Inhomogeneous architectural changes of the quadriceps femoris induced by resistance training

Effect of resistance training on quadriceps femoris muscle thickness obtained by ultrasound: A systematic review with meta-analysis

OBJECTIVE

The present study aimed to determine the magnitude and intervention time of resistance training required to generate adaptations in the muscle thickness of the quadriceps muscle obtained by ultrasound in healthy adults.

METHOD

A systematic review with meta-analysis was conducted on studies recovered from Pubmed, Web of Science, and Scopus databases up to March 2022. The study selection process was carried out by two independent researchers, with the presence of a third researcher in case of disagreements. The methodological quality of the studies was determined with the TESTEX scale, and the risk of bias analysis was determined using Cochrane's RoB 2.0 tool. The meta-analysis used the inverse of the variance with a fixed model, and the effect size was reported by the standardized mean difference (SMD) with a confidence interval of 95%.

RESULTS

Ten studies were included in a meta-analysis. The overall analysis of the studies demonstrated an SMD = 0.35 [95% CI: 0.13-0.56] (P = 0.002), with a low heterogeneity of I2 = 0% (P = 0.52). No publication bias was detected using a funnel plot followed by Egger's test (P = 0.06). The degree of certainty of the meta-analysis was high using the GRADE tool.

CONCLUSION

We found that resistance training can generate significant average increases of 16.6% in muscle thickness obtained by ultrasound in the quadriceps femoris muscles of healthy adults. However, the subgroup analysis showed that significant effect sizes were only observed after eight weeks of training.

Biceps femoris long head stiffens after 2 weeks of training cessation in highly trained sprinters

PURPOSE

Most athletes experience short-term training cessation because of illness, injury, post-season vacation, or other reasons. Passive muscle stiffness is a potential risk factor for a sprint-type hamstring strain injury, but limited information is available about the effect of short-term training cessation on passive muscle stiffness. The present study aimed to identify whether and how passive muscle stiffness of the biceps femoris long head (BFlh) would vary due to 2 weeks of training cessation in sprinters.

METHODS

Passive BFlh shear-wave speed (a proxy for stiffness) was measured using ultrasound shear-wave elastography in 28 male sprinters, before and after 2 weeks of intervention. During the 2 weeks, the participants in the training-cessation group (n = 14) were allowed to maintain their normal daily activities but not to perform any physical training, including stretching and resistance exercises. The participants in the training continuation group (n = 14) performed the training (including maximum speed sprint, plyometric, and weight training) prescribed by their coaches 5 days per week.

RESULTS

In the training-cessation group, passive BFlh shear-wave speed increased after the 2 weeks of training cessation (4.75 ± 0.77 to 5.00 ± 0.88 m/s, P < 0.001). In contrast, there was no significant difference before and after the 2 weeks of training continuation (4.90 ± 0.85 to 4.93 ± 0.85 m/s, P = 0.521).

CONCLUSIONS

The present findings indicate that muscles stiffen by training cessation in sprinting athletes.

Effect of applied cadence in repeated sprint cycling on muscle characteristics

PURPOSE

This study aimed to investigate physiological responses, muscle-tendon unit properties of the quadriceps muscle, and mechanical performance after repeated sprint cycling at optimal and 70% of optimal cadence.

METHODS

Twenty recreational cyclists performed as first sprint performance cycling test and during subsequent sessions two repeated sprint cycling protocols at optimal and 70% of optimal cadence, in random order. The muscle-tendon unit outcome measures on the dominant leg included muscle thickness, fascicle length (Lf), pennation angle (θp), and stiffness for the rectus femoris (RF), vastus lateralis (VL), and vastus medialis muscle (VM) at baseline, immediately after repeated sprint cycling, and 1-h post-exercise.

RESULTS

The results showed an increase in muscle thickness and θp in RF, VL, and VM for both cadences from baseline to immediately after exercise. The Lf decreased in RF (both cadences), while stiffness decreased in RF, VL, and VM at optimal cadence, and in VL at 70% of optimal cadence from baseline to immediately after exercise.

CONCLUSION

The present study revealed that the alterations in muscle characteristics were more marked after repeated sprint cycling at optimal cadence compared with a lower cadence most likely as a result of higher load on the muscle-tendon unit at optimal cadence.

Determining Changes in Muscle Size and Architecture After Exercise Training: One Site Does Not Fit all

ABSTRACT

Nunes, JP, Blazevich, AJ, Schoenfeld, BJ, Kassiano, W, Costa, BDV, Ribeiro, AS, Nakamura, M, Nosaka, K, and Cyrino, ES. Determining changes in muscle size and architecture after exercise training: One site does not fit all. J Strength Cond Res 38(4): 787-790, 2024-Different methods can be used to assess muscle hypertrophy, but the effects of training on regional changes in muscle size can be detected only using direct muscle measurements such as muscle thickness, cross-sectional area, or volume. Importantly, muscle size increases vary across regions within and between muscles after resistance training programs (i.e., heterogeneous, or nonuniform, muscle hypertrophy). Muscle architectural changes, including fascicle length and pennation angle, after resistance and stretch training programs are also region-specific. In this paper, we show that the literature indicates that a single-site measure of muscle shape does not properly capture the effects achieved after exercise training interventions and that conclusions concerning the magnitude of muscle adaptations can vary substantially depending on the muscle site to be examined. Thus, we propose that measurements of muscle size and architecture should be completed at multiple sites across regions between the agonist muscles within a muscle group and along the length of the muscles to provide an adequate picture of training effects.

Chronic Effects of Inter-Set Static Stretching on Morphofunctional Outcomes in Recreationally Resistance-Trained Male and Female

Purpose: The purpose of this study was to compare the effects of resistance training (RT) with inter-set static stretching (IS) versus traditional RT (TRT) on morphofunctional outcomes in recreationally resistance-trained male and female. Methods: Twenty-two recreationally-trained subjects were allocated to IS group (n = 12) or TRT (n = 10) and completed eight weeks of RT. The only difference between the groups was that IS group included static stretching between sets, while the TRT rested between the sets. Ultrasound images, dynamic and isometric strength tests for the elbow flexors and elbow extensors were evaluated pre- and post-intervention period. Results: Total training volume (TTV) was greater in TRT than IS (p = .031). TRT and IS caused similar increases in maximal dynamic and isometric strength. Fascicle length of the brachialis increased following TRT (p = .033); muscle thickness and the pennation angle of the distal portion of the triceps brachii increased following IS (p = .035 and p = .007, respectively). There were no significant changes in thickness and architecture for biceps brachii in either group. There were no significant differences between groups for any muscle strength and morphology outcome. Conclusion: IS negatively affects TTV but does not affect muscle strength and architecture of recreationally resistance-trained male and female.

A single bout of prior resistance exercise attenuates muscle atrophy and declines in myofibrillar protein synthesis during bed-rest in older men

Impairments in myofibrillar protein synthesis (MyoPS) during bed rest accelerate skeletal muscle loss in older adults, increasing the risk of adverse secondary health outcomes. We investigated the effect of prior resistance exercise (RE) on MyoPS and muscle morphology during a disuse event in 10 healthy older men (65-80 years). Participants completed a single bout of unilateral leg RE the evening prior to 5 days of in-patient bed-rest. Quadriceps cross-sectional area (CSA) was determined prior to and following bed-rest. Serial muscle biopsies and dual stable isotope tracers were used to determine rates of integrated MyoPS (iMyoPS) over a 7 day habitual 'free-living' phase and the bed-rest phase, and rates of acute postabsorptive and postprandial MyoPS (aMyoPS) at the end of bed rest. Quadriceps CSA at 40%, 60% and 80% of muscle length significantly decreased in exercised (EX) and non-exercised control (CTL) legs with bed-rest. The decline in quadriceps CSA at 40% and 60% of muscle length was attenuated in EX compared with CTL. During bed-rest, iMyoPS rates decreased from habitual values in CTL, but not EX, and were significantly different between legs. Postprandial aMyoPS rates increased above postabsorptive values in EX only. The change in iMyoPS over bed-rest correlated with the change in quadriceps CSA in CTL, but not EX. A single bout of RE attenuated the decline in iMyoPS rates and quadriceps atrophy with 5 days of bed-rest in older men. Further work is required to understand the functional and clinical implications of prior RE in older patient populations. KEY POINTS: Age-related skeletal muscle deterioration, linked to numerous adverse health outcomes, is driven by impairments in muscle protein synthesis that are accelerated during periods of disuse. Resistance exercise can stimulate muscle protein synthesis over several days of recovery and therefore could counteract impairments in this process that occur in the early phase of disuse. In the present study, we demonstrate that the decline in myofibrillar protein synthesis and muscle atrophy over 5 days of bed-rest in older men was attenuated by a single bout of unilateral resistance exercise performed the evening prior to bed-rest. These findings suggest that concise resistance exercise intervention holds the potential to support muscle mass retention in older individuals during short-term disuse, with implications for delaying sarcopenia progression in ageing populations.

