A New Portable Device to Reliably Measure Maximal Strength and Rate of Force Development of Hip Adduction and Abduction.

ABSTRACT: Gonçalves, BM, Mesquita, RNO, Tavares, F, Brito, J, Correia, P, Santos, P, and Mil-Homens, P. A new portable device to reliably measure maximal strength and rate of force development of hip adduction and abduction. J Strength Cond Res 36(9): 2465-2471, 2022-Groin injuries are a major issue in sports involving kicking or quick changes of direction. Decreased hip adduction and abduction strength have been indicated as one of the main risk factors for groin injury. The methods currently available to measure hip adduction and abduction strength are reliable but highly dependent on the evaluator skills. Furthermore, several studies have reported the reliability of maximal strength (MVIC), but very few studies investigated the reliability of explosive strength (RFD), a parameter that has been previously shown to have a higher functional value. The aim of the current investigation was to assess the reliability of a user-independent portable dynamometer that concurrently measures MVIC and RFD. Twenty-five healthy young subjects performed maximal isometric hip adduction and abduction in both sitting and supine positions. Measurements occurred in 2 different days separated by 48-72 hours. Test-retest reliability was calculated for both MVIC and RFD. Both MVIC and RFD showed good relative reliability (intraclass correlation coefficient = 0.77-0.98) with no differences between positions or muscle actions. Measurement error was similar between positions for MVIC in both hip adduction and abduction. Measurements of RFD showed higher reliability using a time window of at least 0-100 milliseconds, and lower measurement error was observed in sitting for adduction and in supine for abduction. This study shows that portable dynamometry can be used to concurrently measure hip adduction and abduction maximal and explosive strength, with levels of reliability that are similar to previously described methods.

Contralateral training effects of low-intensity blood-flow restricted and high-intensity unilateral resistance training.

PURPOSE: Determine whether unilateral low-intensity blood-flow restricted (LIBFR) exercise is as effective as high-intensity (HI) resistance training for improving contralateral muscle strength. METHODS: Thirty healthy adults (20-30 years) were randomly allocated to the following dynamic plantar-flexion training interventions: HI [75% of one-repetition maximum (1RM), 4 sets, 10 reps] and LIBFR [20% of 1RM, 4 sets, 30 + 15 + 15 + 15 reps]. Evoked V-wave and H-reflex recruitment curves, as well as maximal voluntary contraction (MVC) and panoramic ultrasound assessments of the trained and untrained soleus muscles were obtained pre-training, post-4 weeks of training and post-4 weeks of detraining. RESULTS: Both interventions failed to increase contralateral MVC and muscle cross-sectional area (CSA). Yet, contralateral rate of torque development (RTD) was enhanced by both regimens (12-26%) and this was accompanied by heightened soleus EMG within the first milliseconds of the rising torque-time curve (14-22%; p < 0.05). These improvements were dissipated after detraining. Contralateral adaptations were not accompanied by changes in V-wave or H-reflex excitability. Conversely, LIBFR and HI elicited a similar magnitude of ipsilateral increase in MVC, RTD and CSA post-training (10-18%). Improvements in V-wave amplitude and soleus EMG were limited to the trained leg assigned to LIBFR training (p < 0.05). While gains in strength and CSA remained preserved post-4 weeks of detraining, this did not occur with RTD. CONCLUSION: Since gains in RTD were similar between interventions, our findings indicate that both training regimens can be used interchangeably for improving contralateral rapid torque production. Ultimately, this may be beneficial in circumstances of limb immobilization after injury or surgery.

Effects of Four Different Velocity-Based Training Programming Models on Strength Gains and Physical Performance.

