Force Production Measurements During a Supine Medicine Ball Throw: a Reliability and Correlation Study.

OBJECTIVES: This study aimed to examine the reliability of supine medicine ball throw peak force and rate of force development (RFD) measurements. A secondary aim was to investigate the correlations between these measurements and vertical jump height. METHODS: Twenty young women (21±3 years) reported for experimental testing on two different occasions. Supine medicine ball throw assessments were performed during each testing session to assess peak force, RFDmax, and RFD at specific percentages of peak force (RFD30% and RFD40-80%). Vertical jumps were performed on a jump mat. The jump mat measured vertical jump height based on flight time. RESULTS: Good intraclass correlation coefficients (≥0.82) and coefficients of variation (≤14.0%) were observed between sessions for peak force, RFDmax, and RFD40-80%, but not for RFD30% (0.55, 27.2%). There were significant correlations between jump height and peak force (r=0.483, P=0.031), RFDmax (r=0.484, P=0.031), and RFD40-80% (r=0.491, P=0.028). There was no significant correlation between jump height and RFD30% (r=0.359, P=0.120). CONCLUSIONS: Our results showed that supine medicine ball throw peak force, RFDmax, and RFD40-80% were reliable measures for assessing upper-body explosive strength in young adults. These measurements were significantly associated with vertical jump height and therefore, may be effective predictors of one's athletic ability.

Strategies for Improving Firefighter Health On-Shift: A Review.

The fire service suffers from high rates of cardiovascular disease and poor overall health, and firefighters often suffer fatal and non-fatal injuries while on the job. Most fatal injuries result from sudden cardiac death, while non-fatal injuries are to the musculoskeletal system. Previous works suggest a mechanistic link between several health and performance variables and injury risk. In addition, studies have suggested physical activity and nutrition can improve overall health and occupational performance. This review offers practical applications for exercise via feasible training modalities as well as nutritional recommendations that can positively impact performance on the job. Time-efficient training modalities like high-intensity interval training and feasible modalities such as resistance training offer numerous benefits for firefighters. Also, modifying and supplementing the diet and can be advantageous for health and body composition in the fire service. Firefighters have various schedules, making it difficult for planned exercise and eating while on shift. The practical training and nutritional aspects discussed in this review can be implemented on-shift to improve the overall health and performance in firefighters.

Influence of body mass normalization on the correlations between muscle cross-sectional area and physical performance outcomes in older women.

AIMS: Normalization is a method used to account for body mass in clinical practice and research. It is unclear if this method will improve the correlation between muscle cross-sectional area (CSA) and physical performance. We examined the correlations between quadriceps muscle morphology parameters and physical performance outcomes in older women. Material and methods: Twenty older women participated in this study. Ultrasound imaging was used to measure quadriceps muscle CSA and echo intensity. Muscle CSA was expressed as an absolute value (cm2) and as a relative value normalized to body mass (cm2/kg). Physical performance was assessed from timed up-and-go and 6-min walk tests. RESULTS: Relative CSA was significantly related to timed up-and-go scores (r=-0.489, p=0.029) and 6-min walking speed (r=0.606, p=0.005), whereas absolute CSA was not significantly associated with these performances (r=-0.231, p=0.327 and r=0.373, p=0.105). There was a significant correlation between absolute CSA and body mass (r=0.456, p=0.043). There were also significant correlations between echo intensity and timed up-and-go scores (r=0.556, p=0.011) and 6-min walking speed (r=-0.484, p=0.031). CONCLUSIONS:  Our study showed that relative CSA correlated better than absolute CSA with physical performance. These findings support the need to normalize measurements of muscle CSA to body mass in older adults.

Skeletal muscle estimation: A review of techniques and their applications.