Effect of free-weight vs. machine-based strength training on maximal strength, hypertrophy and jump performance - a systematic review and meta-analysis

BACKGROUND

The effectiveness of strength training with free-weight vs. machine equipment is heavily debated. Thus, the purpose of this meta-analysis was to summarize the data on the effect of free-weight versus machine-based strength training on maximal strength, jump height and hypertrophy.

METHODS

The review was conducted in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, and the systematic search of literature was conducted up to January 1st, 2023. Studies that directly compared free-weight vs. machine-based strength training for a minimum of 6 weeks in adults (18-60 yrs.) were included.

RESULTS

Thirteen studies (outcomes: maximal strength [n = 12], jump performance [n = 5], muscle hypertrophy [n = 5]) with a total sample of 1016 participants (789 men, 219 women) were included. Strength in free-weight tests increased significantly more with free-weight training than with machines (SMD: -0.210, CI: -0.391, -0.029, p = 0.023), while strength in machine-based tests tended to increase more with machine training than with free-weights (SMD: 0.291, CI: -0.017, 0.600, p = 0.064). However, no differences were found between modalities in direct comparison (free-weight strength vs. machine strength) for dynamic strength (SMD: 0.084, CI: -0.106, 0.273, p = 0.387), isometric strength (SMD: -0.079, CI: -0.432, 0.273, p = 0.660), countermovement jump (SMD: -0.209, CI: -0.597, 0.179, p = 0.290) and hypertrophy (SMD: -0.055, CI: -0.397, 0.287, p = 0.751).

CONCLUSION

No differences were detected in the direct comparison of strength, jump performance and muscle hypertrophy. Current body of evidence indicates that strength changes are specific to the training modality, and the choice between free-weights and machines are down to individual preferences and goals.

ADAPTations to low load blood flow restriction exercise versus conventional heavier load resistance exercise in UK military personnel with persistent knee pain: protocol for the ADAPT study, a multi-centre randomized controlled trial

BACKGROUND

Muscle atrophy, muscle weakness and localised pain are commonly reported following musculoskeletal injury (MSKI). To mitigate this risk and prepare individuals to return to sport or physically demanding occupations, resistance training (RT) is considered a vital component of rehabilitation. However, to elicit adaptations in muscle strength, exercise guidelines recommend lifting loads ≥ 70% of an individual's one repetition maximum (1-RM). Unfortunately, individuals with persistent knee pain are often unable to tolerate such high loads and this may negatively impact the duration and extent of their recovery. Low load blood flow restriction (LL-BFR) is an alternative RT technique that has demonstrated improvements in muscle strength, hypertrophy, and pain in the absence of high mechanical loading. However, the effectiveness of high-frequency LL-BFR in a residential rehabilitation environment remains unclear. This study will compare the efficacy of high frequency LL-BFR to 'conventional' heavier load resistance training (HL-RT) on measures of physical function and pain in adults with persistent knee pain.

METHODS

This is a multicentre randomised controlled trial (RCT) of 150 UK service personnel (aged 18-55) admitted for a 3-week residential rehabilitation course with persistent knee pain. Participants will be randomised to receive: a) LL-BFR delivered twice daily at 20% 1-RM or b) HL-RT three-times per week at 70% 1-RM. Outcomes will be recorded at baseline (T1), course discharge (T2) and at three-months following course (T3). The primary outcome will be the lower extremity functional scale (LEFS) at T2. Secondary outcomes will include patient reported perceptions of pain, physical and occupational function and objective measures of muscle strength and neuromuscular performance. Additional biomechanical and physiological mechanisms underpinning both RT interventions will also be investigated as part of a nested mechanistic study.

DISCUSSION

LL-BFR is a rehabilitation modality that has the potential to induce positive clinical adaptations in the absence of high mechanical loads and therefore could be considered a treatment option for patients suffering significant functional deficits who are unable to tolerate heavy load RT. Consequently, results from this study will have a direct clinical application to healthcare service providers and patients involved in the rehabilitation of physically active adults suffering MSKI.

TRIAL REGISTRATION

ClinicalTrials.org reference number, NCT05719922.

The effects of hip- vs. knee-dominant hamstring exercise on biceps femoris morphology, strength, and sprint performance: a randomized intervention trial protocol

BACKGROUND

The hamstrings are an important muscle group that contribute to horizontal force during sprint acceleration and are also the most injured muscle group in running-based sports. Given the significant time loss associated with hamstrings injury and impaired sprinting performance following return to sport, identifying exercises that drive adaptations that are both protective of strain injury and beneficial to sprint performance is important for the strength and conditioning professional. This paper describes the study protocol investigating the effects of a 6-week training program using either the hip-dominant Romanian deadlift (RDL) or the knee-dominant Nordic hamstring exercise (NHE) on hamstring strain injury risk factors and sprint performance.

METHODS

A permuted block randomized (1:1 allocation) intervention trial will be conducted involving young, physically-active men and women. A target sample size of 32 will be recruited and enrolled participants will undergo baseline testing involving extended-field-of-view ultrasound imaging and shear wave elastography of the biceps femoris long head muscle, maximal hamstrings strength testing in both the RDL and NHE, and on-field sprint performance and biomechanics. Participants will complete the 6-week training intervention using either the RDL or NHE, according to group allocation. Baseline testing will be repeated at the end of the 6-week intervention followed by 2 weeks of detraining and a final testing session. The primary outcome will be regional changes in fascicle length with secondary outcomes including pennation angle, muscle cross sectional area, hamstring strength, and maximal sprint performance and biomechanics. An exploratory aim will determine changes in shear wave velocity.

DISCUSSION

Despite extensive research showing the benefits of the NHE on reducing hamstring strain injury risk, alternative exercises, such as the RDL, may offer similar or potentially even greater benefits. The findings of this study will aim to inform future researchers and practitioners investigating alternatives to the NHE, such as the RDL, in terms of their effectiveness in reducing rates of hamstring strain injury in larger scale prospective intervention studies.

TRIAL REGISTRATION

The trial is prospectively registered on ClinicalTrials.gov (NCT05455346; July 15, 2022).

Muscle Architecture and Subcutaneous Fat Measurements of Rectus Femoris and Vastus Lateralis at Optimal Length Aided by a Novel Ultrasound Transducer Attachment

Purpose: This cross-sectional study determines the sensitivity of muscle architecture and fat measurements of the rectus femoris (RF) and vastus lateralis (VL) muscles from ultrasound images acquired with varying transducer tilt, using a novel transducer attachment, in healthy adults. Secondary objectives were to estimate intrarater and interrater reliability of image measurement and acquisition, respectively. Methods: Thirty healthy adults participated (15 women and 15 men; 25 [SD 2.5] y). Ultrasound image acquisition was conducted by two raters at different transducer tilts relative to the skin: estimated perpendicular, and five measured angles (80°, 85°, 90°, 95°, 100°) using the transducer attachment. Muscle thickness (MT), subcutaneous fat thickness (FT), pennation angle (PA), and fascicle length (FL) were measured. Sensitivity and reliability were assessed using intra-class correlation coefficients (ICCs) and standard error of measurements (SEMs). Results: MT and FT for RF and VL were not sensitive to transducer tilt. However, PA and FL were sensitive to transducer tilt. MT and FT for both muscles showed high ICCs and low SEMs for intrarater and interrater reliability. For PA of both muscles, standardizing transducer tilt improved interrater ICCs and lowered SEMs. Conclusion: MT and FT measurements of RF and VL acquired at 60° knee flexion are robust to varying transducer tilt angles. PA measurements benefit from standardizing transducer tilt.

The effect of specific bioactive collagen peptides on function and muscle remodeling during human resistance training

AIM

Bioactive collagen peptides (CP) have been suggested to augment the functional, structural (size and architecture), and contractile adaptations of skeletal muscle to resistance training (RT), but with limited evidence. This study aimed to determine if CP vs. placebo (PLA) supplementation enhanced the functional and underpinning structural, and contractile adaptations after 15 weeks of lower body RT.

METHODS

Young healthy males were randomized to consume either 15 g of CP (n = 19) or PLA (n = 20) once every day during a standardized program of progressive knee extensor, knee flexor, and hip extensor RT 3 times/wk. Measurements pre- and post-RT included: knee extensor and flexor isometric strength; quadriceps, hamstrings, and gluteus maximus volume with MRI; evoked twitch contractions, 1RM lifting strength, and architecture (with ultrasound) of the quadriceps.

