In their study, Yeo and colleagues determined the effects of a cycle training program in which selected sessions were performed with low muscle glycogen content on training capacity and subsequent endurance performance, whole body substrate oxidation during submaximal exercise, and several mitochondrial enzymes and signaling proteins with putative roles in promoting training adaptation.
Now, the interesting thing about Yeo's study and the reason I want to discuss their results first is that the scientists from the School of Medical Sciences at the RMIT University in Victoria, Australia used trained subjects - seven endurance-trained cyclists/triathletes who were used to training daily anyway. During the three week study period, however, the subjects had to stick to one of the following training schedules:
- Daily training (Daily - aka "High") - In this group the subjects alternated between 100-min steady-state aerobic rides (AT) one day, followed by a high-intensity interval training session (HIT; 8x5 min at maximum self-selected effort) the next day.
- Twice every second day training (Two-A-Day - aka "Low") - Subject who had been randomly assigned to this group performed the AT, first, then 1–2 h later, the HIT.
|Figure 1: Markers of fact glycogen use and fat oxidation during steady state exercise after 3 weeks of training (Yeo. 2008)|
Want to learn more? At this point you may be reminded of a previous article of mine with the telling title "8x Increase in "Mitochondria Building" Protein PGC1-Alpha W/ Medium Intensity Exercise in Glycogen Depleted Elite(!) Cyclists: Training Revolution or Recipe for Disaster?". If not, I suggest you head back and read it now!The obvious question that's probably preying on your minds already is: How on earth does that relate to strength training, bro? Well, let's see... so, in the strength training study by Hansen, et al., the authors actually speculated to observe an effect as it was observed in the study I discuss in the article I referenced in the red box, i.e. that "training at a low muscle glycogen content [during a second workout on the same day] would enhance training adaptation" (Hansen. 2005). Therefore, the Hansen et al performed a study in which seven healthy untrained men performed knee extensor exercises with one leg trained in a two-a-day fashion (2h rest between the 1h sessions), the other one in everyday. Luckily, the study duration in this study was 10 and not just 3 weeks.
Against that background it is not surprising that the training load increased significantly. Since the latter has little to do with the mitochondria, it is also not that surprising that the increase in maximal workload was identical for the two legs. What may be surprising for those who think that training twice a day would be bogus, however, is that the time until exhaustion and total volume during the post-test was "markedly more increased" in the leg that was trained twice a day, albeit only every other day vs. the one that was trained daily, but only once (see Figure 3).
|Figure 3: Relative performance increases from pre- to post-test (left) and glycogen levels before and after exhausting bouts of knee extensor exercises (right) | high = daily training, low = twice a day, but only every other day (Hansen. 2005).|
- Hansen, Anne K., et al. "Skeletal muscle adaptation: training twice every second day vs. training once daily." Journal of Applied Physiology 98.1 (2005): 93-99.
- Yeo, Wee Kian, et al. "Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens." Journal of Applied Physiology 105.5 (2008): 1462-1470.