Twice-daily sessions result in a greater muscle strength and a similar muscle hypertrophy compared to once-daily session in resistance-trained men.

BACKGROUND The present study investigated the mid-term effects of training muscle groups once- versus twice-daily on morphofunctional adaptations in trained men. METHODS Participants were randomly assigned to 1 of 2 experimental groups: 1 daily session per muscle group (1S, n = 11), where every muscle group was trained once a day or 2 daily sessions per muscle group (2S, n = 12), where every muscle group was trained twice. Testing was conducted before intervention and after 8 weeks for maximal strength (1RM) and muscular endurance (60%1RM) for bench press and parallel back squat exercises, and muscle thickness (MT) of the biceps brachii, triceps brachii, vastus lateralis, anterior quadriceps and pectoralis major. RESULTS The major findings were as follows: (a) the increase in 1RM back squat was significantly greater in 2S (Δ=16.1%) compared to 1S (Δ=7.8%) (p<0.05) and (b) both groups significantly increased bench press 1RM (1S: Δ=4.6%; 2S: Δ=6.8%), back squat 60% 1RM (1S: Δ= 19.0%; 2S: Δ= 24.3%), bench press 60% 1RM (1S: Δ= 15.4%; 2S: Δ= 24.0%) and all MT outcomes (p< 0.05 for all), with no differences between experimental groups (1S and 2S). CONCLUSIONS This study provides evidence that a twice-daily resistance training augments lower-body muscular strength; however, the daily frequency does not seem to have any additive effect on upper-body muscular strength, muscular endurance, and muscle hypertrophy in trained men.