Quantifying skeletal muscle size is necessary to identify those at risk for conditions that increase frailty, morbidity, and mortality, as well as decrease quality of life. Although muscle strength, muscle quality, and physical performance have been suggested as important assessments in the screening, prevention, and management of sarcopenic and cachexic individuals, skeletal muscle size is still a critical objective marker. Several techniques exist for estimating skeletal muscle size; however, each technique presents with unique characteristics regarding simplicity/complexity, cost, radiation dose, accessibility, and portability that are important factors for assessors to consider before applying these modalities in practice. This narrative review presents a discussion centred on the theory and applications of current non-invasive techniques for estimating skeletal muscle size in diverse populations. Common instruments for skeletal muscle assessment include imaging techniques such as computed tomography, magnetic resonance imaging, peripheral quantitative computed tomography, dual-energy X-ray absorptiometry, and Brightness-mode ultrasound, and non-imaging techniques like bioelectrical impedance analysis and anthropometry. Skeletal muscle size can be acquired from these methods using whole-body and/or regional assessments, as well as prediction equations. Notable concerns when conducting assessments include the absence of standardised image acquisition/processing protocols and the variation in cut-off thresholds used to define low skeletal muscle size by clinicians and researchers, which could affect the accuracy and prevalence of diagnoses. Given the importance of evaluating skeletal muscle size, it is imperative practitioners are informed of each technique and their respective strengths and weaknesses.

Short-term Effects of Static Stretching on Hamstring Passive Stiffness in Young and Older Women.

OBJECTIVES: The objectives of this study were to assess the acute effects of static stretching on hamstring passive stiffness in young and older women. A secondary objective was to compare hamstring muscle size and quality measurements (cross-sectional area and echo intensity) between the two groups and to determine if these characteristics are related to passive stiffness at baseline. METHODS: Fifteen young (23±4 years) and 15 older (73±5 years) women underwent two randomized conditions that included a control treatment and an experimental treatment of four, 15-s static stretches of the hamstrings. Passive stiffness was calculated before (pre-test) and after (post-test) each treatment using a passive knee extension test. Ultrasound imaging was used to measure hamstring muscle cross-sectional area and echo intensity. RESULTS: Passive stiffness collapsed across group decreased from pre- to post-test for the stretching treatment (P=0.001) but not for the control (P=0.467). The older women had lower cross-sectional area (P=0.033) and greater baseline (pre-test) passive stiffness (P=0.042-0.049) and echo intensity (P=0.022) than the young women. Moreover, baseline passive stiffness was significantly related to echo intensity (r=0.430, P=0.018) but not cross-sectional area (r=-0.014, P=0.943). CONCLUSION: An acute bout of static stretching decreased passive stiffness in both young and older women.

Tradeoffs of estimating reaction time with absolute and relative thresholds.

Measuring the duration of cognitive processing with reaction time is fundamental to several subfields of psychology. Many methods exist for estimating movement initiation when measuring reaction time, but there is an incomplete understanding of their relative performance. The purpose of the present study was to identify and compare the tradeoffs of 19 estimates of movement initiation across two experiments. We focused our investigation on estimating movement initiation on each trial with filtered kinematic and kinetic data. Nine of the estimates involved absolute thresholds (e.g., acceleration 1000 back to 200 mm/s2, micro push-button switch), and the remaining ten estimates used relative thresholds (e.g., force extrapolation, 5% of maximum velocity). The criteria were the duration of reaction time, immunity to the movement amplitude, responsiveness to visual feedback during movement execution, reliability, and the number of manually corrected trials (efficacy). The three best overall estimates, in descending order, were yank extrapolation, force extrapolation, and acceleration 1000 to 200 mm/s2. The sensitive micro push-button switch, which was the simplest estimate, had a decent overall score, but it was a late estimate of movement initiation. The relative thresholds based on kinematics had the six worst overall scores. An issue with the relative kinematic thresholds was that they were biased by the movement amplitude. In summary, we recommend measuring reaction time on each trial with one of the three best overall estimates of movement initiation. Future research should continue to refine existing estimates while also exploring new ones.

