PurposeIrisin is a recently identified exercise-induced hormone that increases energy expenditure, at least in rodents. The main purpose of this study was to test the hypothesis that Irisin increases acutely in blood after singular sessions of intense endurance exercise (END) and heavy strength training (STR). Secondary, we wanted to explore the relationship between body composition and exercise-induced effects on irisin, and the effect of END and STR on muscular expression of the irisin gene FNDC5.MethodsNine moderately trained healthy subjects performed three test days using a randomized and standardized crossover design: one day with 60 minutes of END, one day with 60 minutes of STR, and one day without exercise (CON). Venous blood was sampled over a period of 24h on the exercise days.ResultsBoth END and STR led to transient increases in irisin concentrations in blood, peaking immediately after END and one hour after STR, before gradually returning to baseline. Irisin responses to STR, but not END, showed a consistently strong negative correlation with proportions of lean body mass. Neither END nor STR affected expression of FNDC5, measured 4h after training sessions, though both protocols led to pronounced increases in PGC-1α expression, which is involved in transcriptional control of FNDC5.ConclusionThe results strongly suggest that single sessions of intense endurance exercise and heavy strength training lead to transient increases in irisin concentrations in blood. This was not accompanied by increased FNDC5 expression, measured 4h post-exercise. The results suggest that irisin responses to resistance exercise are higher in individuals with lower proportions of lean body mass.

Limited data exist on the efficacy of low-load blood flow-restricted strength training (BFR), as compared directly to heavy-load strength training (HST). Here, we show that 12 wk of twice-a-week unilateral BFR [30% of one repetition maximum (1RM) to exhaustion] and HST (6-10RM) of knee extensors provide similar increases in 1RM knee extension and cross-sectional area of distal parts of musculus quadriceps femoris in nine untrained women (age 22 ± 1 yr). The two protocols resulted in similar acute increases in serum levels of human growth hormone. On the cellular level, 12 wk of BFR and HST resulted in similar shifts in muscle fiber composition in musculus vastus lateralis, evident as increased MyHC2A proportions and decreased MyHC2X proportions. They also resulted in similar changes of the expression of 29 genes involved in skeletal muscle function, measured both in a rested state following 12 wk of training and subsequent to singular training sessions. Training had no effect on myonuclei proportions. Of particular interest, 1) gross adaptations to BFR and HST were greater in individuals with higher proportions of type 2 fibers, 2) both BFR and HST resulted in approximately four-fold increases in the expression of the novel exercise-responsive gene Syndecan-4, and 3) BFR provided lesser hypertrophy than HST in the proximal half of musculus quadriceps femoris and also in CSApeak, potentially being a consequence of pressure from the tourniquet utilized to achieve blood flow restriction. In conclusion, BFR and HST of knee extensors resulted in similar adaptations in functional, physiological, and cell biological parameters in untrained women.

The purpose of this study was to compare the effects of 10 weeks of effort-matched short intervals (SI; n = 9) or long intervals (LI; n = 7) in cyclists. The high-intensity interval sessions (HIT) were performed twice a week interspersed with low-intensity training. There were no differences between groups at pretest. There were no differences between groups in total volume of both HIT and low-intensity training. The SI group achieved a larger relative improvement in VO(2max) than the LI group (8.7% ± 5.0% vs 2.6% ± 5.2%), respectively, P ≤ 0.05). Mean effect size (ES) of the relative improvement in all measured parameters, including performance measured as mean power output during 30-s all-out, 5-min all-out, and 40-min all-out tests revealed a moderate-to-large effect of SI training vs LI training (ES range was 0.86-1.54). These results suggest that the present SI protocol induces superior training adaptations on both the high-power region and lower power region of cyclists' power profile compared with the present LI protocol.

This file was dowloaded from the institutional repository Brage NIH -brage.bibsys.no/nih Ellefsen, S., Vikmoen, O., Slettaløkken, G., Whist, J. E., Nygård, H., Hollan, I.... Rønnestad, B. (2014). Irisin and FNDC5: effects of 12-week strength training, and relations to muscle phenotype and body mass composition in untrained women. MethodsEighteen untrained women performed 12 weeks of progressive whole body heavy strength training, with measurement of strength, body composition, expression of irisin-related genes (FNDC5 and PGC1α) in two different skeletal muscles, and levels of serum-irisin and -thyroid hormones, before and after the training intervention. ResultsThe strength training intervention did not result in changes in serum-irisin or muscle FNDC5 expression, despite considerable effects on strength, lean body mass (LBM) and skeletal muscle phenotype. However, our data indicate that training affects irisin biology in a LBM-dependent

Determination of muscle fiber composition in human skeletal muscle biopsies is often performed using immunohistochemistry, a method that tends to be both time consuming, technically challenging, and complicated by limited availability of tissue. Here, we introduce quantitative reverse transcriptase polymerase chain reaction (qRT-PCR)-based Gene-family profiling (GeneFam) of myosin heavy chain (MyHC) mRNA expression as a high-throughput, sensitive, and reliable alternative. We show that GeneFam and immunohistochemistry result in similar disclosures of alterations in muscle fiber composition in biopsies from musculus vastus lateralis and musculus biceps brachii of previously untrained young women after 12 weeks of progressive strength training. The adaptations were evident as (a) consistent increases in MyHC2A abundance; (b) consistent decreases in MyHC2X abundance; and (c) consistently stable MyHC1 abundance, and were not found using traditional reference gene-based qRT-PCR analyses. Furthermore, muscle fiber composition found using each of the two approaches was correlated with each other (r = 0.50, 0.74, and 0.78 for MyHC1, A, and X, respectively), suggesting that GeneFam may be suitable for ranking of individual muscle phenotype, particularly for MyHC2 fibers. In summary, GeneFam of MyHC mRNA resulted in reliable assessment of alterations in muscle fiber composition in skeletal muscle of previously untrained women after 12 weeks of strength training.