Gymnastik- och idrottshögskolan, GIH

The muscular and myocellular adaptations to low-load resistance exercise training (LL-RET) remain incompletely understood in the trained state. The primary aim of this study was to examine adaptations to an LL-RET regimen, comparing these to a high-load training regimen (HL-RET). Fourteen resistance-trained males and females (26.4 ± 4.4 years) participated in a 9-week RET program (twice per week). Using a within-subject design, each individual trained one leg with HL-RET (3-5 repetitions), and the other with LL-RET (20-25 repetitions), all sets performed to volitional failure. Maximal strength (1 RM) and muscle thickness were assessed. Muscle biopsies were analyzed for fiber type composition, fiber cross-sectional area (fCSA), and satellite cell- and myonuclear content using immunofluorescence. The training regimens led to comparable increases in 1 RM in multi-joint movements (21 ± 10%), but not in single-joint movements where HL-RET was superior (9 ± 13% vs -3 ± 10%). Regardless of training regimen, muscle thickness increased pre- to post-intervention by 7 ± 17% at the mid-thigh site and 8 ± 8% at the distal site. However, this was not accompanied by changes at the myocellular level, with no observed differences in fCSA and fiber type composition. Satellite cell content increased by 25 ± 57% in type I fibers, independent of training regimen, but no changes were noted in myonuclear content. LL-RET can replicate many aspects of HL-RET leading to similar increases in muscle hypertrophy and strength. Our study supports the notion that comparable adaptations to RET can be achieved using widely distinct loading regimens.

Muscle disuse has rapid and debilitating effects on muscle mass and overall health, making it an important issue from both scientific and clinical perspectives. However, the myocellular adaptations to muscle disuse are not yet fully understood, particularly those related to the myonuclear permanence hypothesis. Therefore, in this study, we assessed fiber size, number of myonuclei, satellite cells, and capillaries in human gastrocnemius muscle after a period of immobilization following an Achilles tendon rupture. Six physically active patients (5M/1F, 43 {plus minus} 15 years) were recruited to participate after sustaining an acute unilateral Achilles tendon rupture. Muscle biopsies were obtained from the lateral part of the gastrocnemius before and after six weeks of immobilization using a plaster cast and orthosis. Muscle fiber characteristics were analyzed in tissue cross-sections and isolated single fibers using immunofluorescence and high-resolution microscopy. Immobilization did not change muscle fiber type composition nor cross-sectional area of type I or type II fibers, but muscle fiber volume tended to decline by 13% (p=0.077). After immobilization, the volume per myonucleus was significantly reduced by 20% (p=0.008). Myonuclei were not lost in response to immobilization but tended to increase in single fibers and type II fibers. No significant changes were observed for satellite cells or capillaries. Myonuclei were not lost in the gastrocnemius muscle after a prolonged period of immobilization, which may provide support to the myonuclear permanence hypothesis in human muscle. Capillaries remained stable throughout the immobilization period, whereas the response was variable for satellite cells, particularly in type II fibers.

Detailed skating velocity profiles of high-calibre ice hockey players are lacking, and an increasing number of ice hockey players are using dynamic skating blade holders, but the impact of these skates on performance remains unclear. This study aims to compare velocity profiles between dynamic and fixed blade holders across various skating techniques. Twenty high-calibre skaters from one of the three highest-ranked leagues in Sweden (age 19.7 ± 4.1 years, body mass 77.9 ± 7.6 kg) completed three maximal trials involving linear forward sprints, forward c-cuts, and backward c-cuts on two separate occasions using two different types of blade holders. Split times were recorded at 5 m intervals from 5–40 m and average velocity was calculated for each distance segment. Velocity increased every 5 m up to 40 m, independent of the blade holder type across all techniques. No significant differences in performance were observed for linear forward sprinting or forward c-cuts between the blade holder types. However, backward c-cuts showed a significant improvement in speed with the dynamic holders at several intervals: 0–5 m (2.42 m/s vs. 2.38 m/s, p = 0.048), 15–20 m (5.86 m/s vs. 5.76 m/s, p = 0.009), and 35–40 m (6.84 m/s vs. 6.67 m/s, p = 0.021), resulting in 1-2% faster split times. The results indicate that high-calibre skaters progressively increase their velocity up to 40 m in both forward and backward skating, without reaching maximal velocity. Additionally, dynamic blade holders may offer a performance advantage during backward skating, making them a valuable option for players who frequently utilise this technique in competitive play.