RESULTS

Percentage changes in maximum strength (isometric or 1RM) did not differ between-groups (0.684 ≤ p ≤ 0.929). Increases in muscle volume were greater (quadriceps 15.2% vs. 10.3%; vastus medialis (VM) 15.6% vs. 9.7%; total muscle volume 15.7% vs. 11.4%; [all] p ≤ 0.032) or tended to be greater (hamstring 16.5% vs. 12.8%; gluteus maximus 16.6% vs. 12.9%; 0.089 ≤ p ≤ 0.091) for CP vs. PLA. There were also greater increases in twitch peak torque (22.3% vs. 12.3%; p = 0.038) and angle of pennation of the VM (16.8% vs. 5.8%, p = 0.046), but not other muscles, for CP vs. PLA.

CONCLUSIONS

CP supplementation produced a cluster of consistent effects indicating greater skeletal muscle remodeling with RT compared to PLA. Notably, CP supplementation amplified the quadriceps and total muscle volume increases induced by RT.

Does Back Squat Exercise Lead to Regional Hypertrophy among Quadriceps Femoris Muscles?

The present study investigated effects of squat resistance training on intermuscular hypertrophy of quadriceps femoris muscles (i.e., rectus femoris, RF; vastus intermedius, VI; vastus medialis, VM; and vastus lateralis, VL). Eighteen university students (age: 24.1 ± 1.7 years, 9 females) underwent 7 weeks of parallel squat training (2 days/week) preceded by a 2-week familiarization period. Squat strength (1RM) and cross-sectional area (CSA) of four quadriceps muscles were assessed at baseline and at the end of the study. At posttest, 1RM and CSA of quadriceps muscles significantly increased (p < 0.01), with moderate-to-large effect (ES = 1.25−2.11) for 1RM (8.33 ± 6.64 kg), VM CSA (0.12 ± 0.08 cm2), and VL CSA (0.19 ± 0.09 cm2) and small effect (ES = 0.89−1.13) for RF CSA (0.17 ± 0.15 cm2) and VI CSA (0.16 ± 0.18 cm2). No significant differences were found in the changes of CSA between muscles (F = 0.638, p = 0.593). However, the squat 1RM gain was significantly associated only with the changes in CSA of the VL muscle (r = 0.717, p < 0.001). The parallel squat resulted in significant growth of all quadriceps muscles. However, the novelty of this study is that the increase in strength is associated only with hypertrophy of the VL muscle.

Including the Eccentric Phase in Resistance Training to Counteract the Effects of Detraining in Women: A Randomized Controlled Trial

ABSTRACT

Coratella, G, Beato, M, Bertinato, L, Milanese, C, Venturelli, M, and Schena, F. Including the eccentric phase in resistance training to counteract the effects of detraining in women: a randomized controlled trial. J Strength Cond Res 36(11): 3023-3031, 2022-The current study compared the effects of concentric-based (CONC), eccentric-based (ECC), and traditional concentric-eccentric (TRAD) resistance training on muscle strength, mass, and architecture and the postdetraining retention of the training-induced effects in women. Sixty women were randomly assigned to unilateral volume-equated CONC, ECC, or TRAD knee extension training or control ( N = 15 per group). Before training, after an 8-week intervention period, and after an 8-week detraining period, isokinetic concentric, eccentric, and isometric torque were measured. In addition, thigh lean mass was assessed by dual X-ray absorptiometry and vastus lateralis thickness, pennation angle, and fascicle length by ultrasound. After training, concentric and isometric torque increased ( p < 0.05) similarly in all groups, whereas eccentric torque increased more in ECC than that in CONC (+13.1%, effect size (ES): 0.71 [0.04-1.38]) and TRAD (+12.6%, ES: 0.60 [0.12-1.08]). Thigh lean mass increased in ECC (+6.1%, ES: 0.47 [0.27-0.67]) and TRAD (+3.1%, ES: 0.33 [0.01-0.65]). Vastus lateralis thickness and pennation angle increased ( p < 0.05) similarly in all groups, whereas fascicle elongation was visible in ECC (+9.7%, ES: 0.92 [0.14-1.65]) and TRAD (+7.1%, ES: 0.64 [0.03-1.25]). After detraining, all groups retained ( p < 0.05) similar concentric torque. ECC and TRAD preserved eccentric torque ( p < 0.05), but ECC more than TRAD (+17.9%, ES: 0.61 [0.21-1.21]). All groups preserved isometric torque ( p < 0.05), but ECC more than CONC (+14.2%, ES: 0.71 [0.04-1.38]) and TRAD (+13.8%, ES: 0.65 [0.10-1.20]). Thigh lean mass and vastus lateralis fascicle length were retained only in ECC ( p < 0.05), pennation angle was preserved in all groups ( p < 0.05), and thickness was retained in CONC and ECC ( p < 0.05). Including the eccentric phase in resistance training is essential to preserve adaptations after detraining.

Using Shear-Wave Elastography to Assess Exercise-Induced Muscle Damage: A Review

Shear-wave elastography is a method that is increasingly used to assess muscle stiffness in clinical practice and human health research. Recently, shear-wave elastography has been suggested and used to assess exercise-induced muscle damage. This review aimed to summarize the current knowledge of the utility of shear-wave elastography for assessment of muscle damage. In general, the literature supports the shear-wave elastography as a promising method for assessment of muscle damage. Increases in shear modulus are reported immediately and up to several days after eccentric exercise, while studies using shear-wave elastography during and after endurance events are showing mixed results. Moreover, it seems that shear modulus increases are related to the decline in voluntary strength loss. We recommend that shear modulus is measured at multiple muscles within a muscle group and preferably at longer muscle lengths. While further studies are needed to confirm this, the disruption of calcium homeostasis seems to be the primary candidate for the underlying mechanism explaining the increases in shear modulus observed after eccentric exercise. It remains to be investigated how well the changes in shear modulus correlate with directly assessed amount of muscle damage (biopsy).

Agreement and reliability of lower limb muscle architecture measurements using a portable ultrasound device

High end ultrasonography devices lack in portability and are expensive. We investigated the agreement and reliability of a handheld and portable ultrasound system for human lower limb muscle architecture measurements. We captured ultrasound images of the rectus femoris (RF), vastus lateralis (VL) and gastrocnemius medialis (GM) in 36 active healthy participants (15 female, 21 male) at 50% of muscle length using the handheld Lumify (L12-4, linear-array 37 mm, Philips Healthcare, Amsterdam, Netherlands) and a high-end laboratory device (ACUSON Juniper, linear-array 54 mm, 12L3, SIEMENS Healthineers, Erlangen, Germany). We compared measurements of muscle fascicle length, pennation angle and thickness. To assess inter-session reliability of the Lumify system, participants were measured twice within 1 week. Comparing RF architecture measurements of both devices resulted in intra-class correlations (ICCs) ranging from 0.46–0.82 and standardized mean difference (SMDs) ranging from −0.45–0.05. For VL, ICCs ranged from 0.60–0.89 and SMDs ranged from −0.11–0.13. ICCs and SMDs for the GM ranged from 0.82–0.86 and −0.07–0.07. Calculating inter-session reliability for RF resulted in ICCs ranging from 0.44–0.76 and SMDs ranging from −0.38–0.15. For VL, ICCs and SMDs ranged from 0.57–0.75 and −0.13–0.02. ICCs for GM ranged from 0.75–0.92 and SMDs ranged from −0.15–0.16. Measurement of muscle thickness demonstrated the highest agreement (ICC ≥0.82) and reliability (ICC ≥0.75) across all muscles. The Lumify system was comparable to a high-end device and reliable for GM measurements. However, agreement and reliability were lower for the RF and VL. Of all evaluated architectural parameters, muscle thickness exhibited highest agreement and reliability.

Three-dimensional architecture of human medial gastrocnemius fascicles in vivo: Regional variation and its dependence on muscle size

Fascicle architecture (length and pennation angle) can vary regionally within a muscle. The architectural variability in human muscles has been evaluated in vivo, but the interindividual variation and its determinants remain unclear. Considering that within‐muscle non‐uniform changes in pennation angle are associated with change in muscle size by chronic mechanical loading, we hypothesized that the regional variation in fascicle architecture is dependent on interindividual variation in muscle size. To test this hypothesis, we reconstructed fascicles three‐dimensionally along and across the whole medial gastrocnemius in the right lower leg of 15 healthy adults (10 males and 5 females, 23.7 ± 3.3 years, 165.8 ± 8.3 cm, 61.9 ± 11.4 kg, mean ± standard deviation) in neutral ankle joint position with the knee fully extended, using magnetic resonance diffusion tensor imaging and tractography. The 3D‐reconstructed fascicles arose from the deep aponeurosis with variable lengths and angles both in sagittal and coronal planes. The fascicle length was significantly longer in the middle (middle‐medial: 52.4 ± 6.1 mm, middle‐lateral: 52.0 ± 5.1 mm) compared to distal regions (distal‐medial: 41.0 ± 5.0 mm, distal‐lateral: 38.9 ± 3.6 mm, p < 0.001). The 2D pennation angle (angle relative to muscle surface) was significantly greater in distal than middle regions, and medial than lateral regions (middle‐medial: 26.6 ± 3.1°, middle‐lateral: 24.1 ± 2.3°, distal‐medial: 31.2 ± 3.6°, distal‐lateral: 29.2 ± 3.0°, p ≤ 0.017), while only a proximo‐distal difference was significant (p < 0.001) for 3D pennation angle (angle relative to line of action of muscle). These results clearly indicate fascicle's architectural variation in 3D. The magnitude of regional variation evaluated as standard deviation across regions differed considerably among individuals (4.0–10.7 mm for fascicle length, 0.9–5.0° for 2D pennation angle, and 3.0–8.8° for 3D pennation angle), which was positively correlated with the muscle volume normalized to body mass (r = 0.659–0.828, p ≤ 0.008). These findings indicate muscle‐size dependence of the variability of fascicle architecture.

