Abstract
SUMMARY
Human skeletal muscle has a remarkable capability of adapting to a change in
demands. The preservation of this adaptability relies partly on a pool of resident myogenic stem cells (satellite cells, SCs). Extrinsic factors such as mechanical load (e.g. resistance exercise) and dietary protein constitute key factors in regulation of human skeletal muscle mass; however, the influence of divergent resistance exercise contraction modes and protein supplementation on SC content, is not well described. The overall aim of the present thesis was to investigate whether eccentric versus concentric resistance training and ingestion of protein influence myocellular adaptations, with special emphasis on muscle stem cell adaptations, during both acute and prolonged resistance exercise in human skeletal muscle.
Paper I. Whey protein supplementation accelerates satellite cell proliferation during
recovery from eccentric exercise
In paper I, we evaluated the effect of a single bout of unaccustomed eccentric exercise
on fiber type specific SC content by immunohistochemistry. Subjects received either hydrolysed whey protein (Whey) or iso-caloric carbohydrate (Placebo) in the days post eccentric exercise. Type II fiber-associated SCs/fiber increased at 24 and 48 hours in the Whey group, and was significantly different from Placebo at 48 hours. Similarly, in the Whey group, type II fiber-associated SCs/myonuclei was increased at 48 hours whereas the Placebo group only increased at 168 hours. In conclusion, protein supplementation may accelerate SC proliferation as part of regeneration or
remodeling processes after maximal eccentric exercise.
Paper II. Whey protein hydrolysate augments tendon and muscle hypertrophy independent of exercise contraction mode.
The aim of paper II was to investigate the effect of contraction mode specific
resistance training and protein supplementation on whole muscle and tendon hypertrophy. Quadriceps muscle and patellar tendon cross-sectional area (CSA) was quantified using magnetic resonance imaging pre and post 12 weeks of eccentric (Ecc) or concentric (Conc) resistance exercise combined with Whey or Placebo supplementation. Quadriceps CSA increased in both Whey and Placebo groups, with a greater increase in Whey compared to Placebo. Proximal patellar tendon CSA increased with Whey as well as with Placebo, with a tendency towards a greater increase in Whey compared to Placebo. Exercise contraction mode did not influence muscle or tendon hypertrophy. In conclusion, hydrolysed whey protein may augment both muscle and tendon hypertrophy independently of exercise contraction mode during training.
Paper III. Influence of exercise contraction mode and protein supplementation on human skeletal muscle satellite cell content and muscle cell growth.
The aim of paper III was to investigate the fiber type specific SC and myonuclei content, as well as myofiber CSA in response to the 12 weeks Ecc or Conc resistance exercise training combined with Whey or Placebo supplementation. Skeletal muscle biopsies were analysed for fiber-type specific SCs, myonuclei and myofiber CSA by immunohistochemistry. Following training, SC content increased with Conc, in both type I and type II fibers but not with Ecc. Type II fiber CSA increased exclusively with Whey-Conc, which was accompanied by a specific accretion of type II fiber myonuclei with Whey-Conc, but also with Placebo-Ecc. In conclusion, Conc constitutes a stronger driver of SC content than Ecc, whereas supplementation only exerted minor effects on SC content. In addition, type II myofiber hypertrophy is accentuated when combining
Conc resistance training with hydrolysed whey protein.
Paper IV. Effect of contraction mode specific resistance training and whey hydrolysate
supplementation on muscle residing stem cells.
The aim of paper IV was to investigate whether resistance training and protein
supplementation could modulate the muscle stem/stromal cell content, including alkaline phosphatase positive (ALP+) or neuron-glial antigen 2 positive (NG2+) pericytes. Pre and post 12 weeks of Ecc or Conc resistance training combined with Whey or Placebo supplementation, muscle biopsies were obtained and analysed for pericyte and SC content by immunohistochemistry. The number of ALP+ pericytes declined with Conc, while remaining unchanged with Ecc. NG2+ pericytes decreased with Conc as well as with Ecc. ALP+/SC ratio decreased exclusively with Conc.
Ingestion of whey protein did not influence stem cell content in muscle. In conclusion, both pericytes and SCs are responsive to resistance training and these changes may be more profoundly modulated with Conc compared to Ecc resistance training.
