If you structure twice-a-day training correctly, there is no down side to this superior method for increasing strength and power. It will easily translate to increased training outcomes and greater performance in your sport.
A new study in the European Journal of Applied Physiology compared the effect of twice-a-day training on a variety of strength and power parameters in recreational trainees and elite weightlifters. The twice-a-day training consisted of the same workout separated by a six-hour rest. Participants performed ten singles with two minutes rest between repetitions of the front squat using a load of 90 percent of the 1RM for both training sessions.
The weightlifters demonstrated a significantly greater ability to generate and sustain peak force during both training sessions than the recreational trainees. Peak force varied by 26 to 38 percent greater for the weightlifters than the recreational group across repetitions.
The weightlifters had an insignificant decline in ability to generate peak force from the first to last repetition in the first training session, whereas the recreational group had a substantial 20 percent drop in peak force from the first to last rep of the first training session.
Most interesting: The weightlifters began the second training session by producing greater peak force than at any time point during the first session, and they had an insignificant decline in peak force by the final rep of the second session. The recreational group had a significant drop in peak force generation for all lifts in the second session.
Researchers suggest double-day training is so effective because it will increase neuromuscular function and lead to greater motor unit synchronization so that the nervous system is able to co-activate numerous muscle groups to produce force quickly over and over.
To get the most out of twice-a-day training, you need to ease into it with short workout sessions so that your body is able to adapt. Start with 20 minute workouts that are spaced four to six hours apart. Work up to 40 to 60 minute workouts—longer will be counterproductive.
Working heavy in the morning, with higher reps at night is quite effective. Do sets of 4 to 6 reps in the morning, and sets of 12 to 15 at night. If you are more interested in strength development, your morning workouts would be more in the 1 to 3 rep range, while your evening workouts would max out at eight reps.
Another option is to train the same body part twice on the same day. For example, train multi-joint movements in the morning (incline presses and dips for the upper body) and single-joint lifts in the afternoon (flys and other isolation exercises).