Reliability and Validity of an Ultrasound-Based Protocol for Measurement of Quadriceps Muscle Thickness in Children

Introduction and aims: Accurate determination of skeletal muscle size is of great importance in multiple settings including resistance exercise, aging, disease, and disuse. Ultrasound (US) measurement of muscle thickness (MT) is a method of relatively high availability and low cost. The present study aims to evaluate a multisite ultrasonographic protocol for measurement of MT with respect to reproducibility and correlation to gold-standard measurements of muscle volume (MV) with magnetic resonance imaging (MRI) in children.

Material and methods: 15 children completed the study (11 ± 1 year, 41 ± 8 kg, 137 ± 35 cm). Following 20 min supine rest, two investigators performed US MT measurements of all four heads of the m. quadriceps femoris, at pre-determined sites. Subsequently, MRI scanning was performed and MV was estimated by manual contouring of individual muscle heads.

Results: Ultrasound measurement of MT had an intra-rater reliability of ICC = 0.985–0.998 (CI 95% = 0.972–0.998) and inter-rater reliability of ICC = 0.868–0.964 (CI 95% = 0.637–0.983). The US examinations took less than 15 min, per investigator. Muscle thickness of all individual quadriceps muscles correlated significantly with their corresponding MV as measured by MRI (overall r = 0.789, p < 0.001).

Conclusion: The results of this study indicate that US measurement of MT using a multisite protocol is a competitive alternative to MRI scanning, especially with respect to availability and time consumption. Therefore, US MT could allow for wider clinical and scientific implementation.

Effects of growth on muscle architecture of knee extensors

This study aimed to investigate the effects of growth on the muscle architecture of knee extensors. The present study included 123 male children and adolescents. The muscle thicknesses of the rectus femoris (RF) and vastus intermedius (VI), and pennation angles and fascicle lengths of RF were measured in three regions using ultrasonography technique at rest. The relative muscle thickness was calculated by dividing the absolute muscle thickness by body mass^1/3 . The years from age at peak height velocity were estimated for each participant, and used as a maturity index. The maturity index was significantly correlated with the relative muscle thicknesses of RF and VI in all regions. The slope of the relationship between the maturity index and the relative muscle thickness did not differ significantly between muscles within the same region or between regions within the individual muscles. The fascicle length and pennation angle of RF were significantly correlated with the absolute muscle thickness in all regions. In the proximal RF region, the coefficient of correlation between the muscle thickness and fascicle length was significantly greater than that between the muscle thickness and pennation angle. The present results showed that growth changes in muscle thickness were uniform between and within RF and VI. Our findings suggest that growth changes in the muscle thickness of RF depend on the increases in both pennation angle and fascicle length, but their contributions to the growth of muscle thickness differ among muscle regions.

Does Varying Resistance Exercises Promote Superior Muscle Hypertrophy and Strength Gains? A Systematic Review

ABSTRACT

Kassiano, W, Nunes, JP, Costa, B, Ribeiro, AS, Schoenfeld, BJ, and Cyrino, ES. Does varying resistance exercises promote superior muscle hypertrophy and strength gains? A systematic review. J Strength Cond Res 36(6): 1753-1762, 2022-Fitness professionals routinely employ a variety of resistance training exercises in program design as a strategy to enhance muscular adaptations. However, it remains uncertain whether such an approach offers advantages over a fixed-exercise selection. The objective of this review was to review the effects of exercise variation on muscle hypertrophy and strength. A search of the literature was conducted using PubMed/MEDLINE, Scopus, and Web of Science databases. Eight studies were identified as meeting inclusion criteria. The combined total sample of the studies was N = 241, comprising all young men. The methodological quality of included studies was considered "good" and "excellent" based on the Physiotherapy Evidence Database Scale. The available studies indicate that varying exercise selection can influence muscle hypertrophy and strength gains. Some degree of systematic variation seems to enhance regional hypertrophic adaptations and maximize dynamic strength, whereas excessive, random variation may compromise muscular gains. We conclude that exercise variation should be approached systematically with a focus on applied anatomical and biomechanical constructs; on the contrary, employing different exercises that provide a redundant stimulus, as well as excessive rotation of different exercises (i.e., high frequency of change), may actually hinder muscular adaptations.

Risk Factors for Quadriceps Muscle Strain Injuries in Sport: A Systematic Review

OBJECTIVE

To identify risk factors for quadriceps muscle strain injury in sport.

DESIGN

Risk factor systematic review.

LITERATURE SEARCH

A systematic search was conducted in the MEDLINECINAHL, Embase, AMED, AUSPORT, SPORTDiscus, PEDro, and Cochrane Library databases (from inception to September 2021).

STUDY SELECTION CRITERIA

Studies reporting prospective data to evaluate risk factors related to index and/or recurrent quadriceps muscle strain injury.

DATA SYNTHESIS

A risk-of-bias assessment (using a modified Quality in Prognosis Studies tool) was performed, and we used best-evidence synthesis to qualitatively synthesize the data to quantify relationships between risk factors and quadriceps muscle injury.

RESULTS

Sixteen studies were included, capturing 2408 quadriceps injuries in 11 719 athletes. Meta-analyses were not performed due to clinical heterogeneity. The dominant kicking leg (over 3154 individuals, 1055 injuries), a previous history of quadriceps muscle injury (6208 individuals, 975 injuries), and a recent history of hamstring strain (4087 individuals, 581 injuries) were intrinsic factors associated with quadriceps injury. Extrinsic factors relating to the preseason period and competitive match play increased quadriceps injury risk; participating at higher levels of competition decreased quadriceps injury risk. Age, weight, and flexibility (intrinsic factors) had no association with quadriceps injury.

CONCLUSION

Previous quadriceps injury, recent hamstring injury, the dominant kicking leg, and competitive match play were the strongest risk factors for future quadriceps muscle injury in sport. J Orthop Sports Phys Ther 2022;52(6):389-400. doi:10.2519/jospt.2022.10870.

Cross-education effect of 4-week high- or low-intensity static stretching intervention programs on passive properties of plantar flexors

This study aimed to compare the cross-education effect of unilateral stretching intervention programs with two different intensities (high- vs. low-intensity) on dorsiflexion range of motion (DF ROM), muscle stiffness, and muscle architecture following a 4-week stretching intervention. Twenty-eight healthy males were randomly allocated into two groups: a high-intensity static stretching (HI-SS) intervention group (n = 14; stretch intensity 6-7 out of 10) and a low-intensity static stretching (LI-SS) intervention group (n = 14; stretch intensity 0-1 out of 10). The participants were asked to stretch their dominant leg (prefer to kick a ball) for 4 weeks (3 × week for 3 × 60 s). Before and after the intervention, the non-trained leg passive properties (DF ROM, passive torque, and muscle stiffness) of the plantar flexors and the muscle architecture of the gastrocnemius medialis (muscle thickness, pennation angle, and fascicle length) were measured. Non-trained DF ROM and passive torque at DF ROM were significantly increased in the HI-SS group (p < 0.01, d = 0.64, 50.6%, and p = 0.044, d = 0.36, 18.2%, respectively), but not in the LI-SS group. Moreover, there were no significant changes in muscle stiffness and muscle architecture in both groups. For rehabilitation settings, a high-intensity SS intervention is required to increase the DF ROM of the non-trained limb. However, the increases in DF ROM seem to be related to changes in stretch tolerance and not to changes in muscle architecture or muscle stiffness.

Longing for a Longitudinal Proxy: Acutely Measured Surface EMG Amplitude is not a Validated Predictor of Muscle Hypertrophy

Surface electromyography amplitudes are commonly measured in acute sports and exercise science studies to make inferences about muscular strength, performance, and hypertrophic adaptations that may result from different exercises or exercise-related variables. Here, we discuss the presumptive logic and assumptions underlying these inferences, focusing on hypertrophic adaptations for simplicity's sake. We present counter-evidence for each of its premises and discuss evidence both for and against the logical conclusion. Given the limited evidence validating the amplitude of surface electromyograms as a predictor of longitudinal hypertrophic adaptations, coupled with its weak mechanistic foundation, we suggest that acute comparative studies that wish to assess stimulus potency be met with scrutiny.

