Type II muscle fibre properties are not associated with balance recovery following large perturbations during walking in young and older adults

Falls among older adults are often attributed to declining muscle strength with ageing. Associations between muscle strength and balance control have been reported, but the evidence for, and key mechanisms of resistance exercise in fall prevention are unclear. No studies have directly examined the relationship between muscle fibre characteristics and reactive balance control. Here, we address whether or not Type II muscle fibre characteristics associate with reactive balance during walking in young and older adults with varying muscle fibre type composition. We analyse muscle biopsy-derived fibre characteristics and stability during a treadmill-based walking perturbation (trip-like) task of healthy young adults, healthy, normally active older adults, trained older adults and physically impaired older adults. We find no significant associations between Type II muscle fibre properties and reactive balance during walking, indicating that practitioners and researchers should consider more than just the muscle tissue properties when assessing and intervening on fall risk.

Effect of aerobic exercise on muscle structure and expression of proteins promoting hypertrophy and metabolism in aged rats

Aging and physical inactivity lead to histochemical changes in muscles. The expression of many muscle proteins, including brain-derived neurotrophic factor (BDNF), silent information regulator of transcription 1 (SIRT1), and peroxisome proliferator-activated receptor γγ coactivator-1α (PGC-1a), declines with age. However, the effect of aerobic exercise on muscle structure and the expression profile of these proteins in elderly rats is unknown. Here, we investigated whether short-term aerobic exercise improves muscle structure and increases BDNF, SIRT1, and PGC-1a levels in aged rats. Ten male Wistar rats (95-week-old) were assigned to sedentary (SED) or exercise (Ex) groups. The Ex group performed running on a treadmill for 1 h, 6 times per week, for 2 weeks. The extensor digitorum longus muscles were removed to examine the muscle fibre type composition, cross-sectional area, and capillary-to-fibre (C/F) ratio. BDNF, SIRT1, and PGC-1a levels were evaluated by western blotting. Relative to the SED group, the Ex group showed increased proportion of Type I fibres (P<0.05), cross-sectional area of all muscle fibre types (P<0.05), succinate dehydrogenase activity (P<0.001), C/F ratio (P<0.05), and expression of BDNF, SIRT1, and PGC-1a (P<0.05).Thus, 2 weeks of aerobic exercise is sufficient to improve muscle histology and hypertrophic marker protein expression, indicating that it could prevent skeletal muscle atrophy in elderly rats.

Muscle Fibre Types and Their Relation to Meat Quality Traits in Pigs

The authors have been studying various characteristics of muscle fibres and their relationship to the meat quality parameters for many years. However, the conclusions drawn by researchers often differ. A higher proportion of glycolytic IIB fibres in pig muscles is usually related to paler meat with lower water holding capacity. On the other hand the relationship between muscle fibres and meat texture parameters is not clear. Studies using immunohistochemistry methods that allow a more detailed classification of individual muscle fibre types could bring new findings in this area. It would thus be possible to influence muscle fibre type composition in the muscle to achieve the desired meat quality using various extrinsic and intrinsic factors. The main aim of this review is to summarise current knowledge on the description of muscle fibres typology and the effect of their morphological traits on pork meat quality.

PL-016 Endurance training, muscle fibre type composition and the maximal capacity for fat oxidation

Objective A greater capacity for fat oxidation in endurance trained athletes is linked to greater utilisation of intramuscular lipid (IMCL). IMCL breakdown occurs only in type I muscle fibres yet little is known about the fibre type specific abundance of lipid regulatory proteins. We explored the impact of endurance training on the maximal rate fat oxidation, muscle fibre type and muscle fibre type specific abundance of proteins regulating IMCL metabolism. Methods Endurance trained (n=7, 28 ± 3 years, VO2max62.6 ± 1.6 ml·min-1·kg-1) and untrained (n=8, 25 ± 1 years, VO2max44.9 ± 1.9 ml·min-1·kg-1) males performed an incremental exercise test to determine maximal fat oxidation rate. Muscle fibre type composition and fibre type-specific IMCL content was assessed with immunofluorescence microscopy and protein abundance was analysed with immunoblotting on pooled single muscle fibres and whole muscle. Results Endurance trained individuals displayed a higher peak fat oxidation rate (0.49 ± 0.05 vs. 0.20 ± 0.03 g·min-1, P<0.05), which correlated with type I fibre percentage (R = 0.83, P < 0.01) and VO2max (R = 0.78, P < 0.01). Type I muscle fibres from endurance trained individuals had a greater abundance of ATGL. In whole muscle, the endurance trained group had greater abundance of PLIN2, PLIN5 and ATGL compared to the untrained group (P < 0.05). Furthermore, autophagy flux measured as LC3-II/I ratio was higher in type I muscle fibres and LC3-II/I, lysosomal markers (LAMP2) and chaperone-mediated autophagy markers (LAMP2A) were all higher in whole muscle of endurance trained individuals (P < 0.05). Conclusions These results demonstrate that the maximal rate of fat oxidation is related to the proportion of type I muscle fibres. Furthermore, IMCL storage and the abundance of key proteins regulating lipid metabolism is fibre type specific and greater in endurance trained individuals. Muscle fibre type composition should be considered when investigating the regulation of IMCL utilisation and markers of autophagy.

Acute upregulation of PGC-1α mRNA correlates with training-induced increases in SDH activity in human skeletal muscle

The purpose of the present study was to determine if acute responses in PGC-1α, VEGFA, SDHA, and GPD1–2 mRNA expression predict their associated chronic skeletal muscle molecular (SDH–GPD activity and substrate storage) and morphological (fibre-type composition and capillary density) adaptations following training. Skeletal muscle biopsies were collected from 14 recreationally active men (age: 22.0 ± 2.4 years) before (PRE) and 3 h after (3HR) the completion of an acute bout of sprint interval training (SIT) (eight 20-s intervals at ∼170% peak oxygen uptake work rate separated by 10 s of recovery). Participants then completed 6 weeks of SIT 4 times per week with additional biopsies after 2 (MID) and 6 (POST) weeks of training. Acute increases in PGC-1α mRNA strongly predicted increases in SDH activity (a marker of oxidative capacity) from PRE and MID to POST (PRE–POST: r = 0.81, r2 = 0.65, p < 0.01; MID–POST: r = 0.79, r2 = 0.62, p < 0.01) and glycogen content from MID to POST (r = 0.60, r2 = 0.36, p < 0.05). No other significant relationships were found between acute responses in PGC-1α, VEGFA, SDHA, and GPD1–2 mRNA expression and chronic adaptations to training. These results suggest that acute upregulation of PGC-1α mRNA relates to the magnitude of subsequent training-induced increases in oxidative capacity, but not other molecular and morphological chronic skeletal muscle adaptations. Additionally, acute mRNA responses in PGC-1α correlated with VEGFA, but not SDHA, suggesting a coordinated upregulation between PGC-1α and only some of its proposed targets in human skeletal muscle.