Frontiers in Physiology最新文献

Introduction: The aim of the present study was to investigate the effects of eccentric phase tempo in squats on hypertrophy, strength, and contractile properties of the quadriceps femoris (QF) muscle.

Methods: Eighteen participants (10 males and 8 females, age 24.0 ± 1.7 years) with no resistance training (RT) experience in the last 8 months were randomized into two groups, each following a 7 week squat resistance training (RT) protocol with either a fast eccentric (FE, 1 s eccentric/0 s isometric/1 s concentric/0 s isometric) or slow eccentric (SE, 4 s eccentric/0 s isometric/1 s concentric/0 s isometric) tempo. The training intensity (60%-70% RM), the number of sets (3-4), and the rest intervals (120 s) were consistent in both groups. The study measured changes in quadriceps cross-sectional area (CSA), one-repetition maximum (1RM) strength, and muscle contractile properties such as contraction time (Tc) and radial displacement (Dm), using tensiomyography (TMG). An ANCOVA model with baseline values as covariates was used to examine between-group differences.

Results: Results showed significant strength gains in both groups, with the SE group achieving greater 1RM increases (effect size [ES] = 1.60 vs 0.99, p < 0.05). CSA increased for all QF muscles; however, the SE group exhibited significantly higher hypertrophy in the vastus lateralis (ES = 1.74 vs. 1.37, p < 0.05). TMG analysis revealed decreased Dm in the rectus femoris for both groups (p < 0.05), while Tc significantly (ES = 1.33, p < 0.01) increased in the SE group.

Discussion: These findings suggest that slower eccentric tempo in RT may optimize vastus lateralis hypertrophy and enhance strength while promoting muscle fiber-type specificity, contributing to the understanding of eccentric training's role in muscle adaptation.

Introduction: Recent findings show that visible light, particularly blue light, stimulates melanogenesis in human skin, though the underlying mechanisms remain debated. This study aimed to determine the cell damage threshold of non-ionizing blue light on keratinocytes while preserving their ability to stimulate melanogenesis.

Methods: Human keratinocytes (N = 3) and melanocytes (N = 3) were isolated from skin samples of varying Fitzpatrick skin phototypes and irradiated with blue light (λpeak = 457 nm) and UVA light (λpeak = 385 nm). Cellular metabolic activity was assessed using the AlamarBlue HS assay, α-Melanocyte-Stimulating Hormone (α-MSH) production by keratinocytes was quantified using ELISA, and Western blotting was used to assess pro-melanogenic factor expression in melanocytes.

Results: High blue light intensity (50 mW/cm², 50 J/cm²) and UVA light (15 mW/cm², 20 J/cm²) significantly reduced cellular metabolic activity, with a 0.86 ± 0.055 and 0.60 ± 0.031 (mean ± SD) fold decrease compared to their respective sham by day 7. In contrast, moderate blue light intensities (5-15 mW/cm², 10-20 J/cm²) preserved cellular metabolic activity while stimulating α-MSH production, with an optimal balance achieved at 10 mW/cm², 15 J/cm² (1.14 ± 0.046 fold increase relative to sham on day 7). Co-culture experiments confirmed that irradiated keratinocytes enhanced melanogenesis in melanocytes via paracrine signaling, increasing the expression of Tyrosinase and Dopachrome Tautomerase (DCT). Direct blue light irradiation on melanocytes also increased pigmentation without significant cellular damage.

Discussion: Moderate-intensity blue light at 10 mW/cm², 15 J/cm² effectively stimulates melanogenesis while maintaining cellular metabolic activity in both keratinocytes and melanocytes, offering a promising, safe approach for blue light therapies targeting pigmentation disorders.

Purpose: The purpose of this study was to examine the effects of a 7-week supplemental BFR training intervention on both acute and chronic alterations in salivary testosterone (sTes) and cortisol (sCort) in collegiate American football players.

Methods: 58 males were divided into 4 groups: 3 completed an upper- and lower-body split resistance training routine (H, H/S, H/S/R; H = Heavy, S = Supplemental, R = BFR), with H/S/R performing end-of-session practical BFR training, and H/S serving as the volume-matched non-BFR group. The final group (M/S/R) completed modified resistance training programming with the same practical BFR protocol as H/S/R. Athletes were further split into AM and PM training groups based upon their pre-determined training schedules, in cooperation with University strength and conditioning staff. Practical BFR consisted of end-of-session barbell bench press and back squat using 20% 1 repetition maximum (1RM) for 30-20-20-20 repetitions across 4 sets, with 45-seconds rest. Saliva samples were taken pre- and post- the first lower-body training sessions in week 1 and week 7 (i.e., test 1 and test 2) of the program, yielding four total. sTes and sCort were analyzed using 4-way (4 × 2 × 2 × 2) mixed model ANOVA's.