Comparison Between High- and Low-Intensity Static Stretching Training Program on Active and Passive Properties of Plantar Flexors

The purpose of this study was to compare two static stretching (SS) training programs at high-intensity (HI-SS) and low-intensity (LI-SS) on passive and active properties of the plantar flexor muscles. Forty healthy young men were randomly allocated into three groups: HI-SS intervention group (n = 14), LI-SS intervention group (n = 13), and non-intervention control group (n = 13). An 11-point numerical scale (0–10; none to very painful stretching) was used to determine SS intensity. HI-SS and LI-SS stretched at 6–7 and 0–1 intensities, respectively, both in 3 sets of 60 s, 3×/week, for 4 weeks. Dorsiflexion range of motion (ROM), gastrocnemius muscle stiffness, muscle strength, drop jump height, and muscle architecture were assessed before and after SS training program. The HI-SS group improved more than LI-SS in ROM (40 vs. 15%) and decreased muscle stiffness (−57 vs. −24%), while no significant change was observed for muscle strength, drop jump height, and muscle architecture in both groups. The control group presented no significant change in any variable. Performing HI-SS is more effective than LI-SS for increasing ROM and decreasing muscle stiffness of plantar flexor muscles following a 4-week training period in young men. However, SS may not increase muscle strength or hypertrophy, regardless of the stretching discomfort intensity.

The role of exercise selection in regional Muscle Hypertrophy: A randomized controlled trial

There is emerging evidence suggesting that muscle growth is not homogeneous through the muscle. The aim of the present study was to analyse the role of exercise selection in regional hypertrophy. Two randomly allocated groups with equal training volume and intensity performed squats in the smith machine (SMTH group) or the leg extension exercise (LEG group). Growth in proximal, central and distal regions of the rectus femoris (RF) and vastus lateralis (VL) muscles, jump height and body composition were analysed. Results show that the three regions of RF grew significantly in the participants of the LEG group (p < 0.05), while only the central region of VL grew significantly in the SMTH group (p < 0.05). In summary, this study confirms that exercise selection plays a role in regional hypertrophy. Whilst there may be still other factors that determine how muscles grow, it seems that the chosen exercises may be responsible of the differences observed in this study.

Acute Effects of Dermal Suction on Passive Muscle and Joint Stiffness

The aim of the present study was to examine the acute effects of dermal suction on the passive mechanical properties of specific muscles and joints. Dermal suction was applied to the calves of 24 subjects. Passive plantar flexion torque was measured with the right knee fully extended and the right ankle positioned at 20°, 10°, 0°, and −10° angles, where 0° represents the ankle neutral position, and positive values correspond to the plantar flexion angle. The shear wave velocity (SWV) (m/s) of the medial gastrocnemius was measured in the same position using ultrasound shear wave elastography. The relationship between the joint angle and passive torque at each 10° angle was defined as passive joint stiffness (Nm/°). Passive muscle and joint stiffness were measured immediately before and after the dermal suction protocol. When the ankle joint was positioned at 20° (r = 0.53, P = 0.006), 10° (r = 0.43, P = 0.030), and −10° (r = 0.60, P = 0.001), the SWV was significantly higher after dermal suction than that before dermal suction. Regarding joint stiffness, we found no significant difference between the pre- and post-dermal suction values (partial η² = 0.093, P > 0.05). These findings suggest that dermal suction increases passive muscle stiffness and has a limited impact on passive joint stiffness.

Drop-Set Training Elicits Differential Increases in Non-Uniform Hypertrophy of the Quadriceps in Leg Extension Exercise

The study aimed to compare the effects of drop set resistance training (RT) versus traditional RT on markers of maximal muscle strength and regional hypertrophy of the quadriceps femoris. Sixteen recreationally active young men had one leg randomly assigned to the drop-set method (DS) and the other to training in a traditional manner (TRAD). Participants performed unilateral seated leg extensions using a periodized approach for eight weeks. Rectus femoris (RF) and vastus lateralis (VL) muscle thickness (MT), estimated one repetition maximum (RM) in the unilateral knee extension, and peak and average isokinetic knee extension torque at 60°/s angular velocity were measured pre- and post-study. Both conditions increased muscle thickness of the RF and VL from pre- to post-intervention. DS showed statistically greater increases in the RF at 30% and 50% of muscle length, whereas no MT differences were detected at 70% muscle length nor at any aspect of the VL. Both DS and TRAD increased estimated one RM from pre- to post-study (+34.6% versus +32.0%, respectively) with no between-condition differences noted. Both conditions showed similar increases in peak torque (DS: +21.7%; TRAD: +22.5%) and average torque (DS: +23.6%; TRAD: +22.5%) from pre- to post-study. Our findings indicate a potential benefit of the drop-set method for inducing non-uniform hypertrophic gains in the RF muscle pursuant to leg extension training. The strategy did not promote an advantage in improving hypertrophy of the VL, nor in strength-related measures, compared to traditional training.

Skeletal Muscle Quality: A Biomarker for Assessing Physical Performance Capabilities in Young Populations

Muscle quality (MQ), defined as the amount of strength and/or power per unit of muscle mass, is a novel index of functional capacity that is increasingly relied upon as a critical biomarker of muscle health in low functioning aging and pathophysiological adult populations. Understanding the phenotypical attributes of MQ and how to use it as an assessment tool to explore the efficacy of resistance exercise training interventions that prioritize functional enhancement over increases in muscle size may have implications for populations beyond compromised adults, including healthy young adults who routinely perform physically demanding tasks for competitive or occupational purposes. However, MQ has received far less attention in healthy young populations than it has in compromised adults. Researchers and practitioners continue to rely upon static measures of lean mass or isolated measures of strength and power, rather than using MQ, to assess integrated functional responses to resistance exercise training and physical stress. Therefore, this review will critically examine MQ and the evidence base to establish this metric as a practical and important biomarker for functional capacity and performance in healthy, young populations. Interventions that enhance MQ, such as high-intensity stretch shortening contraction resistance exercise training, will be highlighted. Finally, we will explore the potential to leverage MQ as a practical assessment tool to evaluate function and enhance performance in young populations in non-traditional research settings.

Rest-pause and drop-set training elicit similar strength and hypertrophy adaptations compared to traditional sets in resistance-trained males

The present paper aimed to compare the effect of drop-set (DS) and rest-pause (RP) systems versus traditional resistance training (TRT) with equalized total training volume on maximum dynamic strength (1RM) and thigh muscle thickness (MT).Twenty-eight resistance-trained males were randomly assigned to either RP (n = 10), DS (n = 9) or TRT (n = 9) protocols performed twice a week for 8 weeks. 1RM and MT of the proximal, middle and distal portions of the lateral thigh were assessed at baseline and post intervention.A significant time x group interaction was observed for 1RM (P = 0.025) in the barbell back squat after 8-weeks. Post hoc comparisons revealed that RP promoted higher 1RM than TRT (P = 0.001); no statistical differences in strength were observed between the other conditions. A significant main effect of time was revealed for MT at the proximal (P = 0.0001) and middle (P = 0.0001) aspects of the lateral thigh for all training groups; however, the distal portion did not show a time effect (P = 0.190). There were no between-group interactions for MT. Our findings suggest that RP promotes slightly superior strength-related improvements compared to TRT, but hypertrophic adaptations are similar between conditions. Novelty bullets • Rest-pause elicited a slightly superior benefit for strength adaptations compared to traditional resistance training. • Resistance training systems do not promote superior hypertrophic adaptations when total training volume is equalized. • Muscle thickness in distal portion of thigh are similar to baseline. Although modest, effect sizes tended to favor rest-pause.

