The Effect of Strength Training on Vastus Lateralis' Stiffness: An Ultrasound Quasi-Static Elastography Study

Acute and Chronic Effects of Stretching on Running Economy: A Systematic Review with Meta-Analysis

BACKGROUND

Running economy (RE) determines the performance of endurance athletes. While stretching has been practised for decades, and is still one common integral component of warm-up routine, muscle stretching is also associated with decreased stiffness. For RE energy storage in the tendons which is accompanied with stiffness is of crucial importance. In turn, avoidance of pre-running stretching was frequently recommended. Although some studies supported this recommendation, the evidence is controversial. Nevertheless, yet, no systematic review on the effects of stretching on RE with effect size (ES) quantification was performed. Consequently, with this systematic review with meta-analysis, we aim to provide the first overview on this topic.

METHODS

In adherence to PRISMA 2020 guidelines, we meta-analyzed effect sizes from three databases using PICOS guidelines on stretching effects on RE in healthy participants using robust variance estimation. Heterogeneity was reduced using subgroup analyses while meta-regression evaluated whether running velocity potentially moderates results. Risk of Bias was assessed using the PEDro scale, certainty of evidence was classified via GRADE working group criteria. The study protocol was registered in Open Science Framework https://doi.org/10.17605/OSF.IO/MA8D4 ).

RESULTS

Overall, low certainty of evidence pooled from 15 studies with a total of 181 participants indicated that stretching did not significantly moderate RE acutely (p = 0.21-0.65), neither in general, nor were there any stretching types (dynamic, static and proprioceptive neuromuscular facilitation) that affected this result. Due to the limited number of chronic studies found in the literature, long-term stretching effects were exclusively evaluated qualitatively. Meaningful heterogeneity and reduced methodological quality (PEDro Score: 4.88, fair) contributed to certainty of evidence downgrading.

CONCLUSIONS

In contrast to common beliefs that stretching decreased stiffness parameters and would therefore hamper RE, current evidence does not support any effect of stretching on RE in running athletes. However, several flaws such as no investigation of the underlying mechanisms (e.g., stiffness), small sample sizes, determining RE at different velocities, and the implementation of unreasonable stretching durations strongly biased conclusions. Especially on chronic effects there is a large demand for improved evidence, including underlying mechanisms investigation. Yet, it seems unreasonable to avoid pre-running stretching to prevent RE decreases.

Does exercise training combined with blood flow restriction improve muscle mass, lower extremity function, and walking capacity in hemiplegic patients? A randomized clinical trial

BACKGROUND

Blood flow restriction creates a state with increased motor function that permits treatment modalities to induce muscle hypertrophy. Blood flow-restricted exercise training (BFRET) may induce motor learning and boost the facilitatory effect of exercise training (ET).

OBJECTIVE

This study investigated the effects of BFRET on post-stroke hemi paretic lower extremity function and walking capacity recovery.

METHODOLOGY

This randomized clinical trial was conducted from September 2021 to October 2022 at the Department of Rehabilitation Medicine of the Second Affiliated Hospital of Chongqing Medical University in China. Participants were randomized 1:1 to BFRET or ET, each involving 30 minutes of training twice per day for 4 weeks.

MAIN OUTCOMES MEASURES

The main outcomes were manual muscle testing (MMT) and Fugl-Meyer assessment scale-lower extremity (FMA-LE), the timed up and go test (TUGT), Outcomes were assessed by blinded raters after 4 weeks of training.

RESULTS

40 participants mean [SD] age 48.79[12.58] years, 30 males [75%], 20 were randomized to BFRET and 20 to ET. The mean (SD) time since stroke was 2.5 (1.3) years. The MMT scores showed greater strength by within-group comparisons and superior changes in hip flexion and plantar flexion in the BFRET group.

CONCLUSIONS

BFRET is superior to ET alone in enhancing muscle mass and strength in the lower extremities. BFRET may improve the function of the lower extremities through physiological adaptations for muscle hypertrophy.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: ChiCTR2100050206.