Can handgrip strength measurements predict postural balance performance in older women?

OBJECTIVES: The link between handgrip strength and postural balance in older adults is not well understood. This study aimed to examine the correlations between postural balance performance and handgrip peak force and rate of force development (RFD) measurements in older women. METHODS: Twenty older women (67 ± 5 years) participated in this study. Handgrip contractions were used to assess peak force, peak RFD, and RFD at 0-100 (RFD100) and 0-200 (RFD200) ms. Postural balance was evaluated using a commercially designed balance testing device, which provides a measurement of static stability based on the sway index. RESULTS: There were significant correlations between sway index and handgrip peak force (r = -0.497, P = 0.026), peak RFD (r = -0.552, P = 0.012), RFD100 (r = -0.539, P = 0.014), and RFD200 (r = -0.499, P = 0.025). Stepwise multiple regression analysis indicated that handgrip peak RFD was the single best predictor of sway index (R2 = 0.305). The other variables, including peak force, did not add any unique variance to the stepwise prediction model. CONCLUSION: These findings suggest that handgrip strength, and in particular peak RFD, may be an effective parameter at predicting postural balance performance in older women.

Reliability of handgrip strength measurements and their relationship with muscle power.

BACKGROUND: Handgrip peak force and rate of force development (RFD) have been shown to be useful measurements at characterizing the strength capacities of numerous muscle groups, including those of the lower extremities. However, the reliability of these measurements and their relationship with peak muscle power remain uncertain. We aimed to examine the reliability of handgrip peak force and RFD measurements. A secondary aim was to determine if these measurements are correlated with peak muscle power. METHODS: Twenty young women (21±3 years) reported for testing on two different occasions. Handgrip contractions were performed during each testing session to assess peak force, peak RFD, and RFD at 0-100 (RFD100) and 0-200 (RFD200) ms. Peak power was assessed from a vertical jump test. RESULTS: Handgrip peak force and RFD measurements were highly consistent between sessions, with intraclass correlation coefficients of 0.89-0.92 and coefficients of variation of 4.9-6.4%. There were significant correlations between peak power and handgrip peak force (r=0.612, P=0.004), peak RFD (r=0.731, P<0.001), RFD100 (r=0.671, P=0.001), and RFD200 (r=0.701, P=0.001). Stepwise multiple regression analysis indicated that handgrip peak RFD was the single best predictor of peak power (R2=0.535). CONCLUSIONS: Our results showed that handgrip peak force and RFD measurements are highly reliable and significantly associated with performance during a vertical jump test. The output from our multiple regression analysis suggests that handgrip peak RFD may be an effective predictor of muscle power.

Rate of torque development as a discriminator of playing level in collegiate female soccer players.

OBJECTIVES: This study aimed to examine the efficacy of isometric knee extension and flexion peak torque and rate of torque development (RTD) variables to distinguish starters from non-starters in collegiate female soccer players. METHODS: Eleven starters (20±2 years) and 13 non-starters (19±1 years) performed three isometric maximal voluntary contractions of the knee extensors and flexors. Peak torque, peak RTD, and RTD at 0-100 (RTD100) and 0-200 (RTD200) ms were obtained from each contraction. RESULTS: The starters produced significantly greater (P=0.002-0.015) knee extension and flexion peak RTD, RTD100, and RTD200 values than the non-starters. There were no significant differences (P>0.050) between the starters and non-starters for peak torque. Discriminant analysis revealed thresholds of 9.36, 7.98, and 6.97 Nm⋅s-1⋅kg-1 for knee extension RTD200 and knee flexion peak RTD and RTD100, respectively. These thresholds showed 81.8% sensitivity and 76.9 to 92.3% specificity for identifying playing group membership. CONCLUSIONS: Our findings indicate that RTD may be a better parameter than peak torque at differentiating between playing level in collegiate female soccer players. The discriminant analysis thresholds for the RTD variables demonstrated good sensitivity and specificity, and therefore, may be used as indices to identify players with a high degree of soccer playing ability.