Investigation of the association between human fascia lata thickness and its neighboring tissues' morphology and function using B-mode ultrasonography

The fascia lata is a membrane tissue which envelopes all thigh muscles and connects with the subcutaneous adipose tissues through loose connective tissues. It is presumable that the morphology of the fascia lata is strongly affected by the unique properties of underlying thigh muscles and subcutaneous adipose tissues. We aimed to investigate the relationships between characteristics of the fascia lata and adjoining adipose tissues and underlying muscles. Twenty healthy people were recruited (25 ± 3 years, 167.1 ± 8.5 cm, 62.5 ± 13.2 kg). The thickness of the skeletal muscles (rectus femoris, vastus lateralis, biceps femoris, and semitendinosus), and their overlying fascia lata and subcutaneous adipose tissues were measured by B‐mode ultrasonography. Isometric knee extension and flexion torque during maximal voluntary contraction were also tested. The fascia lata thickness demonstrated site‐dependent differences (vastus lateralis: 0.91 ± 0.20 mm > rectus femoris, biceps femoris, and semitendinosus: 0.56–0.69 mm, p < 0.01). Furthermore, there were large individual variations in the fascia lata thickness even in the same region of the thigh. The fascia lata showed positive simple correlations with height (rectus femoris: r = 0.39 p = 0.01, semitendinosus: r = 0.37 p < 0.05), body mass (rectus femoris: r = 0.59, p < 0.01, vastus lateralis: r = 0.47, p < 0.01, semitendinosus: r = 0.55, p < 0.01), corresponding muscle thickness (rectus femoris: r = 0.39, p < 0.05, semitendinosus: r = 0.74, p < 0.01) and knee extension (rectus femoris: r = 0.52, p < 0.01, vastus lateralis: r = 0.40, p < 0.01) and flexion (semitendinosus: r = 0.41, p < 0.01) torques. After adjusting for the influence of height and/or body mass, the fascia lata thickness showed a partial correlation only with the skeletal muscle thickness at the semitendinosus (r = 0.61, p < 0.01). The present study revealed that the fascia lata has site‐specific differences of the thickness, which positively correlates with the underlying muscle thickness and corresponding joint torque. Furthermore, the fascia lata over the semitendinosus is associated with the underlying muscle characteristics independent of the physical constitution. It is assumed that the fascia lata has the plasticity and changes its thickness, which likely corresponds to the morphology of the neighboring tissues and underlying muscle function.

The fascia lata showed individual differences of its thickness which was positively correlated with its underlying muscle thickness and/or strength. Especially, the fascia lata over the ST reflects the underlying muscle characteristics regardless of the physical constitution.

Novel Insights Into Biarticular Muscle Actions Gained From High-Density Electromyogram

Biarticular muscles have traditionally been considered to exhibit homogeneous neuromuscular activation. The regional activation of biarticular muscles, as revealed from high-density surface electromyograms, seems however to discredit this notion. We thus hypothesize the regional activation of biarticular muscles may contribute to different actions about the joints they span. We then discuss the mechanistic basis and methodological implications underpinning our hypothesis.

The Human Muscle Size and Strength Relationship: Effects of Architecture, Muscle Force, and Measurement Location

PURPOSE

This study aimed to determine the best muscle size index of muscle strength by establishing if incorporating muscle architecture measurements improved the human muscle size-strength relationship. The influence of calculating muscle force, and the location of anatomical cross-sectional area (ACSA) measurements on this relationship were also examined.

METHODS

Fifty-two recreationally active males completed unilateral isometric knee extension strength assessments and MRI scans of the dominant thigh and knee to determine quadriceps femoris (QF) size variables (ACSA along the length of the femur, maximum ACSA [ACSAMAX] and volume [VOL]) and patellar tendon moment arm. Ultrasound images (2 sites per constituent muscle) were analyzed to quantify muscle architecture (fascicle length, pennation angle), and when combined with VOL (from MRI), facilitated calculation of QF effective PCSA (EFFPCSA) as potentially the best muscle size determinant of strength. Muscle force was calculated by dividing maximum voluntary torque (MVT) by the moment arm and addition of antagonist torque (derived from hamstring EMG).

RESULTS

The associations of EFFPCSA (r=0.685), ACSAMAX (r=0.697), or VOL (r=0.773) with strength did not differ, although qualitatively VOL explained 59.8% of the variance in strength, ~11-13% greater than EFFPCSA or ACSAMAX. All muscle size variables had weaker associations with muscle force than MVT. The association of strength-ACSA at 65% of femur length (r=0.719) was greater than for ACSA measured between 10-55% and 75-90% (r=-0.042-0.633) of femur length.

CONCLUSIONS

In conclusion, using contemporary methods to assess muscle architecture and calculate EFFPCSA did not enhance the muscle strength-size association. For understanding/monitoring muscle size, the major determinant of strength, these findings support the assessment of muscle volume, that is independent of architecture measurements, and was most highly correlated to strength.

Gluteus and posterior thigh muscle sizes in sprinters: Their distributions along muscle length

Muscle hypertrophy can occur non-uniformly in athletes who repetitively perform particular movements, presumably leading to a unique muscle size distribution along the length. The present study aimed to examine if sprinters have unique size distributions within the gluteus and posterior thigh muscles. Nineteen male sprinters and 20 untrained males participated in the present study. T1-weighted magnetic resonance images of the hips and right thigh were obtained in order to determine whole and regional (proximal, middle, and distal) volumes of the gluteus maximus and individual posterior thigh muscles. The results showed that the volumes of all the examined muscles relative to body mass were significantly larger in sprinters than in untrained males (all P < 0.001, d = 1.40-3.29). Moreover, the magnitude of the difference in relative volume between sprinters and untrained males was different between the regions within the gluteus maximus (P = 0.048, partial η² = 0.187), semitendinosus (P = 0.004, partial η² = 0.331), and adductor magnus (P = 0.007, partial η² = 0.322), but not within the other posterior thigh muscles (P = 0.091-0.555, partial η² = 0.025-0.176). The magnitude of the difference in relative volume between the sprinters and untrained males was greatest in the distal regions within the gluteus maximus and semitendinosus, while the proximal region within the adductor magnus. These findings indicate that sprinters have unique size distributions within the gluteus maximus, semitendinosus, and adductor magnus, which may be attributed to their competitive and training activities. HighlightsSprinters showed larger gluteus maximus and individual posterior thigh muscles than untrained males.The magnitude of difference varied within the gluteus maximus, semitendinosus, and adductor magnus.The greatest difference was found in distal regions within the gluteus maximus and semitendinosus, while proximal region within the adductor magnus.

Equating Resistance-Training Volume Between Programs Focused on Muscle Hypertrophy

Calculating resistance-training volume in programs focused on muscle hypertrophy is an attempt to quantify the external workload carried out, then to estimate the dose of stimulus imposed on targeted muscles. The volume is usually expressed in some variables that directly affected the total training work, such as the number of sets, repetitions, and volume-load. These variables are used to try to quantify the training work easily, for the subsequent organization and prescription of training programs. One of the main uses of measures of volume quantification is seen in studies in which the purpose is to compare the effects of different training protocols on muscle growth in a volume-equated format. However, it seems that not all measures of volume are always appropriate for equating training protocols. In the current paper, it is discussed what training volume is and the potentials and shortcomings of each one of the most common ways to equate it between groups depending on the independent variable to be compared (e.g., weekly frequency, intensity of load, and advanced techniques).

Selection of Resistance Exercises for Older Individuals: The Forgotten Variable

Resistance training has been widely recommended as a strategy to enhance the functional autonomy and quality of life in older individuals. Among the variables that comprise a training session, the selection of exercises stands out as an important consideration for the elderly. Although a wide range of resistance exercise options exists, current guidelines generally do not indicate which exercises should be included and which muscles should be prioritized when prescribing training for older individuals. Therefore, given the lack of evidence-based information on the topic, this paper endeavors to establish recommendations to help guide the prescription of resistance exercises for older adults.

Effects of Adding Inter-Set Static Stretching to Flywheel Resistance Training on Flexibility, Muscular Strength, and Regional Hypertrophy in Young Men

Performing static stretching (SS) during resistance training (RT) rest periods is posited to potentiate muscular adaptations, but the literature is scarce on the topic. Thus, the purpose of this study was to investigate the effects of adding inter-set SS to a lower-limb flywheel RT program on joint flexibility, muscular strength, and regional hypertrophy. Sixteen untrained male adults (21 ± 1 y) completed the study, where they performed progressive flywheel bilateral squatting twice a week for 5 weeks. One leg of each participant was randomly allocated to perform SS during the inter-set rest period (RT+SS), while the other leg served as control (RT only). Before and after the intervention, knee flexion range of motion; knee extension isometric, concentric, and eccentric peak torque; 1-repetition maximum; and muscle thickness of the lower-limb muscles were assessed. Following the training period, additional effects were observed for the inter-set SS side on increasing joint flexibility (p < 0.05), whereas the average increase in strength measures was 5.3% for the control side, and 10.1% for the inter-set SS side, however, SS intervention induced significantly greater gains only for knee extension isometric strength, but not for dynamic 1-RM, concentric, and eccentric tests. Hamstrings and gluteus maximus did not hypertrophy with training; increases quadriceps muscle thickness depended on the site/portion analyzed, but no significant difference was observed between legs (average: RT = 7.3%, RT+SS = 8.0%). The results indicate that adding inter-set SS to RT may provide large gains in flexibility, slightly benefits for muscular strength (especially for isometric action), but do not impact muscle hypertrophy in untrained young men.