ABSTRACT: Riscart-López, J, Rendeiro-Pinho, G, Mil-Homens, P, Costa, RS-d, Loturco, I, Pareja-Blanco, F, and León-Prados, JA. Effects of Four different velocity-based training programming models on strength gains and physical performance. J Strength Cond Res 35(3): 596-603, 2021-The aim of this study was to compare the effects of 4 velocity-based training (VBT) programming models (linear programming [LP], undulating programming [UP], reverse programming [RP], and constant programming [CP]) on the physical performance of moderately strength-trained men. Forty-three young (age: 22.9 ± 4.8 years; body mass [BM]: 71.7 ± 7.6; full squat [SQ] relative strength 1.32 ± 0.29) subjects were randomly assigned to LP (gradually increase training intensity and decrease volume), UP (volume and intensity increase or decrease repeatedly), RP (gradually increases volume and decrease intensity), and CP (maintains constant volume and intensity) groups and followed an 8-week VBT intervention using the SQ exercise and monitoring movement velocity for every repetition. All groups trained with similar relative average intensity (67.5% 1 repetition maximum [1RM]), magnitude of velocity loss within the set (20%), number of sets (3), and interset recoveries (4 minutes) throughout the training program. Pre-training and post-training measurements included predicted SQ (1RM), average velocity attained for all loads common to pre-tests and post-tests (AV), average velocity for those loads that were moved faster (AV > 1) and slower (AV < 1) than 1 m·s-1 at pre-tests, countermovement jump height (CMJ), and 20-m sprint time (T20). No significant group × time interactions were observed for any of the variables analyzed. All groups obtained similar increases (shown in effect size values) in 1RM strength (LP: 0.88; UP: 0.54; RP: 0.62; CP: 0.51), velocity-load-related variables (LP: 0.74-4.15; UP: 0.46-5.04; RP: 0.36-3.71; CP: 0.74-3.23), CMJ height (LP: 0.35; UP: 0.53; RP: 0.49; CP: 0.34), and sprint performance (LP: 0.34; UP: 0.35; RP: 0.32; CP: 0.30). These results suggest that different VBT programming models induced similar physical performance gains in moderately strength-trained subjects.

Blood Flow Restriction Alters Motor Unit Behavior During Resistance Exercise.

We aimed to determine whether blood flow restriction (BFR) alters the characteristics of individual motor units during low-intensity (LI) exercise. Eight men (26.0±3.8 yrs) performed 5 sets of 15 knee extensions at 20% of one-repetition maximum (with and without BFR). Maximal isometric voluntary contractions (MVC) were performed before and after exercise to quantify force decrement. Submaximal isometric voluntary contractions were additionally performed for 18 s, matching trapezoidal target-force trajectories at 40% pre-MVC. EMG activity was recorded from the vastus lateralis muscle. Then, signals were decomposed to extract motor unit recruitment threshold, firing rates and action potential amplitudes (MUAP). Force decrement was only seen after LI BFR exercise (-20.5%; p<0.05). LI BFR exercise also induced greater decrements in the linear slope coefficient of the regression lines between motor unit recruitment threshold and firing rate (BFR: -165.1±120.4 vs. non-BFR: -44.4±33.1%, p<0.05). Finally, there was a notable shift towards higher values of firing rate and MUAP amplitude post-LI BFR exercise. Taken together, our data indicate that LI BFR exercise increases the activity of motor units with higher MUAP amplitude. They also indicate that motor units with similar MUAP amplitudes become activated at higher firing rates post-LI BFR exercise.

Influence of full range of motion vs. equalized partial range of motion training on muscle architecture and mechanical properties.

PURPOSE: The purpose of this study was to determine the effect of a 15-week partial range of motion (ROM) resistance training program on the vastus lateralis (VL) architecture and mechanical properties, when the time under tension (TUT) was equalized. METHODS: Nineteen untrained male subjects were randomly assigned to a control (Control; n = 8) or training (TG; n = 11) group. In the TG, the dominant and nondominant legs were randomly selected to be trained with a full ROM (FULL) or a partial ROM (PART) in an isokinetic dynamometer. Training volume was equalized based on the TUT by manipulating sets and repetitions. The VL muscle architecture was assessed by B-mode ultrasonography at rest and during maximal isometric knee extension contractions (MVCs) at ten knee angles. The VL fascicle force and specific tension were calculated from the MVCs with superimposed stimuli, accounting for the moment arm length, muscle architecture, and antagonist coactivation. RESULTS: The FULL training induced changes in fascicle length (FL) (4.9 ± 2.0%, P < 0.001) and specific tension (25.8 ± 18.7%, P < 0.001). There was a moderate effect of PART training on the physiological cross-sectional area (PCSA) (7.8 ± 4.0%, P < 0.001, dav = 0.6) and torque-angle adaptations (average increase 17.7 ± 3.9%, P < 0.05). CONCLUSIONS: These results provide evidence that crucial architectural and mechanical muscle adaptations are dependent on the ROM used in strength training. It seems that muscle FL and specific tension can be increased by pure concentric training if greater ROM is used. Conversely, restricting the ROM to shorter muscle lengths promotes a greater PCSA and angle-specific strength adaptations.