Results: Hormonal variables all exhibited main effects for time-of-day (p < 0.001). A significant group × time interaction effect (F_3,50 = 3.246, p < 0.05) indicated increases in sTes post-training cycle for the H/S/R group only. Further, PM post-exercise sCort decreased from test 1 to test 2 (nmol·L^-1: 95% CI: PM test 1 post-exercise = 10.7-17.1, PM test 2 post-exercise = 5.0-8.9). For the testosterone-to-cortisol ratio (T/C), AM pre-exercise was lower than PM (p < 0.05), with no change in post-exercise T/C for both AM and PM conditions when collapsed across testing times.

Discussion: Overall, these findings suggest an ecologically valid method of BFR implementation is capable of inducing heightened concentrations of sTes in well-resistance trained American football athletes, providing additional insight on possible physiological mechanisms underpinning BFR's ability to elicit beneficial muscle hypertrophy and maximal strength adaptations when performed during regimented training programs. Additionally, notable rises in T/C, and a null sCort response post-exercise were observed post-program for all groups, possibly indicative of positive physiological adaptation.

Introduction: This study aimed to assess the development of speed, endurance and power in young football players and to create percentile charts and tables for standardized assessment.

Methods: Cross-sectional data were collected from 495 male players aged 12-16 years at RKS Raków Częstochowa Academy in 2018-2022. Players participated in a systematic training in which running time 5 m, 10 m, 30 m, lower limb power (standing long jump), and Maximum Aerobic Speed (MAS) were measured using the 30-15 Intermittent Fitness Test. All tests were performed under constant environmental conditions by qualified personnel. Statistical analysis included ANOVA and percentile distribution for P3, P10, P25, P50, P75, P90, P97.

Results: Results indicated that the most significant improvements occurred between the ages of 13 and 14, with increased speed over all distances and a significant increase in power. Percentile tables were developed, highlighting improvements in speed 5 m: 0.087-0.126 s; 10 m 0.162-0.215 s; 30 m: 0.438-0.719 s and power in the long jump test: 31-48 cm. Improvements in MAS ranged from 0.3 to 0.6 m/s across the percentiles.

Discussion: The results highlight the need for individual training programs tailored to the biological maturity of players. The developed percentile charts and tables offer a valuable tool for coaches and sports scientists to monitor progress, optimize training loads, and minimize the risk of injury, providing a frame of reference for assessing the physical development of young soccer players. Future research should focus on extending these charts and tables to other age groups and genders to refine training methodologies further.

This study aims to assess the reliability and accuracy of a novel portable cardiopulmonary function meter, "Booster," developed by our research group, across various exercise intensities and modalities. The study was segmented into reliability and validity assessments. Twenty-two male participants underwent reliability testing, conducting two sequential tests on a treadmill while wearing the Booster to measure VO₂ and VE among other parameters at increasing intensities. For validity testing, 64 participants were randomly divided into treadmill and cycle ergometer groups, with tests conducted using both the Booster and the Cortex Metalyzer 3B systems. Overall, the Booster demonstrated high retest reliability for VO₂ and VE measurements during treadmill exercises, albeit showing poor consistency during rest and low-intensity exercise phases. Validity testing indicated no significant differences in VO₂ and VE measurements between Booster and Cortex Metalyzer 3B across all exercise stages on both treadmill and cycle ergometer, suggesting good correlation. However, discrepancies in measurements between Booster and Cortex Metalyzer 3B were observed during rest and maximal exertion phases. The Booster exhibits commendable reliability and stability during most treadmill exercise phases and shows generally acceptable validity compared to the Cortex Metalyzer 3B system. Nonetheless, potential measurement discrepancies may occur during rest and maximal exertion conditions.

Skeletal muscle (SKM) has crucial roles in locomotor activity and posture within the body and also functions have been recognized as an actively secretory organ. Numerous bioactive molecules are secreted by SKM and transported by extracellular vesicles (EVs), a novel class of mediators of communication between cells and organs that contain various types of cargo molecules including lipids, proteins and nucleic acids. SKM-derived EVs (SKM-EVs) are intercellular communicators with significant roles in the crosstalk between SKM and other organs. In this review, we briefly describe the biological characteristics, composition, and uptake mechanisms of EVs, particularly exosomes, comprehensively summarize the regulatory effects of SKM-EVs on the function of, which include myogenesis, muscle repair and regeneration, as well as metabolic regulation. Furthermore, we explore the impact of SKM- EVs on various organs including bone, the cardiovascular system, adipose tissue, and nervous system. As emerging evidence suggests that SKM-EVs are involved in the development and regulation of type 2 diabetes (T2D), systemic inflammation, and other chronic diseases, we also highlight the potential of SKM-EVs as therapeutic targets and diagnostic biomarkers, emphasizing the need for further research to elucidate the complex mechanisms underlying intercellular communication in physiological and pathological contexts.