Hamstring Muscle Volume as an Indicator of Sprint Performance

ABSTRACT

Nuell, S, Illera-Domínguez, V, Carmona, G, Macadam, P, Lloret, M, Padullés, JM, Alomar, X, and Cadefau, JA. Hamstring muscle volume as an indicator of sprint performance. J Strength Cond Res 35(4): 902-909, 2021-This study aimed to compare mechanical properties and performance during sprinting, as well as thigh muscle volumes (MVs), between national-level sprinters and physically active males. In addition, the relationships between thigh MVs and sprint mechanical properties and performance were investigated. Seven male sprinters and 9 actives performed maximal-effort 40-m sprints. Instantaneous velocity was measured by radar to obtain theoretical maximum force (F0), the theoretical maximum velocity (V0), and the maximum power (Pmax). For MV assessment, series of cross-sectional images of each subject's thigh were obtained by magnetic resonance imaging for each of the quadriceps and hamstring muscles and the adductor muscle group. Sprinters were faster over 10 m (7%, effect size [ES] = 2.12, p < 0.01) and 40 m (11%, ES = 3.68, p < 0.01), with significantly higher V0 (20%, ES = 4.53, p < 0.01) and Pmax (28%, ES = 3.04, p < 0.01). Sprinters had larger quadriceps (14%, ES = 1.12, p < 0.05), adductors (23%, ES = 1.33, p < 0.05), and hamstrings (32%, ES = 2.11, p < 0.01) MVs than actives. Hamstrings MV correlated strongly with 40-m sprint time (r = -0.670, p < 0.01) and V0 (r = 0.757, p < 0.01), and moderately with Pmax (r = 0.559, p < 0.05). Sprinters were significantly faster and had greater V0 and Pmax than active males. Larger MVs were found in sprinters' thighs, especially in the hamstring musculature, and strong correlations were found between hamstring MV and sprint mechanical properties and sprint performance.

Effects of a high-volume static stretching programme on plantar-flexor muscle strength and architecture

PURPOSE

Static stretching (SS) is performed in various settings, but there is no consensus about the effects of SS programmes on changes in muscle morphofunction. This study aimed to investigate the effects of a high-volume SS programme on muscle strength and architecture.

METHODS

Sixteen healthy young male adults participated, and the dominant leg was defined as the intervention side, with the non-dominant leg as the control side. Stretching exercises were performed two times per week (6 sets of 5 min, totally 30 min per session,) for 5-week using a stretching board under the supervision of the research team. Before and after SS intervention programme, plantar-flexor strength (maximum voluntary isometric contraction, MVC-ISO; maximum voluntary concentric contraction, MVC-CON) and architecture (muscle thickness, pennation angle, and fascicle length) were measured via dynamometer and ultrasound, respectively.

RESULTS

Following the SS-training programme, significant increases were observed for stretching side in MVIC-ISO at neutral ankle position (p = 0.02, d = 0.31, Δ = 6.4 ± 9.9%) and MVC-CON at 120°/s (p = 0.02, d = 0.30, Δ = 7.8 ± 9.1%), with no significant change on the control side. There was no significant change in any measure of muscle architecture for both intervention and control sides.

CONCLUSION

Five-week high-volume SS induced positive changes on some measures of muscle strength but not hypertrophy of plantar-flexor muscles. Even with a volume much greater than already tested, the low strain offered by the SS per set seems be insufficient to induce architectural changes on skeletal muscle.

Inhomogeneous and anisotropic mechanical properties of the triceps surae muscles and aponeuroses in vivo during submaximal muscle contraction

This study aimed to identify characteristics of the triceps surae muscles and aponeuroses stiffness in vivo, during graded isometric submaximal plantarflexion efforts. A total of twelve healthy male subjects (age: 27 ± 4 years) participated and were required to stay at rest (0% MVC) and perform isometric submaximal plantar flexion contractions (20%, 40%, 60% of MVC) on a dynamometer. Young's modulus of triceps surae muscles and the adjoining aponeuroses between gastrocnemii and soleus at the proximal and distal sites were obtained in the longitudinal direction (along muscle's line of action) during at rest and submaximal plantar flexions. Additionally, Young's modulus of adjoining aponeuroses in the transverse direction at the distal sites was also calculated. Young's modulus of LG (lateral gastrocnemius), SOL-lat (lateral part of soleus) and LPS (superficial aponeurosis of LG) at the proximal site showed significant (p < 0.001) graded increase response to the submaximal contraction levels. Besides, in the lateral side, significant differences in the Young's modulus of aponeuroses were observed between longitudinal and transverse directions at rest and during contractions (p < 0.002). Changes of aponeuroses length were significantly correlated with Young's modulus changes of the proximal gastrocnemii muscle bellies (r = 0.43-0.45, p = 0.006-0.008) and superficial aponeuroses (r = 0.49-0.60, p < 0.002). The results further indicate that the triceps surae muscles and aponeuroses showed inhomogeneous and anisotropic mechanical properties during submaximal muscle contractions, and the stiffening effect of muscle belly possibly make influence on the mechanical properties of aponeuroses during muscle contractions, especially for the lateral gastrocnemius.

Association between medial gastrocnemius muscle-tendon unit architecture and ankle dorsiflexion range of motion with and without consideration of slack angle

Joint flexibility is theoretically considered to associate with muscle-tendon unit (MTU) architecture. However, this potential association has not been experimentally demonstrated in humans in vivo. We aimed to identify whether and how MTU architectural parameters are associated with joint range of motion (RoM), with a special emphasis on slack angle. The fascicle length, pennation angle, tendinous tissue length, MTU length, and shear modulus of the medial gastrocnemius (MG) were assessed during passive ankle dorsiflexion using ultrasound shear wave elastography in 17 healthy males. During passive dorsiflexion task, the ankle joint was rotated from 40° plantar flexion to the maximal dorsiflexion joint angle at which each subject started experiencing pain. From the ankle joint angle-shear modulus relationship, the angle at which shear modulus began to rise (slack angle) was calculated. Two dorsiflexion RoMs were determined as follows; 1) range from the anatomical position to maximal angle (RoM_anat-max) and 2) range from the MG slack angle to maximal angle (RoM_slack-max). The MTU architectural parameters were analyzed at the anatomical position and MG slack angle. The resolved fascicle length (fascicle length × cosine of pennation angle) and ratios of resolved fascicle or tendinous tissue length to MTU length measured at the MG slack angle significantly correlated with the RoM_slack-max (r = 0.491, 0.506, and -0.506, respectively). Any MTU architectural parameters assessed at the anatomical position did not correlate with RoM_anat-max or RoM_slack-max. These results indicate that MTUs with long fascicle and short tendinous tissue are advantageous for joint flexibility. However, this association cannot be found unless MTU architecture and joint RoM are assessed with consideration of muscle slack.

Does Varying Repetition Tempo in a Single-Joint Lower Body Exercise Augment Muscle Size and Strength in Resistance-Trained Men?

Pearson, J, Wadhi, T, Barakat, C, Aube, D, Schoenfeld, BJ, Andersen, JC, Barroso, R, Ugrinowitsch, C, and De Souza, EO. Does varying repetition tempo in a single-joint lower body exercise augment muscle size and strength in resistance-trained men? J Strength Cond Res XX(X): 000-000, 2021-This study compared the effects of FAST and SLOW eccentric repetition tempo in a single exercise volume-matched intervention on muscle thickness (MT) and strength in resistance-trained men. Using a within-subject design, 13 subjects had each leg randomly assigned to SLOW (1-0-3) or FAST (1-0-1) repetition tempo. Subjects underwent an 8-week strength-training (ST) intervention performed twice weekly. Unilateral leg-extension one repetition-maximum (1RM) and anterior thigh MT at the proximal (MTP) and distal (MTD) portions were assessed via ultrasound imaging at baseline and after 8 weeks of RT. Rating of perceived exertion (RPE) assessments of the training sessions (i.e., 16 per leg) were averaged for further analysis. Both legs similarly increased MTP (estimated differences: FAST: 0.24 cm, 3.6%; SLOW: 0.20 cm, 3.1%). However, for MTD, analysis of covariance analysis showed a leg effect (p = 0.02) in which absolute pre-to-post change was greater in FAST compared with SLOW (estimated differences: FAST 0.23 cm, 5.5%; SLOW: 0.13 cm, 2.2%). For 1RM, both legs similarly increased maximum strength (estimated differences: FAST: 9.1 kg, 17.0%; SLOW: 10.4 kg, 22.1%, p <= 0.0001). The SLOW group had a higher RPE than FAST (8.59 vs. 7.98, p = 0.002). Despite differences in RPE, our results indicate that both repetition tempos produced similar muscular adaptations. However, they also suggest that the FAST tempo may provide a small hypertrophic advantage at the distal quadriceps. From a practical standpoint, strength and conditioning professionals may implement a FAST tempo at least in one single-joint exercise during an 8-week training period to enhance regional hypertrophic adaptations in trained individuals.

Muscle architecture and morphology as determinants of explosive strength

PURPOSE

Neural drive and contractile properties are well-defined physiological determinants of explosive strength, the influence of muscle architecture and related morphology on explosive strength is poorly understood. The aim of this study was to examine the relationships between Quadriceps muscle architecture (pennation angle [Θ_P] and fascicle length [F_L]) and size (e.g., volume; Q_VOL), as well as patellar tendon moment arm (PT_MA) with voluntary and evoked explosive knee extension torque in 53 recreationally active young men.

