To increase strength and build muscle, most people will visit the gym three or four days per week, training once each day, and many don't even consider the concept of twice-per-day training. While twice-a-day training can make you feel more lethargic, impact your recovery between sessions and make you weaker if done incorrectly, it can lead to new strength and muscle gains if done properly and has certain benefits over training just once per day.
The History of Twice-a-Day Training
Twice-a-day training was popularized by the weightlifters of the former Soviet bloc countries during the 1970s, and one of the most famous proponents of this method was Ivan Abadjiev -- creator of the Bulgarian Weightlifting System. His athletes would train two, three or even four times per day, often doing the same exercises in each session, but the focus of the workouts was always performing quality reps, and rarely failing lifts.
Better Workout Quality
If you train once per day for an hour, by the time you're 40 minutes into your session, you can often feel tired, run down and eager to leave the gym. According to strength coach Christian Thibaudeau, training twice per day allows you to perform shorter workouts, which means you suffer less fatigue in each session, don't get bored and perform at a higher level in each workout, which leads to better muscular and neurological adaptations.
Priming the Nervous System
Performing low-rep, explosive exercises with heavy weights in the morning fires up your muscular motor units and central nervous system, which leaves you primed to perform lighter, higher-rep, muscle-building exercises in the evening, says Nick Mitchell, head trainer at Ultimate Performance Gym in London. It also increases your work capacity, meaning that you can do more training in less time, which leads to muscular strength and endurance gains.
While training twice per day can be effective, it can also be easy to burn out on it if you aren't careful. Charles Poliquin, owner of the Poliquin Performance Center for elite athletes, advises training for no longer than 40 minutes in each session and splitting your training into three five-day cycles. In the first two five-day cycles, train twice per day, then deload in the third cycle and train with lighter weights only once per day. You may also wish to employ recovery methods such as sports massages and ice baths, and ensure an adequate intake of calories, protein, carbohydrates and fats.