Correcting for subcutaneous fat: Does it improve the correlation between vastus lateralis echo intensity and physical performance in older women?

Numerous studies have corrected the echo intensity of the vastus lateralis for subcutaneous fat thickness. However, it is unclear if correction for subcutaneous fat improves the correlation between vastus lateralis echo intensity and physical performance. We aimed to examine the correlations between vastus lateralis muscle morphology parameters and physical performance outcomes in older women. Twenty healthy older women (67 ± 4 years) participated in this study. Muscle cross-sectional area, raw and corrected echo intensity and subcutaneous fat thickness were determined from ultrasound scans of the vastus lateralis. Physical performance was assessed from timed up-and-go and 6 min walk tests. Raw echo intensity was significantly related to timed up-and-go scores (r = 0.552, p = 0.012) and 6 min walk distance (r = -0.462, p = 0.040), whereas corrected echo intensity was not significantly associated with these performances (r = 0.433, p = 0.056 and r = -0.373, p = 0.105). There was a nonsignificant correlation between raw echo intensity and subcutaneous fat thickness (r = 0.353, p = 0.126). There were also nonsignificant correlations between muscle cross-sectional area and timed up-and-go scores (r = -0.189, p = 0.426) and 6 min walk distance (r = 0.298, p = 0.201). The results of our study showed that raw echo intensity correlated better than corrected echo intensity with physical performance. These findings question the need to correct the echo intensity of the vastus lateralis for subcutaneous fat thickness in older adults.

Changes in Knee Extension and Flexion Maximal and Rapid Torque Characteristics During a Collegiate Women's Soccer Season.

ABSTRACT: Akehi, K, Palmer, TB, Conchola, EC, Thompson, BJ, Kasl, A, Bice, M, and Unruh, S. Changes in knee extension and flexion maximal and rapid torque characteristics during a collegiate women's soccer season. J Strength Cond Res 36(5): 1389-1395, 2022-The purpose of this study was to assess the changes in maximal and rapid torque capacities of the knee extensor and flexor muscles over the course of a competitive season in NCAA Division II women's soccer players. Eighteen female soccer athletes performed 2 maximal voluntary isometric contractions (MVICs) of the knee extensor and flexor muscles before, during, and at the end of the competitive season. Peak torque (PT) and rate of torque development (RTD) at 50 (RTD50), 200 (RTD200), and 100-200 (RTD100-200) milliseconds were extracted from each MVIC for both legs. The rapid (RTD50) to maximal force ratio (RTD:PT), hamstring-to-quadriceps (H:Q) strength ratio, and bilateral strength differences were also calculated. Results indicated that PT, RTD50, and RTD200 decreased 11-21% from the preseason to the midseason for the knee extensors (p < 0.02) and RTD50 increased approximately 11% from the midseason to the end of season for the knee flexors (p < 0.01). Rate of torque development-to-PT ratios for the knee extensors and flexors increased 12-25% at the end of the season (p < 0.05). Also, H:Q strength ratios using PT, RTD50, and RTD200 increased 12.5-24% after the season started (p = 0.001-0.04). There were no bilateral strength differences (dominant vs. non-dominant limbs) across the season (p > 0.05). These findings suggest that participation in a soccer season can change maximal and rapid torque production of the knee extensors and flexors. Coaches and clinicians should consider incorporating a season-long strength training and maintenance plan for soccer players with the aim to improve athletic performance and minimize the risk of musculoskeletal injuries to the lower extremities.

The time course of passive stiffness responses following an acute bout of static stretching in healthy, elderly men.