Muscle fatigue in response to low-load blood flow-restricted elbow-flexion exercise: are there any sex differences?

PURPOSE: This study aimed to determine whether men and women display a different magnitude of muscle fatigue in response to high-load (HL) and low-load blood flow-restricted (LLBFR) elbow-flexion exercise. We also explored to which extent both exercise protocols induce similar levels of muscle fatigue (i.e., torque decrement). METHODS: Sixty-two young participants (31 men and 31 women) performed dynamic elbow flexions at 20 and 75% of one-repetition maximum for LLBFR and HL exercise, respectively. Maximum voluntary isometric contractions were performed before and after exercise to quantify muscle fatigue. RESULTS: Men and women exhibited similar magnitude of relative torque decrement after both exercise protocols (p > 0.05). HL was more fatiguing (∆ torque output: 11.9 and 23 N.m in women and men, respectively) than LLBFR resistance exercise (∆ torque output: 8.3 and 15.4 N.m in women and men, respectively) in both sexes, but this was largely attenuated after controlling for the differences in volume load between protocols (p > 0.05). CONCLUSIONS: These data show that torque decrement in response to LLBFR and HL dynamic elbow-flexion exercise does not follow a sexually dimorphic pattern. Our data also indicate that, if performed in a multiple-set fashion and prescribed for a given volume load, elbow-flexion LLBFR exercise induces similar levels of fatigue as HL acute training. Importantly, this occurs similarly in both sexes.

Ultrasonographic Measurement of the Biceps Femoris Long-Head Muscle Architecture.

OBJECTIVES: Biceps femoris long-head architectural assessment using ultrasonography (US) has not been previously described in detail for both acquisition (image capture) and digitization (image measurement) processes, and the effect of the US window width is unknown. This study aimed to describe the reliability and test-retest minimum detectable difference of US-based biceps femoris architectural measurements. METHODS: Muscle length was determined by marking the muscle-tendon junction distances. Sonograms were acquired with a 6-cm image width and cropped for a 3-cm width in 3 assessments (n = 20 adults). Intra- and inter-rater reliability rates were determined for both image (3- and 6-cm widths) acquisition and digitizing processes separated and together (within session) for the biceps femoris fascicle length, fascicle angle, and muscle thickness measurements using intraclass correlation coefficients (ICCs) and Pearson (r) correlation coefficients. RESULTS: Muscle length was measured with high intra-rater (ICC = 0.93; r = 0.92) and inter-rater (ICC = 0.90; r = 0.90) reliability. Intra-rater (coefficient of variation, 0.2%-1.8%) and inter-rater (ICC = 0.79-0.99; r = 0.80-0.99) digitizing reliability rates were high. High intra-rater (ICC = 0.79-0.95; r = 0.79-0.95) and moderate-to-high inter-rater (ICC = 0.51-0.92; r = 0.70-0.93) session reliability rates were found for all architectural parameters for 6- and 3-cm images (intra-rater ICC = 0.77-0.93; r = 0.79-0.93; inter-rater ICC = 0.63-0.98; r = 0.90-0.98). The inter-rater session reliability rates for both image acquisition and digitizing processes were higher for 6-cm images (ICC = 0.65-0.86; r = 0.67-0.87) than 3-cm images (ICC = 0.28-0.93; r = 0.67-0.93). The minimum detectable differences for the 6-cm images were 8.4 mm, 1.5 °, and 1.6 mm for fascicle length, fascicle angle, and muscle thickness, respectively. CONCLUSIONS: Ultrasonography can be used to reliably assess midmuscle architecture of the biceps femoris muscle when the same rater performs image acquisition and digitization.

Sexual Dimorphism in the Estimation of Upper-Limb Blood Flow Restriction in the Seated Position.

