Human Single Muscle Fiber Hypertrophy And Myonuclear Domain After Time Restricted Eating And Resistance Exercise

Time restricted eating (TRE) involves limiting meals to specific blocks of time (e.g., 16 h fasting, 8 h eating). This diet has been shown to decrease body fat and overall body mass due to caloric deficit. However, little is known regarding the effects of TRE in a caloric surplus on single muscle fiber (SMF) hypertrophy and myonuclear domain (MND) when combined with resistance exercise (RE) in humans. PURPOSE: To determine the effects of TRE and RE training on SMF size and MND in human longitudinal SMF imaged in 3D via laser scanning confocal microscopy (LSCM). METHODS: Previously resistance trained healthy adults (6 males, 6 females) underwent an 8-week RE training program on a TRE (16:8 h fasting:eating) or control (CON) diet (continuous eating) with equal protein and caloric load per bodyweight and sex (10% caloric surplus). Participants underwent pre- and post-RE training vastus lateralis (VL) muscle biopsies. SMF were manually isolated, processed, imaged (LSCM), and analyzed. Mean differences were investigated by time (pre-RE vs post-RE) and group (TRE vs CON) via ANOVA (significance set at p ≤ 0.05; data presented as mean ± standard deviation). RESULTS: Both TRE (n = 6, 109 SMF) and CON (n = 6, 110 SMF) groups had significant increases in SMF size after RE training (p = 0.018; η2 = 0.446), with no differences between groups [SMF volume (μm3): TRE pre-RE: 558256 ± 203075, post-RE: 804245 ± 227039; CON pre-RE: 745139 ± 143380, post-RE: 863112 ± 251804]. While large interindividual variability existed among participant’s fiber size, SMF volume increased in 10 of 12 individuals after RE training. However, MND did not significantly change following RE in either group [MND volume (μm3): TRE pre-RE: 7102 ± 1727, post-RE: 8543 ± 1430; CON pre-RE: 9077 ± 2999, post-RE: 8715 ± 2136]. CONCLUSION: Both TRE and CON diets can illicit muscle hypertrophy when paired with 8-weeks of RE training in trained healthy adults. While myonuclei and satellite cells are likely involved in regulating this growth, MND size did not differ after 8-weeks of RE training in either group. This data suggests that people considering either TRE or CON diets, coupled with RE training, can expect similar SMF growth if protein content and caloric surplus are maintained. Supported by: CSUBIOTECH New Investigator Grant (to JRB)