BACKGROUND: The time course of passive stiffness responses following an acute bout of static stretching has received little research attention, particularly in older adults. OBJECTIVE: To determine the time course of the acute effects of static stretching on passive stiffness of the hamstrings in healthy, elderly men. METHODS: Fifteen elderly men (age = 70 ± 7 years) underwent two randomized conditions that included a control treatment and an experimental treatment of four, 15-s straight-leg raise static stretches. Passive stiffness was calculated as the slopes of the initial and final phases of the angle-torque curve at pre-treatment (Pre) and post-treatment time points of zero (Post0), five (Post5), and ten (Post10) minutes. RESULTS: Passive stiffness collapsed across phase was lower at Post0 (P= .029, d= 0.64) and Post5 (P= .042, d= 0.54) but not Post10 (P> .999, d= 0.15) compared to Pre for the stretching treatment. There were no significant differences in passive stiffness (collapsed across phase) between any of the time points (P> .999, d≤ 0.14) for the control. CONCLUSIONS: An acute bout of static stretching produced significant decreases in the passive stiffness characteristics of elderly men; however, these decreases returned to baseline values within 5 to 10 minutes.

The Acute Effects of Fast-Paced Walking on Isometric Peak Torque and Rate of Torque Development in Regularly Exercising and Inactive Older Women.

This study aimed to examine the acute effects of fast-paced walking on isometric peak torque and rate of torque development (RTD) in regular exercising and inactive older women. Ten regular exercising (67 ± 4 years) and 10 inactive (68 ± 4 years) older women performed three isometric knee extension contractions before and after a control condition (quiet resting) and an experimental condition of fast-paced walking for 6 min. Peak torque and early (RTD100), late (RTD200), and maximum (peak RTD) RTD measurements were obtained from each contraction. Results showed no significant changes in peak torque, peak RTD, or RTD200 after walking for either group (p > .050). A significant decrease in RTD100 was observed after walking for the inactive group (p = .005) but not for the regular exercisers (p = .909). These findings highlight the importance of physical activity and suggest that a task as simple as walking may impair the rapid strength capacities of inactive older women.

Utility of peak torque and rate of torque development characteristics to identify walking performance ability in older women.

OBJECTIVES: It is unclear whether peak torque and rate of torque development (RTD) measurements can characterize functional differences in older adults according to their performance on a six-minute walk test. This study aimed to examine the efficacy of isometric peak torque and RTD characteristics of the knee extensors to differentiate between functional status in older women who are able (higher functioning) versus those who are unable (lower functioning) to walk 550 m in six minutes. METHODS: Ten higher functioning (67±4 years) and 10 lower functioning (68±4 years) older women performed three isometric knee extension maximal voluntary contractions followed by a six-minute walk test. Peak torque and early (RTD100), late (RTD200), and maximum (Peak RTD) RTD measurements were obtained from each contraction. RESULTS: The higher functioning group exhibited greater peak torque, Peak RTD, RTD100, and RTD200 compared to the lower functioning group (P≤0.011), with larger differences occurring for RTD characteristics (39.9-54.9%) than peak torque (20.3%). Multiple regression analysis indicated that RTD200 was the single best predictor of the distance covered during the six-minute walk test (R2=0.437, P=0.002). CONCLUSIONS: These findings suggest that knee extensor muscle strength, and in particular RTD, may be an effective discriminator and predictor of walking performance ability in older women.

Rapid muscle activation changes across a competitive collegiate female soccer season.

OBJECTIVE: The purpose of this study was to examine the effects of a competitive soccer season on rapid activation properties of the knee extensors and flexors in Division II female soccer players. METHODS: Eighteen collegiate female soccer players participated in the present study, however, due to injuries during the season a final sample of 16 players were included for study analysis. Participants performed two maximal voluntary isometric contractions (MVICs) of the knee extensors and flexors before, during, and at the end of a competitive college soccer season. Electromyography root mean square (EMG RMS; µV), rate of EMG rise (RER; %Peak EMG•s-1), and electromechanical delay (EMD; ms) were examined on both legs for the knee extensors and flexors. RESULTS: EMG RMS at early time intervals (0-50, 0-100, and 50-100 ms) and RER at 0-75 ms for the knee extensors and flexors significantly increased from the pre-season to the end of the season (P≤0.010-0.026, η2=0.36-0.81). EMD of the knee flexors significantly decreased at the mid-season and the end of the season compared to the pre-season (P<0.001, η2=0.95). CONCLUSIONS: These findings may have important implications for monitoring improvements on thigh neuromuscular activation and developing lower extremity injury prevention strategies during a competitive collegiate female soccer season.