Borges, A, Teodósio, C, Matos, P, Mil-Homens, P, Pezarat-Correia, P, Fahs, C, and Mendonca, GV. Sexual dimorphism in the estimation of upper-limb blood flow restriction in the seated position. J Strength Cond Res 32(7): 2096-2102, 2018-Arterial occlusion pressure (AOP) is typically used to normalize blood flow restriction (BFR) during low-intensity BFR exercise. Despite strong evidence for sexual dimorphism in muscle blood flow, sex-related differences in AOP estimation remain a controversial topic. We aimed at determining whether the relationship of upper-limb AOP with arm circumference and systolic blood pressure (BP) differs between men and women resting in the seated position. Sixty-two healthy young participants (31 men: 21.7 ± 2.3; 31 women: 22.0 ± 2.0 years) were included in this study. Arm circumference, resting BP, and AOP were taken in the seated position. Multiple linear regression analysis was used to determine whether the relationship of AOP with arm circumference and resting BP differed between sexes. Prediction accuracy was assessed with the mean absolute percent error and Bland-Altman plots. Men had higher systolic BP and larger arm circumference than women (p < 0.05). Nevertheless, AOP was similar between sexes. Arm circumference, systolic BP, and sex were all significant predictors of AOP (p < 0.05), explaining 42% of its variance. The absolute percent error was similar in both sexes (men: -0.55 ± 7.12; women: -0.39 ± 6.31%, p > 0.05). Bland-Altman plots showed that the mean difference between actual and estimated AOP was nearly zero in both groups, with no systematic overestimation or underestimation. In conclusion, arm circumference, systolic BP, and sex are all significant predictors of upper-limb-seated AOP. Their measurement allows for the indirect estimation of BFR pressure within the context of exercise training.

Acute Neuromuscular Adaptations in Response to Low-Intensity Blood-Flow Restricted Exercise and High-Intensity Resistance Exercise: Are There Any Differences?

Fatela, P, Reis, JF, Mendonca, GV, Freitas, T, Valamatos, MJ, Avela, J, and Mil-Homens, P. Acute neuromuscular adaptations in response to low-intensity blood flow restricted exercise and high-intensity resistance exercise: are there any differences? J Strength Cond Res 32(4): 902-910, 2018-Numerous studies have reported similar neuromuscular adaptations between low-intensity (LI) blood-flow restricted exercise (BFRE) and high-intensity (HI) resistance training. Unfortunately, none of these experimental designs individualized blood flow restriction (BFR) levels to each participant. Thus, their findings are difficult to interpret. We aimed at comparing the acute effects of LI BFR (80% of absolute vascular occlusion pressure) with LI non-BFR and HI training on muscle torque, activation, and neuromuscular fatigue. Ten men (23.8 ± 5.4 years) exercised at 20 and 75% of 1 repetition maximum with and without BFR (for LI). Blood flow restriction pressure was determined individually using resting blood-flow measurements. Torque was determined during maximal voluntary contractions (MVCs) at pre-exercise and postexercise time points. Surface electromyographic activity (root mean square [RMS] and median frequency [MF]) was recorded for the rectus femoris (RF) and vastus medialis (VM) muscles, before and after each session of training, during isometric contractions at 20% MVC. Torque decreased post-HI and LI BFR (-9.5 and -7.8%, respectively; p < 0.01), but not after LI non-BFR. The MF was reduced following HI training in the VM and the RF muscles (-5.3 and -12.5%, respectively; p ≤ 0.05). Conversely, the impact of LI BFR on reducing MF was limited to the RF muscle (-10.7%, p ≤ 0.05). Finally, when compared to all other conditions, RMS values were consistently higher during submaximal contractions performed after HI training (p ≤ 0.05). Thus, we conclude that, despite enhancing the acute magnitude of muscular activation and fatigue, LI BFR exercise exerts a less profound impact on neuromuscular function than HI resistance training.

Acute muscle and joint mechanical responses following a high-intensity stretching protocol.