Human skeletal muscle has a remarkable capability of adapting to a change in
demands. The preservation of this adaptability relies partly on a pool of resident myogenic stem cells (satellite cells, SCs). Extrinsic factors such as mechanical load (e.g. resistance exercise) and dietary protein constitute key factors in regulation of human skeletal muscle mass; however, the influence of divergent resistance exercise contraction modes and protein supplementation on SC content, is not well described. The overall aim of the present thesis was to investigate whether eccentric versus concentric resistance training and ingestion of protein influence myocellular adaptations, with special emphasis on muscle stem cell adaptations, during both acute and prolonged resistance exercise in human skeletal muscle.
Paper I. Whey protein supplementation accelerates satellite cell proliferation during
recovery from eccentric exercise
In paper I, we evaluated the effect of a single bout of unaccustomed eccentric exercise
on fiber type specific SC content by immunohistochemistry. Subjects received either hydrolysed whey protein (Whey) or iso-caloric carbohydrate (Placebo) in the days post eccentric exercise. Type II fiber-associated SCs/fiber increased at 24 and 48 hours in the Whey group, and was significantly different from Placebo at 48 hours. Similarly, in the Whey group, type II fiber-associated SCs/myonuclei was increased at 48 hours whereas the Placebo group only increased at 168 hours. In conclusion, protein supplementation may accelerate SC proliferation as part of regeneration or
remodeling processes after maximal eccentric exercise.
Paper II. Whey protein hydrolysate augments tendon and muscle hypertrophy independent of exercise contraction mode.
The aim of paper II was to investigate the effect of contraction mode specific
resistance training and protein supplementation on whole muscle and tendon hypertrophy. Quadriceps muscle and patellar tendon cross-sectional area (CSA) was quantified using magnetic resonance imaging pre and post 12 weeks of eccentric (Ecc) or concentric (Conc) resistance exercise combined with Whey or Placebo supplementation. Quadriceps CSA increased in both Whey and Placebo groups, with a greater increase in Whey compared to Placebo. Proximal patellar tendon CSA increased with Whey as well as with Placebo, with a tendency towards a greater increase in Whey compared to Placebo. Exercise contraction mode did not influence muscle or tendon hypertrophy. In conclusion, hydrolysed whey protein may augment both muscle and tendon hypertrophy independently of exercise contraction mode during training.
Paper III. Influence of exercise contraction mode and protein supplementation on human skeletal muscle satellite cell content and muscle cell growth.
The aim of paper III was to investigate the fiber type specific SC and myonuclei content, as well as myofiber CSA in response to the 12 weeks Ecc or Conc resistance exercise training combined with Whey or Placebo supplementation. Skeletal muscle biopsies were analysed for fiber-type specific SCs, myonuclei and myofiber CSA by immunohistochemistry. Following training, SC content increased with Conc, in both type I and type II fibers but not with Ecc. Type II fiber CSA increased exclusively with Whey-Conc, which was accompanied by a specific accretion of type II fiber myonuclei with Whey-Conc, but also with Placebo-Ecc. In conclusion, Conc constitutes a stronger driver of SC content than Ecc, whereas supplementation only exerted minor effects on SC content. In addition, type II myofiber hypertrophy is accentuated when combining
Conc resistance training with hydrolysed whey protein.
Paper IV. Effect of contraction mode specific resistance training and whey hydrolysate
supplementation on muscle residing stem cells.
The aim of paper IV was to investigate whether resistance training and protein
supplementation could modulate the muscle stem/stromal cell content, including alkaline phosphatase positive (ALP+) or neuron-glial antigen 2 positive (NG2+) pericytes. Pre and post 12 weeks of Ecc or Conc resistance training combined with Whey or Placebo supplementation, muscle biopsies were obtained and analysed for pericyte and SC content by immunohistochemistry. The number of ALP+ pericytes declined with Conc, while remaining unchanged with Ecc. NG2+ pericytes decreased with Conc as well as with Ecc. ALP+/SC ratio decreased exclusively with Conc.
Ingestion of whey protein did not influence stem cell content in muscle. In conclusion, both pericytes and SCs are responsive to resistance training and these changes may be more profoundly modulated with Conc compared to Ecc resistance training.
| Original language | English |
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| Publication status | Published - 2014 |
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