Purpose: This study aimed to explore the effects of neural and muscular factors on lower limb explosive strength in male college sprinters, and build models based on those factors to identify the key neuromuscular factors that predict the rate of force development (RFD) and 30 m sprint time.

Method: 15 male college sprinters were recruited in this study, with 100 m personal best times under 10.93 s. The neuromuscular data were collected by H-reflex and V-wave, isokinetic muscle strength, vertical jumps, and 30 m sprint tests. Pearson correlation and multiple stepwise regression were used for data analysis. The level of statistical significance was set at p ≤ 0.05 for all analyses.

Results: 30 m sprint time had a significant moderate positive correlation with Achilles tendon stiffness (r = 0.50, p = 0.05, 95%CI: 0.01-0.81) and a significant moderate negative correlation with the H-index (r = -0.54, p = 0.04, 95%CI: 0.82 to -0.03), V wave (V/MmaxA, r = -0.59, p = 0.02, 95%CI: 0.85 to -0.11) and the eccentric strength of Hamstring (HECC, r = -0.53, p = 0.04, 95%CI: 0.82 to -0.03). The rate of force development (RFD) had a significant positive correlation with H reflex (Hmax/Mmax, r = 0.57, p = 0.03.95%CI:0.08-0.84), and the eccentric strength of Quadriceps (QECC, r = 0.53, p = 0.04, 95%CI: 0.02-0.82). V/MmaxA and HECC were identified as predictors of 30 m sprint time, and the R ² explained 57.5% of the variance. Vertical stiffness and QECC explained 82.7% of the variation in the RFD.

Conclusion: This study found that V/MmaxA and HECC were predictive factors of 30 m sprint time, vertical stiffness and QECC were the predictive factors of RFD. Neural factors such as the α-motoneurons excitability of the spinal and supraspinal centers, have a greater influence on lower limb explosive strength in male college sprinters. Therefore, training related to the neural function of sprinters should be emphasized. In addition, H reflex and V wave can be used widely to assess and monitor the neural function of sprinters in future research. The impact of neural drive on muscles in different levels and sexes of sprinters, and the neuromuscular modulation during muscle contractions can be further explored.

Introduction: The effect of mechanoreflex on central blood pressure (BP) is unclear, although the influence of metaboreflex has been investigated. A relatively small contribution of the mechanoreflex to the pressor response to exercise has been considered in humans because many studies have failed to isolate the mechanoreflex-mediated pressor response. In a recent study, we successfully isolated a mechanoreflex-mediated pressor response using static passive stretching (SPS) in the forearm. Thus, it is possible to isolate the effect of the mechanoreflex on the central BP using this recently developed method. We investigated the effect of muscle mechanoreflex on central BP and compared the changes in the shape of the central BP waveform during mechanoreflex and metaboreflex.

Methods: We measured 12 healthy males (age, 26 ± 2 years; height, 171.1 ± 5.2 cm; body mass, 63.3 ± 10.3 kg; body fat, 16.7% ± 3.9%; means ± standard deviation [SD]) in this study. All participants performed static passive stretching (SPS) of the forearm for 60 s to isolate the muscle mechanoreflex. They also performed 120 s of isometric handgrip (IHG) at 30% maximal voluntary contraction and underwent 180 s of post-exercise ischemia (PEI) to isolate the muscle metaboreflex. The carotid BP (cBP) waveform was obtained from the right common carotid artery as the central BP waveform. We evaluated the first systolic peak (P1) and second systolic peak (P2) from the cBP waveform.

Results: SPS increased cBP with an increase in P1 (p < 0.05), whereas PEI increased cBP with an increase in P2 (p < 0.05). SPS did not alter augmentation pressure (AP) (p > 0.05), whereas PEI increased it (p < 0.05). The relative change from rest (Δ) in P1 during SPS was positively correlated with that in stroke volume (r = 0.68; p < 0.05), and the ΔAP during PEI was positively correlated with that in total peripheral resistance TPR (r = 0.61; p < 0.05).

Conclusion: These results suggest different effects of mechano- and metaboreflex on the change in shape of the central BP waveform; mechanoreflex and metaboreflex deform P1 and P2, respectively.