PURPOSE: A previous study observed a joint passive torque increase above baseline ~30 min after a high-intensity stretching. This study examined the effect of a high-intensity stretching on ankle dorsiflexion passive torque, medial gastrocnemius (MG) shear modulus, and plantar flexors maximal voluntary isometric force (MVIC). METHOD: Participants (n = 11, age 27.2 ± 6.5 years, height 172.0 ± 10.0 cm, weight 69.5 ± 10.4 kg) underwent two stretching sessions with plantar flexors isometric contractions performed: (1) 5 min before, 1 min after, and every 10 min after stretching (MVC session); (2) 5 min before, and 60 min after the stretching (no-MVC session). RESULTS: In both sessions, no changes were observed for MG shear modulus (p > 0.109). In the no-MVC session, passive torque decreased 1 min after stretching (-7.5 ± 8.4 %, p = 0.015), but increased above baseline 30 min after stretching (+6.3 ± 9.3 %, p = 0.049). In the MVC session, passive torque decreased at 1 min (-10.1 ± 6.3 %, p < 0.001), 10 min (-6.3 ± 8.2 %, p = 0.03), 20 min (-8.0 ± 9.2 %, p = 0.017), and 60 min (-9.2 ± 12.4 %, p = 0.034) after the stretching, whereas the MVIC decreased at 1 min (-5.0 ± 9.3 %, p = 0.04) and 10 min (-6.7 ± 8.7 %, p = 0.02) after stretching. CONCLUSION: The ankle passive torque increase 30 min following the stretch was not due to the MG shear modulus response; consequently, response may be due to changes in surrounding connective tissue mechanical properties.

Acute effects of exercise under different levels of blood-flow restriction on muscle activation and fatigue.

PURPOSE: There is some evidence that muscular activation during exercise is enhanced by higher levels of blood flow restriction (BFR). However, the impact of different relative levels of BFR on the acute neuromuscular response to resistance exercise is not yet fully understood. We examined the acute effects of low-intensity knee extensions [20 % of 1-repetition maximum (1RM)] with BFR on muscle activation, neuromuscular fatigue and torque in the rectus femoris (RF) and vastus medialis (VM) muscles. METHODS: Fourteen men (24.8 ± 5.4 years) exercised at 20 % 1RM combined with 40, 60 and 80 % BFR. Restrictive pressures were calculated based on direct blood-flow measurements taken at rest on each participant. Torque was determined during pre- and post-exercise maximal voluntary contractions. Surface electromyographic activity [root mean square (RMS)] was obtained during dynamic and sustained isometric contractions before and after exercise. The median frequency (MF) of the electromyographic power spectrum was computed for isometric contractions. RESULTS: Torque only decreased in the 80 % BFR condition (-5.2 %; p < 0.01). Except for the VM in the 40 % BFR, MF decreased in both muscles post-exercise in all conditions (p < 0.01). MF decrements were of greater magnitude post-exercise at higher levels of BFR. RMS increased within all sets in both muscles (p < 0.01) and attained higher values in the 80 % BFR condition; except for set 1 in the RF muscle (p < 0.01). CONCLUSION: Muscular activation, as well as neuromuscular fatigue, varies as a function of relative BFR intensity. Therefore, the individual determination of vascular restriction levels is crucial before engaging in BFR exercise.

Muscle and joint responses during and after static stretching performed at different intensities.

PURPOSE: We investigated the effects of plantarflexor static stretching of different intensities on the medial gastrocnemius (GAS) shear elastic modulus, GAS fascicle length and ankle passive torque-angle responses during and after stretching. METHODS: Participants performed three stretching sessions of different intensities: 40 % (R40) of maximal dorsiflexion range of motion (ROM), 60 % (R60) of ROM, and 80 % (R80) of ROM. Each stretching lasted 10 min. The GAS architecture, GAS shear elastic modulus, ankle passive torque-angle, and muscle activity were assessed before, during, and after the stretching. RESULTS: The absolute and relative (i.e., normalized to the static stretching start value) GAS shear elastic modulus relaxation varied across stretching intensities. The absolute passive torque relaxation varied across intensities (p < 0.05) but not when normalized to the stretching start value. No significant changes were observed in GAS fascicle length during the stretching (p = 0.93). After stretching, passive torque at a given angle was significantly decreased for R60 [-0.99 ± 0.59 Nm (-6.5 ± 3.8 %), p < 0.001] and R80 [-1.05 ± 1.12 Nm (-6.8 ± 6.3 %), p = 0.004], and GAS shear elastic modulus decreased only for the R80 [-9.3 ± 7.2 kPa (-14.1 %), p = 0.003]. No significant correlations were found between the magnitude of relaxation during stretching and post-stretching effect in the GAS shear elastic modulus or ankle passive torque variables. No significant relation was found between the shear elastic modulus and the ankle passive torque responses during and after stretching. CONCLUSION: The effects of stretching on joint passive torque do not reflect changes in the medial gastrocnemius shear elastic modulus, and these responses to stretching depend on its intensity.

Effect of 8-week high-intensity stretching training on biceps femoris architecture.

