Protein Supplementation Does Not Further Increase Latissimus Dorsi Muscle Fiber Hypertrophy after Eight Weeks of Resistance Training in Novice Subjects, but Partially Counteracts the Fast-to-Slow Muscle Fiber Transition.
The response to resistance training and protein supplementation in the latissimus dorsi muscle (LDM) has never been investigated. We investigated the effects of resistance training (RT) and protein supplementation on muscle mass, strength, and fiber characteristics of the LDM. Eighteen healthy young subjects were randomly assigned to a progressive eight-week RT program with a normal protein diet (NP) or high protein diet (HP) (NP 0.85 vs. HP 1.8 g of protein·kg(-1)·day(-1)). One repetition maximum tests, magnetic resonance imaging for cross-sectional muscle area (CSA), body composition, and single muscle fibers mechanical and phenotype characteristics were measured. RT induced a significant gain in strength (+17%, p < 0.0001), whole muscle CSA (p = 0.024), and single muscle fibers CSA (p < 0.05) of LDM in all subjects. Fiber isometric force increased in proportion to CSA (+22%, p < 0.005) and thus no change in specific tension occurred. A significant transition from 2X to 2A myosin expression was induced by training. The protein supplementation showed no significant effects on all measured outcomes except for a smaller reduction of 2X myosin expression. Our results suggest that in LDM protein supplementation does not further enhance RT-induced muscle fiber hypertrophy nor influence mechanic muscle fiber characteristics but partially counteracts the fast-to-slow fiber shift.
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. antonio.paoli@unipd.it.
Antonio
A
Paoli
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. francesco.pacelli@unipd.it.
Quirico F
QF
Pacelli
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. linacancellara@gmail.com.
Pasqua
P
Cancellara
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. luana.toniolo@unipd.it.
Luana
L
Toniolo
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. tatiana.moro.phd@gmail.com.
Tatiana
T
Moro
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. marta.canato@unipd.it.
Marta
M
Canato
Salvatore Maugeri Foundation, Pavia 27100, Italy. danilo.miotti@fsm.it.
Danilo
D
Miotti
AIFeM (Italian Medicine and Fitness Federation), Ravenna 48121, Italy. neri@cervia.com.
Marco
M
Neri
Euganea Medica, Diagnostic Centre, Via Colombo 13, Albignasego (Padova) 35020, Italy. aldo.morra@euganeamedica.it.
Aldo
A
Morra
Euganea Medica, Diagnostic Centre, Via Colombo 13, Albignasego (Padova) 35020, Italy. marco.quadrelli@euganeamedica.it.
Marco
M
Quadrelli
Department of Biomedical Sciences, University of Padova, Padova 35131, Italy. carlo.reggiani@unipd.it.
Carlo
C
Reggiani
D000328:Adult; D001823:Body Composition; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage*; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000502:physiology; D055070:Resistance Training; D064171:Superficial Back Muscles / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
D004044:Dietary Proteins
myosin isoform; nutrition; single muscle fiber mechanics; strength training; supplementation; whey protein