This study investigates how different recovery periods after high-intensity interval training (HIIT) affects strength and explosive performance during a power training (PT) session. Fifteen female elite ice hockey players (22.5 ± 5.2 years) performed PT, including 6 sets of 2 repetitions (reps) of isometric leg press (ILP) and 6 sets of 3 reps of countermovement jump (CMJ), following a rested state and 10 minutes, 6 hours, or 24 hours after HIIT (3 sets of 8 × 20 seconds at 115% of power output at maximal oxygen consumption on a cycle ergometer). Peak force (PF) and peak rate of force development (pRFD) were measured during the ILP. Peak jump height (PJH), concentric phase duration (ConDur), eccentric phase duration, total duration, peak power (PP), velocity at peak power (V@PP), and force at peak power were measured during CMJ. The following variables were significantly reduced when only a 10-minute recovery period was allowed between HIIT and PT: PF was reduced by 7% (p < 0.001), pRFD by 17% (p < 0.001), PJH by 4% (p < 0.001), ConDur by 4% (p = 0.018), PP by 2% (p = 0.016), and V@PP by 2% (p = 0.007). None of the measured variables were reduced when PT was performed 6 and 24 hours after HIIT. We conclude that strength and explosive performance of elite female ice hockey players is reduced 10 minutes after HIIT but not negatively affected if a rest period of at least 6 hours is provided between HIIT and PT.

The objective of this work was to investigate myonuclear permanence and transcriptional regulation as mechanisms for cellular muscle memory after strength training in humans. Twelve untrained men and women performed 10 weeks of unilateral elbow-flexor strength training followed by 16 weeks of de-training. Thereafter, 10 weeks' re-training was conducted with both arms: the previously trained arm and the contralateral untrained control arm. Muscle biopsies were taken from the trained arm before and after both training periods and from the control arm before and after re-training. Muscle biopsies were analysed for fibre cross-sectional area (fCSA), myonuclei and global transcriptomics (RNA sequencing). During the first training period, myonuclei increased in type 1 (13 ± 17%) and type 2 (33 ± 23%) fibres together with a 30 ± 43% non-significant increase in mixed fibre fCSA (P = 0.069). Following de-training, fCSA decreased in both fibre types, whereas myonuclei were maintained, resulting in 33% higher myonuclear number in previously trained vs. control muscle in type 2 fibres. Furthermore, in the previously trained muscle, three differentially expressed genes (DEGs; EGR1, MYL5 and COL1A1) were observed. Following re-training, the previously trained muscle showed larger type 2 fCSA compared to the control (P = 0.035). However, delta change in type 2 fCSA was not different between muscles. Gene expression was more dramatically changed in the control arm (1338 DEGs) than in the previously trained arm (822 DEGs). The sustained higher number of myonuclei in the previously trained muscle confirms myonuclear accretion and permanence in humans. Nevertheless, because of the unclear effect on the subsequent hypertrophy with re-training, the physiological benefit remains to be determined. KEY POINTS: Muscle memory is a cellular mechanism that describes the capacity of skeletal muscle fibres to respond differently to training stimuli if the stimuli have been previously encountered. This study overcomes past methodological limitations related to the choice of muscles and analytical procedures. We show that myonuclear number is increased after strength training and maintained during de-training. Increased myonuclear number and differentially expressed genes related to muscle performance and development in the previously trained muscle did not translate into a clearly superior responses during re-training. Because of the unclear effect on the subsequent hypertrophy and muscle strength gain with re-training, the physiological benefit remains to be determined.

Kombinerad styrke- och konditionsträning är vardagsmat för elitidrottare och elitmotionärer. Men personer som tränar mycket är särskilt känsliga för den här träningsformen. Passens ordningsföljd och rätt mängd vila är därför viktigt för att maximera styrkeutvecklingen, visar ny forskning.