Previous studies have reported no changes on muscle architecture (MA) after static stretching interventions; however, authors have argued that stretching duration and intensity may not have been sufficient. A high-intensity stretching intervention targeting the knee flexors with an 8-week duration was conducted to observe the effects on biceps femoris long head (BF) architecture. Participants (n = 5) performed an average of 3.1 assisted-stretching sessions per week, whereas a control group (n = 5) did not perform stretching. The knee extension passive maximal range of motion (ROM), and BF fascicle length (FL), fascicle angle, and muscle thickness were assessed before and after the intervention. A significant increase was observed for FL (+12.3 mm, p = 0.04) and maximal ROM (+14.2°, p = 0.04) for the stretching group after the intervention. No significant changes were observed for the control group in any parameter. An 8-week high-intensity stretching program was observed to efficiently increase the BF FL, as well as the knee extension maximal ROM. Stretching intensity and duration may play an important role on MA adaptation.

A New Tool to Assess the Perception of Stretching Intensity.

This study aimed to develop a valid and reliable scale to assess the perception of stretching intensity below and above the maximal range of motion. Experiments were conducted through a passive leg extension angle-torque assessment to healthy population (n = 90). In the study's first phase, the visual, numerical, and description of the stretching intensity scale (SIS) components were developed. The visual analog scale (VAS) score, absolute magnitude estimation (AME) score, and verbal stretching intensity symptom descriptors were assessed for different stretching intensities. In the second phase, the SIS was tested for validity, reliability, scale production, and estimation properties as well as responsiveness to stretching. In the first phase, a high correlation was found between SIS score and range of motion (ROM), as well as SIS and torque in both submaximal (intraclass correlation coefficient [ICC] = 0.89-0.99, r = 0.88-0.99) and supramaximal (ICC = 0.75-0.86, r = 0.68-0.88) stretching intensities. The AME and VAS scores fitted well in an exponential model for submaximal stretching intensities (y = 14.829e, ICC = 0.97 [0.83-0.99], r = 0.98), and in a linear model for supramaximal stretching intensities (y = 0.7667x - 25.751, ICC = 0.97 [0.89-0.99], r = 0.9594). For the second phase, a high correlation was found between SIS score and ROM (r = 0.70-0.76, ICC = 0.76-0.85), as well as SIS and torque (r = 0.62-0.88, ICC = 0.57-0.85). The interday reliability was high to produce (r = 0.70, ICC = 0.70 [0.50-0.83]) or estimate (r = 0.89, ICC = 0.89 [0.82-0.93]) stretching intensities. The acute stretching effects on ROM and passive torque were detectable using the SIS. It is expected a high application in assessing the stretch intensity using the SIS in future studies and practical interventions.

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.

Monitoring Training Volume Through Maximal Number of Repetitions or Velocity-Based Approach.

PURPOSE: This study aimed (1) to analyze the interindividual variability in the maximal number of repetitions (MNR) performed against a given relative load (percentage of 1-repetition maximum [%1RM]) and (2) to examine the relationship between the velocity loss (VL) magnitude and the percentage of completed repetitions with regard to the MNR (%Rep), when the %1RM is based on individual load-velocity relationships. METHODS: Following an assessment of 1RM strength and individual load-velocity relationships, 14 resistance-trained men completed 5 MNR tests against loads of 50%, 60%, 70%, 80%, and 90% 1RM in the Smith machine bench-press exercise. The relative loads were determined from the individual load-velocity relationship. RESULTS: Individual relationships between load and velocity displayed coefficients of determination (R2) ranging from .986 to .998. The MNR showed an interindividual coefficient of variation ranging from 8.6% to 33.1%, increasing as the %1RM increased. The relationship between %Rep and the magnitude of VL showed a general R2 of .92 to .94 between 50% and 80% 1RM, which decreased to .80 for 90% 1RM. The mean individual R2 values were between .97 and .99 for all loading conditions. The %Rep when a given percentage of VL was reached showed interindividual coefficient of variation values ranging from 5% to 20%, decreasing as the %Rep increased in each load condition. CONCLUSIONS: Setting a number of repetitions had acceptable interindividual variability, with moderate relative loads being adjusted based on the individual load-velocity relationship. However, to provide a more homogeneous level of effort between athletes, the VL approach should be considered, mainly when using individual VL-%Rep relationships.