Age-Related Differences in Hip Flexion Maximal and Rapid Strength and Rectus Femoris Muscle Size and Composition.

This study aimed to examine the effects of age on hip flexion maximal and rapid strength and rectus femoris (RF) muscle size and composition in men. Fifteen young (25 [3] y) and 15 older (73 [4] y) men performed isometric hip flexion contractions to examine peak torque and absolute and normalized rate of torque development (RTD) at time intervals of 0 to 100 and 100 to 200 milliseconds. Ultrasonography was used to examine RF muscle cross-sectional area and echo intensity. Peak torque, absolute RTD at 0 to 100 milliseconds, and absolute and normalized RTD at 100 to 200 milliseconds were significantly lower (P = .004-.045) in the old compared with the young men. The older men exhibited lower cross-sectional area (P = .015) and higher echo intensity (P = .007) than the young men. Moreover, there were positive relationships between cross-sectional area and absolute RTD at 0 to 100 milliseconds (r = .400) and absolute RTD at 100 to 200 milliseconds (r = .450) and negative relationships between echo intensity and absolute RTD at 100 to 200 milliseconds (r = -.457) and normalized RTD at 100 to 200 milliseconds (r = -.373). These findings indicate that hip flexion maximal and rapid strength and RF muscle size and composition decrease in old age. The relationships observed between ultrasound-derived RF parameters and measurements of RTD suggest that these age-related declines in muscle size and composition may be relevant to hip flexion rapid torque production.

Real-time measurement of isometric peak torque and rate of torque development using a novel strength testing device: a validity and reliability study.

Objective: Isometric peak torque (PT) and rate of torque development (RTD) are important characteristics relevant to athletic performance. A novel device called the Dynamo Torque Analyzer calculates and displays real-time measurements of isometric PT and RTD. However, the ability of the Dynamo to provide valid and reliable isometric PT and RTD measurements similar to those of an isokinetic dynamometer remains unclear. This study aimed to compare the reliability and magnitude of isometric leg extension and flexion PT and RTD measurements between an isokinetic dynamometer and the Dynamo Torque Analyzer.Approach: Twenty healthy, recreationally-active adults (age = 22 ± 3 years; height = 169 ± 10 cm; mass = 71 ± 18 kg) performed three isometric leg extension and flexion maximal voluntary contractions on two different occasions, from which isometric PT and early (RTD100), late (RTD200), and maximum (Peak RTD) RTD characteristics were measured by an isokinetic dynamometer and the Dynamo.Main results: Isometric leg extension and flexion PT and RTD characteristics were highly consistent across sessions for both the isokinetic dynamometer and Dynamo devices, with intraclass correlation coefficients of 0.935-0.984 and standard errors of measurement expressed as a percentage of the mean of 4.93-14.46%. There were significant positive relationships between the isokinetic dynamometer and Dynamo for all PT and RTD characteristics (r≥ 0.994;P< 0.001). Moreover, no significant differences between devices were observed for these variables (P= 0.107-0.555).Significance: These findings suggest that the Dynamo Torque Analyzer may be a valid and reliable device for measuring isometric PT and RTD of the lower-body musculature.

Effects of age on vertical jump performance and muscle morphology characteristics in females.

