Journal of Sport and Health Science最新文献

Background: Residual force enhancement (rFE), defined as increased isometric force following active lengthening compared to a fixed-end isometric contraction at the same muscle length and level of activation, is present across all scales of muscle. While rFE is always present at the cellular level, often rFE "non-responders" are observed during joint-level voluntary contractions.

Methods: We compared rFE between the joint level and single fiber level (vastus lateralis biopsies) in 16 young males. In vivo voluntary knee-extensor rFE was measured by comparing steady-state isometric torque between a stretch-hold (maximal activation at 150°, stretch to 70°, hold) and a fixed-end isometric contraction, with ultrasonographic recording of vastus lateralis fascicle length (FL). Fixed-end contractions were performed at 67.5°, 70.0°, 72.5°, and 75.0°; the joint angle that most closely matched FL of the stretch-hold contraction's isometric steady-state was used to calculate rFE. The starting and ending FLs of the stretch-hold contraction were expressed as % optimal FL, determined via torque-angle relationship.

Results: In single fiber experiments, the starting and ending fiber lengths were matched relative to optimal length determined from in vivo testing, yielding an average sarcomere excursion of ∼2.2-3.4µm. There was a greater magnitude of rFE at the single fiber (∼20%) than joint level (∼5%) (p = 0.004), with "non-responders" only observed at the joint level.

Conclusion: By comparing rFE across scales within the same participants, we show the development of the rFE non-responder phenomenon is upstream of rFE's cellular mechanisms, with rFE only lost rather than gained when scaling from single fibers to the joint level.

Background: Fat loss mainly conveys the benefits of caloric restriction for people living with type 2 diabetes. The literature is equivocal regarding whether exercise facilitates fat loss during caloric restriction. This analysis aimed to assess the dose-response effects of exercise in combination with a caloric restriction on fat mass (FM) and FM percentage (FM %) in persons with diagnosed type 2 diabetes.

Methods: In this secondary analysis of a 4-armed randomized trial, 82 persons living with type 2 diabetes were randomly allocated to the control group (CON) (n = 21), diet control (DCON) (25 % caloric restriction; n = 20), diet control and exercise 3 times per wk (MED) (n = 20), or diet control and exercise 6 times per wk (HED) (n = 21) for 16 wk. The primary analysis was the change in FM% points. Secondary analyses included fat-free mass and visceral adipose tissue (VAT) volume (cm³).

Results: FM% decreased compared to CON by a mean difference of -3.5% (95% confidence interval (95%CI): -5.6% to -1.4%), -6.3% (95%CI: -8.4% to -4.1%), and -8.0% (95%CI: -10.2% to -5.8%) for DCON, MED, and HED, respectively. Compared to DCON, MED and HED decreased FM% by -2.8% (95%CI: -4.9% to -0.7%) and -4.5% (95%CI: -6.6% to -2.4%), respectively. The difference in FM% between HED and MED was -1.8% (95%CI: -3.9% to 0.4%). DCON and MED decreased fat-free mass compared to CON, whereas HED preserved fat-free mass (-0.2% (95%CI: -2.0% to 1.7%)). Compared to CON, VAT volume decreased by -666.0 cm³ (95%CI: -912.8 cm³ to -385.1 cm³), -1264.0 (95%CI: -1679.6 cm³ to -655.9 cm³), and -1786.4 cm³ (95%CI: -2264.6 cm³ to -1321.2 cm³) more for DCON, MED, and HED, respectively. HED decreased VAT volume more than DCON (-1120.4 cm³ (95%CI: -1746.6 cm³ to -639.4 cm³)) while the remaining comparisons did not reveal any differences.

Conclusion: All interventions were superior in reducing FM% compared to standard care. Adding exercise to a caloric restriction was superior in reducing FM% compared to a caloric restriction alone.

Background: Eccentric training, such as Nordic hamstring exercise (NHE) training, is commonly used as a preventive measure for hamstring strains. Eccentric training is believed to induce lengthening of muscle fascicles and to be associated with the addition of sarcomeres in series within muscle fibers. However, the difficulty in measuring sarcomere adaptation in human muscles has severely limited information about the precise mechanisms of adaptation. This study addressed this limitation by measuring the multiscale hamstring muscle adaptations in response to 9 weeks of NHE training and 3 weeks of detraining.

Methods: Twelve participants completed 9 weeks of supervised NHE training, followed by a 3-week detraining period. We assessed biceps femoris long-head (BFlh) muscle fascicle length, sarcomere length, and serial sarcomere number in the central and distal regions of the muscle. Additionally, we measured muscle volume and eccentric strength at baseline, post-training, and post-detraining.

Results: NHE training over 9 weeks induced significant architectural and strength adaptations in the BFlh muscle. Fascicle length increased by 19% in the central muscle region and 33% in the distal muscle region. NHE also induced increases in serial sarcomere number (25% in the central region and 49% in the distal region). BFlh muscle volume increased by 8%, and knee flexion strength increased by 40% with training. Following 3 weeks of detraining, fascicle length decreased by 12% in the central region and 16% in the distal region along with reductions in serial sarcomere number.

Conclusion: Nine weeks of NHE training produced substantial, region-specific increases in BFlh muscle fascicle length, muscle volume, and force generation. The direct measurement of sarcomere lengths revealed that the increased fascicle length was accompanied by the addition of sarcomeres in series within the muscle fascicles.