Rapid hamstrings to quadriceps ratio at long muscle lengths in professional football players with previous hamstring strain injury.

Hamstring strain injuries (HSI) are the most common injury in male professional football and are potentially a primary risk factor to re-injury. Although the isokinetic strength ratios have often been used to identify strength imbalances that can augment the risk of injury in football players, the rate of torque development hamstring to quadriceps ratio (RTD H/Q) has rarely been considered in previous reports. Furthermore, little consideration has been given to selective hamstring lengths (30° of knee flexion) and its influence on torque production. The aim of this study was to investigate the RTD H/Q at long hamstring lengths, conventional (concentric/concentric) and functional (eccentric/concentric) H/Q ratios in football players with and without previous HSI. Twenty-four professional male football players (12 and 12 without previous HSI) performed maximal voluntary isometric contractions at long hamstring lengths (knee and hip flexed at 30° and 85°, respectively) and isokinetic concentric and eccentric contractions at 180°.s-1 and 60°.s-1. Conventional and functional H/Q ratios based on peak torque throughout the entire isokinetic range of motion and at long hamstring lengths were calculated. The RTD H/Q was extracted at long hamstring lengths in incrementing time periods of 50 milliseconds (ms) from the onset of contraction (50-250 ms). No significant differences were found between groups in any H/Q ratios studied. However, small effects (d = 0.4) were found in previously injured hamstrings to lower RTD H/Q at 50 ms and flexor eccentric torque. Previous HSI group showed small to moderate (0.4 > d < 0.6) higher RTD H/Q in late time intervals (>100 ms).

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

Ultrasound imaging allows the evaluation of musculoskeletal morphology and function. Ultrasound elastography can also offer semi-quantitative and/or quantitative assessment of tissue stiffness providing relevant information about adaptations of skeletal muscle mechanical properties. In this study we aimed to explore the feasibility of elastography ultrasound imaging in assessing the effect of strength training on vastus lateralis stiffness. Twenty-eight young male adults were separated in a control (n = 9) and strength-training (n = 20) groups. The strength-training group completed 15 weeks of either concentric (n = 10) or eccentric (n = 10) isokinetic training of the knee extensors. Ultrasound scans of the vastus lateralis for quasi-static elastography were collected. All image acquisitions and measurements were done by the same experienced sonographer. After 15 weeks, knee maximal extension isometric torque increased in the strength-training groups. After strength training, there was a decrease in the amount of red pixels in vastus lateralis region of interest [F(1,18) = 25.490; p < 0.001; η2 = 0.586], whereas the amount of green and blue pixels increased F(1,18) = 17.179; p < 0.01; η2 = 0.488; F(1,18) = 6.522; p < 0.05; η2 = 0.266], suggesting higher vastus lateralis stiffness. We conclude that concentric and eccentric strength training increases skeletal muscle stiffness, which can be evaluated by quasi-static elastography. Ultrasound elastography is suitable for non-invasive evaluation of skeletal muscle functional adaptations, which can be of importance for sports medicine and in designing optimal training and rehabilitation programs.

Improving the Reliability of V-Wave Responses in the Soleus Muscle.

PURPOSE: The V wave is an electrophysiologic variant of the H reflex that is evoked with supramaximal stimulus intensity. In this study, we explored whether the between-day reliability of V-wave normalized amplitude varies as a function of the number of intrasession measurement trials. We also determined whether the reliability of the V wave improves after the exclusion of the initial testing trials. METHODS: Eighteen healthy, young participants (10 men and 8 women) were included in this study. Test-retest reliability was assessed using intraclass correlation coefficients and the standard error of the measurement (1.96*SEM). RESULTS: The intraclass correlation coefficient values of the V-wave normalized amplitude increased in a progressive fashion with the inclusion of more than two measurement trials (from 0.41 to 0.75). The 1.96*SEM scores also decreased from 12.47% to 7.60% after calculating the V-wave normalized amplitude from five versus two measurement trials. After excluding the first two trials from V-wave calculations, the intraclass correlation coefficient and the 1.96*SEM score attained values of 0.88 and 6.54%, respectively. CONCLUSIONS: Our findings indicate that the test-retest reliability of the V-wave response increases in a progressive fashion with more than two intrasession measurement trials (up to five trials). It also shows that to ensure maximal reliability, the first two measurement trials should be discarded from V-wave computations.