BACKGROUND: Declines in muscle morphology and function are commonly reported as a consequence of aging. However, few studies have investigated the influence of age on a comprehensive set of muscle function-related measures (i.e., reactive strength, power, etc.) that focuses on a dynamic performance task such as the vertical jump across the adult life span. This study aimed to examine the effects of age on muscle morphology characteristics (muscle cross-sectional area [CSA] and echo intensity [EI]) and vertical jump height, power, and reactive strength index (RSI) in females. METHODS: Twenty-six young (22±2 years), 30 middle-aged (36±5 years), and 23 older (71±5 years) females participated in this study. Muscle CSA and EI were determined from ultrasound scans of the vastus lateralis. Countermovement jumps were used to assess jump height, RSI, movement time, and peak power (Pmax). RESULTS: Muscle CSA, jump height, and Pmax were higher for the young compared to the old and middle-aged (P≤0.027) and for the middle-aged compared to the old (P<0.001). Movement time and EI values were lower (P≤0.004) and RSI values were higher (P<0.001) for the young and middle-aged compared to the old; however, no differences were observed between the young and middle-aged (P=0.367-0.620). CONCLUSIONS: Of all the variables assessed in this study, RSI exhibited the greatest decline (76%) between the young and old females. Such findings highlight the importance of reactive strength when assessing age-related changes in neuromuscular performance.

Relationships between hamstring morphological characteristics and postural balance in elderly men.

OBJECTIVES: The link between hamstring morphology and postural balance performance in older adults is not well understood. This study aimed to examine the relationships between hamstring morphological characteristics of muscle size (cross-sectional area [CSA]) and quality (echo intensity [EI]) and postural balance with the eyes open and closed in elderly men. METHODS: Nineteen healthy elderly men (age= 73±4 years) participated in this study. Muscle CSA and EI were determined from ultrasound scans of the hamstrings. Postural balance was assessed with the eyes open and closed using a commercially designed balance testing device, which provides a measurement of static stability based on the sway index. RESULTS: The sway index with eyes closed was significantly related to muscle EI (r=0.474; P=0.040) but not CSA (r=0.021; P=0.932). The sway index with eyes open was not related to muscle CSA (r= -0.036; P=0.883) or EI (r=-0.079; P=0.747). CONCLUSIONS: The significant relationship observed between the sway index with eyes closed and muscle EI suggests that hamstring muscle quality may be a characteristic relevant to postural balance in the absence of visual feedback. These findings may provide important insight regarding the morphological mechanisms involved in maintaining balance and in the development of proper training programs aimed at improving postural stability in older individuals.

Passive Stiffness and Maximal and Explosive Strength Responses After an Acute Bout of Constant-Tension Stretching.

CONTEXT: Constant-tension (CT) stretching has been used to reduce hamstrings passive stiffness; however, the time course of hamstrings stiffness responses during a short bout of this type of stretching and the effects on maximal and explosive strength remain unclear. OBJECTIVE: To examine the time course of hamstrings passive-stiffness responses during a short, practical bout of manual straight-legged-raise (SLR) CT passive stretches and their effects on maximal and explosive strength in healthy young women. DESIGN: Descriptive laboratory study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Eleven healthy women (age = 24 ± 4 years, height = 167 ± 4 cm, mass = 65 ± 8 kg) participated. INTERVENTION(S): Participants underwent four 15-second SLR CT passive stretches of the hamstrings. MAIN OUTCOME MEASUREMENT(S): Hamstrings passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle-torque curves generated before and after the stretching intervention and at the beginning of each 15-second stretch. Hamstrings peak torque and rate of torque development were derived from maximal voluntary isometric contractions performed before and after the stretching intervention. RESULTS: The slope coefficients (collapsed across phase) for the third and fourth stretches and the poststretching assessment were lower than the prestretching assessment (P range = .004-.04), but they were not different from each other (P > .99). In addition, no differences in peak torque (t10 = -0.375, P = .72) or rate of torque development (t10 = -0.423, P = .68) were observed between prestretching and poststretching. CONCLUSIONS: A short bout of SLR CT passive stretching may effectively reduce hamstrings stiffness without negatively influencing maximal and explosive strength.