± 47 kcal for breakfast and lunch), according to the estimated energy requirement for Japanese (MHLW. 2003).
|Figure 1: Macronutrient intake (g) during the three days in the metabolic chamber (Iwayama. 2014)|
"All subjects completed 3 trials, and there were no significant differences in body mass, body fat and fat free mass among the trials. During exercise, energy expenditure was similar, but oxidation of fat and carbohydrate were different among the trials (P kleiner 0.01). Fat oxidation during exercise in descending order were exercise performed before breakfast (AM: 481 ± 41), two split sessions before breakfast and after lunch (AM/PM: 279 ± 22) and after lunch (PM: 131 ± 5 kcal/100min). Conversely, carbohydrate oxidation during exercise in descending order were PM (1189 ± 45), AM/PM (992 ± 50) and AM (815 ± 52 kcal/100min) (see Figure 2)" (Iwayama. 2015).The results also revealed that the accumulated 24-h energy expenditure was similar among the trials (AM: 3540 ± 124, AM/PM: 3525 ± 128, PM: 3487 ± 120 kcal/24-h, P=0.15). Since it was balanced with energy intake, the energy balance over 24-h was zero (AM: +4 ± 74, AM/PM: +19 ± 60, PM: +58 ± 60 kcal/24-h, P=0.15):
Figure 2: Energy balance (top) and fat oxidation (bottom).
- Contrary, accumulated 24-h carbohydrate oxidation in descending order were PM (2558 ± 110), AM/PM (2374 ± 114) and AM (2062 ± 96 kcal/24-h) (P < 0.01).
- Urinary nitrogen excretion was not significantly different among the 3 trials (AM: 13.1 ± 1.2, AM/PM: 13.3 ± 1.5, PM: 12.5 ± 1.3 g/day, P=0.39).
|Reread the AM-Cardio study here.|
|Figure 4: The impact of AM cardio on metabolism and energy intake in the study at hand.|
Energy debt = fat oxidation up = total energy balance down = potential fat loss?
In the words of a non-mathematician this means that the more fat you oxidize, the more your total energy expenditure will suffer. In contrast, the nadir of relative carbohydrate balance was negatively correlated with 24-h fat oxidation (r = -0.40, P < 0.05), this is not a surprise (remember: your body has to choose what it wants to burn, carbs or fats).
|Figure 4: Association between fat oxidation and average energy balance and nadir of energy balance (Iwayama. 2015).|
|Re-read the results of Aragon's and Schoenfeld's morning cardio study w/ untrained subjects here.|
What remains to be seen, though is if doing cardion in the AM can, by increasing the fat oxidation and thus reducing the reliance on carbs eventually help people to eat less compared to those who do their training after lunch.
The results of a 2005 study by Maraki, et al. (2005) would suggest otherwise. In their study, Maraki et al. were able to show that doing a standardized, albeit shorter workout in the AM did not have different effects on appetite than the same workout in the PM. If that's in fact the case, it's eventually not surprising that Schoenfeld et al. have not found a weight loss advantage for AM cardio in their recent study | Comment on Facebook!