Evaluation of the core muscles of children and adolescents with nocturnal enuresis using shear wave elastography: a preliminary study

The purpose of this study was to determine any changes in the rectus abdominis and diaphragm muscles, which are core muscles, in children and adolescents with nocturnal enuresis (NE) using the shear wave elastography (SWE). In this case-control study, the rectus abdominis and diaphragm muscles of 40 children and adolescents with NE and 40 healthy controls were evaluated. The rectus abdominis muscle was examined at the right supra- and subumbilical levels, and the diaphragm at the right 9th-10th intercostal space. The thickness of both muscles was measured by gray scale ultrasound and muscle stiffness was measured by SWE. The demographic characteristics of the patients such as sex and age and their anthropometric measurements including height, weight, and BMI were recorded. Compared to the control group, the NE group had significantly lower mean rectus abdominis muscle stiffness values on both the supraumbilical and subumbilical levels (p < 0.05). There was no significant difference in mean rectus abdominis thickness and diaphragm thickness-stiffness values between the groups (p > 0.05). According to the results of the study, it is thought that NE children have problems with core stabilization and that children with NE should be directed to appropriate treatment. However, future studies are needed with larger sample sizes and other factors that are thought to affect muscle architecture.

Effects of flywheel resistance training on countermovement jump performance and vastus lateralis muscle stiffness: A controlled study

This study aimed to investigate the effects of an 8-week resistance training using flywheel (FW) device on countermovement jump (CMJ) performance and resting stiffness of the vastus lateralis (VL) muscle. Physically active adults were randomly assigned to a training intervention group (T; n = 18) and a control group (C; n = 13), which received no intervention. Jump performance variables and ultrasound-assessed resting VL shear modulus were measured before and after the intervention. Analysis of covariance revealed statistically significant group differences in jump height (T =  +9%; C = -3%), rate of force development (T =  +32%; C =  +4%), peak power (T =  +9%; C = -1%), and peak force (T =  +7%; C = -1%). Jump performance improved only in the training group (all CMJ variables p < 0.05). Conversely, no significant changes within groups were observed in the resting shear wave modulus results (p > 0.05). VL stiffness decreased in the training group (-4%) and increased in the control group (+6%). Our results suggest that resistance training using FW device with individually allocated high-load FW inertia induces significant improvements in jump performance, which are not underpinned by changes in VL muscle stiffness.

Myofascial System and Physical Exercise: A Narrative Review on Stiffening (Part II)

In the past two decades, interest in the fascial system has exponentially increased, particularly manual treatment and stretching exercises. The fascia's fundamental role remains the transmission of tensions, although this function can be impaired due to excessive or reduced stiffness. This second part of the work outlines the basic principles concerning the importance of appropriate and balanced fascial stiffness for correct postural and functional maintenance of the human body. Additionally, the limited studies available in the literature are reviewed, with a focus on therapeutic exercises aimed at increasing fascial system stiffness. The article addresses how fascia develops the ability to contract to maintain a physiological tension referred to as human resting myofascial tone. Additionally, it discusses the most recognized tools for assessing fascial tension: myotonometry and shear wave elastography. The final section is dedicated to presenting the current literature on the relationship between physical exercise and fascial stiffness.

Automatic Quantitative Assessment of Muscle Strength Based on Deep Learning and Ultrasound

Skeletal muscle is a vital organ that promotes human movement and maintains posture. Accurate assessment of muscle strength is helpful to provide valuable insights for athletes' rehabilitation and strength training. However, traditional techniques rely heavily on the operator's expertise, which may affect the accuracy of the results. In this study, we propose an automated method to evaluate muscle strength using ultrasound and deep learning techniques. B-mode ultrasound data of biceps brachii of multiple athletes at different strength levels were collected and then used to train our deep learning model. To evaluate the effectiveness of this method, this study tested the contraction of the biceps brachii under different force levels. The classification accuracy of this method for grade 4 and grade 6 muscle strength reached 98% and 96%, respectively, and the overall average accuracy was 93% and 87%, respectively. The experimental results confirm that the innovative methods in this paper can accurately and effectively evaluate and classify muscle strength.

Effect of Knee Angle, Contractile Activity, and Intensity of Force Production on Vastus Lateralis Stiffness: A Supersonic Shear Wave Elastography Pilot Study