METHOD

Following familiarisation, explosive voluntary torque at 50 ms intervals from torque onset (T₅₀, T₁₀₀, T₁₅₀), evoked octet at 50 ms (8 pulses at 300-Hz; evoked T₅₀), as well as maximum voluntary torque, were assessed on two occasions with isometric dynamometry. B-mode ultrasound was used to assess Θ_P and F_L at ten sites throughout the quadriceps (2-3 sites) per constituent muscle. Muscle size (Q_VOL) and PT_MA were quantified using 1.5 T MRI.

RESULT

There were no relationships with absolute early phase explosive voluntary torque (≤ 50 ms), but θ_P (weak), Q_VOL (moderate to strong) and PT_MA (weak) were related to late phase explosive voluntary torque (≥ 100 ms). Regression analysis revealed only Q_VOL was an independent variable contributing to the variance in T₁₀₀ (34%) and T₁₅₀ (54%). Evoked T₅₀ was also related to Q_VOL and θ_P. When explosive strength was expressed relative to MVT there were no relationships observed.

CONCLUSION

It is likely that the weak associations of θ_P and PT_MA with late phase explosive voluntary torque was via their association with MVT/Q_VOL rather than as a direct determinant.

Does Performing Different Resistance Exercises for the Same Muscle Group Induce Non-homogeneous Hypertrophy?

The study aimed to compare the effect of performing the same or different exercises for a muscle group on resistance training (RT) sessions on muscle hypertrophy at different sites along muscle length. Twenty-two detrained men (23.3±4.1 years) were randomly allocated to the following groups: a group that performed the same exercises in all training sessions (N-VAR=11) or one that varied the exercises for the same muscle groups (VAR=11). All were submitted to 3 weekly sessions for nine weeks. Muscle thickness was assessed at the proximal, middle, and distal sites of the lateral and anterior thigh, elbow flexors, and extensors by B-mode ultrasound. The VAR group significantly increased all the sites analyzed (P<0.05). Furthermore, the proximal site of the lateral thigh showed a larger relative increase when compared to the middle site (P<0.05). In contrast, the N-VAR group were not revealed significant improvements only for the middle site of the lateral thigh and the proximal site of the elbow flexors (P>0.05). Our results suggest that to perform different resistance exercises can induce hypertrophy of all sites assessed in detrained young men.

Resistance training exercise selection: efficiency, safety and comfort analysis method

Abstract Manipulation of resistance training variables has been shown to have a substantial effect on muscular adaptations. A major variable in this process is exercise selection. In addition to the effectiveness of a given exercise to recruit the target muscle groups, safety considerations and individual comfort during execution of a lift should be considered. The correct biomechanics of the chosen exercise will assist in promoting desired muscle adaptations, while proper safety procedures will reduce risk of injury. Lifting comfort will facilitate enjoyment and foster adherence to the program. Therefore, the purpose of this paper was to offer guidelines for selection of resistance training exercises based on the Efficiency, Safety, and Comfort Analysis Method (ESCAM).

Assessment methods of vastus lateralis muscle architecture using panoramic ultrasound: a new approach, test-retest reliability and measurement error

Abstract Extended-field-of-view ultrasonography is a valid alternative to determine the dimensions of the skeletal striated muscle; however, some factors may influence the final measurement. The aim of this study was to determine the test-retest reliability and measurement error of vastus lateralis muscle architecture variables through internal anatomical landmarks and to compare three fixed determined points using extended-field-of-view ultrasonography. Twelve young (24 ± 6 years) adult university male students participated in the study. Images were obtained through extended-field-of-view ultrasonography of the vastus lateralis muscle. Measurements were made for muscle thickness (MT), fascicle length (FL), and fascicle pennation angle (FA) using a method that identifies internal anatomical landmarks. MT was also measured at predetermined distances of 2 cm proximal, 6 cm proximal, and 2 cm distal. One-way ANOVA with repeated measures did not identify any test-retest significant differences for all variables measured. Typical measurement error in centimeters (cm) or degrees (º), coefficient of variation in percentage (%) and intraclass correlation coefficient were MT = 0.07 cm, 2.93%, 0.964; FL = 0.31 cm, 2.89%, 0.947; FA = 0.92°, 4.08%, 0.942; MT 2 cm proximal = 0.10 cm, 3.77%, 0.910; MT 6 cm proximal = 0.27 cm, 9.66%, 0.576; MT 2 cm distal = 0.35 cm, 19.76%, 0.564. MT, FL and FA showed high reliability and low measurement error. Internal anatomical landmarks proved to be more reliable and presented smaller measurement errors when compared to the predetermined distances method.

One-repetition maximum can be estimated with a handheld dynamometer and circumference in community-dwelling older adults

[Purpose] One-repetition maximum is an essential statistic for physical therapists and coaches in rehabilitation and athletic settings. In a previous study, we showed that one-repetition maximum of the knee extensor could be predicted more accurately with the combination of maximal voluntary isometric contraction strength, as measured by a handheld dynamometer, muscle thickness, and thigh circumference, in young adults. However, there has been no study in older adults investigating the relationship between one-repetition maximum and maximal voluntary isometric contraction strength, or muscle thickness, and thigh circumference. Therefore, the aim of this study was to investigate the relationship between one-repetition maximum and maximal voluntary isometric contraction strength, or muscle thickness, and thigh circumference in older adults. [Participants and Methods] Twenty-eight older community-dwelling adults (18 males and 10 females) participated in this study. Muscle strength of the knee extensor was measured using one-repetition maximum and maximal voluntary isometric contraction strength. In addition, muscle thicknesses of the refutes femoris and the vastus intermedius, and thigh circumference were measured using ultrasonography and measuring tape, respectively. [Results] Stepwise regression analysis revealed that body mass, gender, thigh circumference at 15 cm above the patella, and maximal voluntary isometric contraction strength were significant and independent determinants (R²=0.868). [Conclusion] One-repetition maximum could be predicted more accurately using a combination of maximal voluntary isometric contraction strength, as measured with a handheld dynamometer, and thigh circumference in older adults.

Comparison of the relative muscle volume of triceps surae among sprinters, runners, and untrained participants

Muscle hypertrophy is considered more prominent in fast‐twitch than in slow‐twitch muscles. This leads to the hypothesis that the relative muscle volume of the medial gastrocnemius (MG) and lateral gastrocnemius (LG) becomes larger than that of the soleus (SOL) in highly trained participants because MG and LG include more fast‐twitch muscles than SOL. Thus, we compared relative muscle volume among highly trained sprinters, long‐distance runners, and untrained participants to examine whether the above hypothesis is correct. Magnetic resonance imaging was used to calculate the muscle volume of MG, LG, and SOL from 126 participants. The total muscle volume of the three muscles and the relative muscle volume of each muscle with respect to the total muscle volume were calculated. The total muscle volume was significantly larger in the sprinters than in the long‐distance runners and untrained participants. The relative muscle volume of MG was significantly larger in the sprinters than in the long‐distance runners and untrained participants and that of SOL was significantly smaller in the sprinters than in the long‐distance runners and untrained participants. These results indicate that the relative muscle volume can vary among participants, possibly due to fiber type‐dependent muscle hypertrophy.

Inertial flywheel knee- and hip-dominant hamstring strength exercises in professional soccer players: Muscle use and velocity-based (mechanical) eccentric overload

The primary aim of the present study was to analyze mechanical responses during inertial knee- and hip-dominant hamstring strengthening exercises (flywheel leg-curl and hip-extension in conic-pulley), and the secondary aim was to measure and compare regional muscle use using functional magnetic resonance imaging. Mean power, peak power, mean velocity, peak velocity and time in the concentric (CON) and eccentric (ECC) phases were measured. The transverse relaxation time (T2) shift from pre- to post-exercise were calculated for the biceps femoris long (BFl) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. Peak and mean power in flywheel leg-curl were higher during the CON than the ECC phase (p<0.01). ECC peak power was higher than CON phase (p<0.01) in conic-pulley hip-extension exercise, while mean power was higher during the CON than ECC phase (p<0.01). Flywheel leg-curl showed a higher T2 values in ST and BFs and BFl (p<0.05), while the conic-pulley hip-extension had a higher T2 values in the proximal region of the ST and BFl (p<0.05). In conclusion, ECC overload was only observed in peak power during the conic-pulley hip-extension exercise. Flywheel leg-curl involved a greater overall use of the 4 muscle bellies, more specifically in the ST and BFs, with a selective augmented activity (compared with the conic-pulley) in the 3 regions of the BFs, while conic-pulley hip-extension exercise selectively targeted the proximal and medial regions of the BFl. Physiotherapists and strength and conditioning coaches should consider this when optimizing the training and recovery process for hamstring muscles, especially after injury.