Isometric leg press (ILP) and countermovement jump (CMJ) are commonly used to obtain strength- and power-related variables with important implications for health maintenance and sports performance. To enable the identification of true changes in performance with these measurements, the reliability must be known. This study evaluates the between-session reliability of strength- and power-related measures obtained from ILP and CMJ. Thirteen female elite ice hockey players (21.5 ± 5.1 years; 66.3 ± 8.0 kg) performed three maximal ILPs and CMJs on two different occasions. Variables from the ILP (peak force and peak rate of force development) and CMJ (peak power, peak force, peak velocity, and peak jump height) were obtained. The results were reported using the best trial, an average of the two best trials, or an average of three trials. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were high (ICC > 0.97; CV < 5.2%) for all outcomes. The CV for the CMJ (1.5-3.2%) was lower than that for the ILP (3.4-5.2%). There were no differences between reporting the best trial, an average of the two best trials, or an average of the three trials for the outcomes. ILP and CMJ are highly reliable when examining strength- and power-related variables in elite female ice hockey players.

This study aimed to investigate the effect of intrasession exercise order of maximal effort flywheel resistance training (RT; 436 repetitions [rep]) and high-intensity interval training (HIIT, 2–438 rep of 20 second at 130% of Watt atV̇O2max [wV̇O2max]), on the development of maximal strength and power in elite team-sport athletes. A 7-week training intervention involving 2 training sessions per week of either HIIT followed by RT (HIIT + RT, n 5 8), RT followed by HIIT (RT + HIIT, n 5 8), or RTalone (RT, n 5 7) was conducted in 23 elite male bandy players (24.7 6 4.3 years). Power and work were continuously measured during the flywheel RT. Isometric squat strength (ISq), countermovement jump, squat jump, and V̇O2max were measured before and after the training period. Power output during training differed between the groups (p 5 0.013, h2p5 0.365) with RT producing more power than HIIT + RT (p 5 0.005). ISq improved following RT + HIIT (;80%, d 5 2.10, p 5 0.001) and following HIIT + RT(;40%, d 5 1.64, p 5 0.005), and RT alone (;70%, d 5 1.67, p 5 0.004). V̇O2max increased following RT + HIIT and HIIT + RT(;10%, d51.98, p50.001 resp. d52.08, p50.001). HIIT before RT reduced power output during RT in elite team-sport athletes but did not lead to blunted development of maximal strength or power after a 7-week training period. During longer training periods(.7-weeks), it may be advantageous to schedule RT before HIIT because the negative effect of HIIT + RT on training quality increased during the final weeks of training. In addition, the largest training effect on maximal strength was observed following RT +HIIT.

PURPOSE: This study compared the effects of heavy resisted sprint training (RST) versus unresisted sprint training (UST) on sprint performance among adolescent soccer players.

METHODS: Twenty-four male soccer players (age: 15.7 [0.5] y; body height: 175.7 [9.4] cm; body mass: 62.5 [9.2] kg) were randomly assigned to the RST group (n = 8), the UST group (n = 10), or the control group (n = 6). The UST group performed 8 × 20 m unresisted sprints twice weekly for 4 weeks, whereas the RST group performed 5 × 20-m heavy resisted sprints with a resistance set to maximize the horizontal power output. The control group performed only ordinary soccer training and match play. Magnitude-based decision and linear regression were used to analyze the data.

RESULTS: The RST group improved sprint performances with moderate to large effect sizes (0.76-1.41) across all distances, both within and between groups (>92% beneficial effect likelihood). Conversely, there were no clear improvements in the UST and control groups. The RST evoked the largest improvements over short distances (6%-8%) and was strongly associated with increased maximum horizontal force capacities (r = .9). Players with a preintervention deficit in force capacity appeared to benefit the most from RST.

CONCLUSIONS: Four weeks of heavy RST led to superior improvements in short-sprint performance compared with UST among adolescent soccer players. Heavy RST, using a load individually selected to maximize horizontal power, is therefore highly recommended as a method to improve sprint acceleration in youth athletes.