Supersonic shear image (SSI) ultrasound elastography provides a quantitative assessment of tissue stiffness using the velocity of shear waves. SSI's great potential has allowed researchers in fields like biomechanics and muscle physiology to study the function of complex muscle groups in different conditions. The aim of this study is to use SSI to investigate changes in the stiffness of the vastus lateralis (VL) muscle as a consequence of passive elongation, isometric contraction, and repeated muscle activity. In a single session, 15 volunteers performed a series of isometric, concentric, and eccentric contractions. SSI images were collected from the VL to assess its stiffness before and after the contractions and at various knee angles. Two-way within-subjects ANOVA was used to test the effects of muscle contraction type and knee angle on VL stiffness. Linear regression analysis was employed to assess the relationship between muscle stiffness and the intensity of isometric contractions. After maximal contractions, VL stiffness increased by approximately 10% compared to baseline values, and following maximal isometric (p < 0.01) and eccentric contractions (p < 0.05). Yet, there was no change in VL shear modulus at the end of concentric contractions. The relaxed VL shear modulus increased with knee flexion both before and after the knee extensor contractions (p < 0.001). A linear relationship between the shear modulus and the degree of isometric contraction was observed, although with notable individual variation (R2 = 0.125). Maximal contractile activity produces modest increases in relaxed muscle stiffness. The SSI-measured shear modulus increases linearly with the degree of isometric contraction.

Comparative Study of Muscle Hardness during Water-Walking and Land-Walking Using Ultrasound Real-Time Tissue Elastography in Healthy Young People

Compared with land-walking, water-walking is considered to be beneficial as a whole-body exercise because of the characteristics of water (buoyancy, viscosity, hydrostatic pressure, and water temperature). However, there are few reports on the effects of exercise in water on muscles, and there is no standard qualitative assessment method for muscle flexibility. Therefore, we used ultrasound real-time tissue elastography (RTE) to compare muscle hardness after water-walking and land-walking. Participants were 15 healthy young adult males (24.8 ± 2.3 years). The method consisted of land-walking and water-walking for 20 min on separate days. The strain ratio of the rectus femoris (RF) and medial head of gastrocnemius (MHGM) muscles were measured before and immediately after walking using RTE to evaluate muscle hardness. In water-walking, the strain ratio significantly decreased immediately after water-walking, with p < 0.01 for RF and p < 0.05 for MHGM, indicating a significant decrease in muscle hardness after water-walking. On the other hand, land-walking did not produce significant differences in RF and MHGM. Muscle hardness after aerobic exercise, as assessed by RTE, was not changed by land walking but was significantly decreased by water walking. The decrease in muscle hardness induced by water-walking was thought to be caused by the edema reduction effect produced by buoyancy and hydrostatic pressure.

Effects of Different Long-Term Exercise Modalities on Tissue Stiffness

Stiffness is a fundamental property of living tissues, which may be modified by pathologies or traumatic events but also by nutritional, pharmacological and exercise interventions. This review aimed to understand if specific forms of exercise are able to determine specific forms of tissue stiffness adaptations. A literature search was performed on PubMed, Scopus and Web of Science databases to identify manuscripts addressing adaptations of tissue stiffness as a consequence of long-term exercise. Muscular, connective, peripheral nerve and arterial stiffness were considered for the purpose of this review. Resistance training, aerobic training, plyometric training and stretching were retrieved as exercise modalities responsible for tissue stiffness adaptations. Differences were observed related to each specific modality. When exercise was applied to pathological cohorts (i.e. tendinopathy or hypertension), stiffness changed towards a physiological condition. Exercise interventions are able to determine tissue stiffness adaptations. These should be considered for specific exercise prescriptions. Future studies should concentrate on identifying the effects of exercise on the stiffness of specific tissues in a broader spectrum of pathological populations, in which a tendency for increased stiffness is observed.

The effect of Liquid ice after high-intensity exercise on muscle function compared to Block ice

Cryotherapy is used to recover muscle damage after exercise and to treat acute sports injuries. Liquid ice (LI) can keep cold for a long time, and is assumed more effective than block ice (BI). From this, the aim of this study was to investigate the effects of LI on the change of passive stiffness (PS) as muscle function and to validate the effectiveness of LI compared to BI. We performed the experiment as part of a case series of verification of the effects of cryotherapy. 22 healthy men (target area: right leg) were randomized to two groups: LI group and BI group. PS was measured three times during experiment protocol, pre: before exercise; post; after treating each cryotherapy after exercise; 48h: 48 hours after pre. Statistical analysis compared the PS, the amount of change in PS, and the rate of change in PS between the two groups. The rate of change between pre and 48h in LI was significantly lower compared to that in BI (p = 0.03). There was no significant difference regarding other results between groups. It revealed that the difference of effect between LI and BI for PS of muscles after high-intensity exercises. These results could be helpful for the choice of intervention for reducing muscle stiffness after exercise and at sports field.