Acute Effects of Static Stretching on Passive Stiffness of the Hamstrings in Healthy Young and Older Women

Static stretching is often performed prior to exercise to increase range of motion (ROM) and reduce passive stiffness of the muscle-tendon unit. A decrease in passive stiffness after stretching is believed to reduce the risk of injury and improve athletic performance. Previous research has demonstrated that an acute bout of static stretching was effective at decreasing passive stiffness in older men. However, to our knowledge, no previous research has examined the acute effects of static stretching on passive stiffness in older women, nor have there been any studies that have compared these effects with a younger female population. PURPOSE: The purpose of this study was to investigate the acute effects of static stretching on passive stiffness of the hamstrings in healthy young and older women. METHODS: Fifteen young (23 ± 4 years) and 15 older (73 ± 5 years) healthy women underwent two passive knee extension assessments before (Pre) and after (Post) two randomized conditions that included a control treatment (quiet resting for two min) and an experimental treatment of static stretching. During the passive knee extension, participants were seated in an upright position with restraining straps placed over the shoulders and right thigh. Each knee extension assessment was administered using a calibrated isokinetic dynamometer programmed in passive mode to extend the leg at 5°∙s-1. All passive knee extensions were performed on the right leg to the point of discomfort but not pain as indicated by the participant, which was regarded as the maximum ROM. Once maximum ROM was reached, the leg was then immediately returned to the baseline position, which was a knee joint angle of 80° below full extension. Passive stiffness (Nm·º-1) was calculated during each knee extension assessment as the final slope of the tangent to the angle-torque curve. For the experimental treatment, four 15-s static stretches were completed in the same manner as the passive knee extension assessments; however, when maximum ROM was reached, the leg was held at this position for 15 s. Each 15-s stretch was separated by 15 s of rest. RESULTS: Passive stiffness (collapsed across group) was lower (P = 0.007) at Post (0.63 ± 0.18 Nm·º-1) compared to Pre (0.72 ± 0.18 Nm·º-1) for the stretching treatment. There was no significant difference (P \u3e 0.999) in passive stiffness between the Pre (0.72 ± 0.18 Nm·º-1) and Post (0.74 ± 0.28 Nm·º-1) time points for the control. The stretch-induced decrease in passive stiffness from Pre to Post was significantly greater (P = 0.049) for the old (-17%) compared to the younger (-5%) women. CONCLUSION: These findings showed that passive stiffness in young and older women decreased after four 15-s static stretches. The greater stretch-induced decrease in passive stiffness observed for the older women suggests that an acute bout of static stretching may be particularly beneficial for alleviating muscle tightness in the elderly. As a result, it may be advantageous for older adults to incorporate static stretching into their warm-up routine prior to exercise, as this may be used to reduce passive stiffness, which could help improve performance and reduce the risk of injury in this population

Relationships between Walking Speed and Lower Extremity Muscle Quality and Strength in Elderly Females

The link between walking speed, rectus femoris (RF) muscle quality [echo intensity (EI)], and maximal and rapid strength in older adults is not well understood. PURPOSE: To examine the relationships between walking speed, RF EI, and maximal and rapid isometric torque characteristics of the leg extensors in elderly females. METHODS: Twenty elderly females (age = 67 ± 4 years; height = 159 ± 6 cm; mass = 68 ± 7 kg) underwent one diagnostic ultrasound assessment followed by three isometric maximal voluntary contractions (MVC) of the leg extensors and a 6-min walk test. RF EI was measured on the right leg using a portable B-mode ultrasound imaging device and linear-array probe. Walking speed was determined as the average speed during the 6-min walk test. For each MVC, participants sat in an upright position and were instructed to push “as hard and fast as possible” against a load cell for 3-4 s. Isometric MVC peak torque (PT) was determined as the highest mean 500 ms epoch during the entire 3-4 s MVC plateau. Peak rate of torque development (RTD) was calculated during each MVC as the highest slope value for any 50 ms epoch that occurred over the initial 200 ms of the torque-time curve. Pearson correlation coefficients (r) were used to examine the relationships between walking speed, EI, PT, and RTD. A partial correlation was used to examine the relationship between walking speed and RTD when controlling for EI. RESULTS: Mean ± SD values were 1.55 ± 0.23 m/s for walking speed, 144.16 ± 19.48 AU for EI, 107.62 ± 23.79 Nm for PT, and 872.35 ± 365.16 Nm/s for RTD. There were significant relationships between walking speed and RTD (r = 0.451; P = 0.046) and EI (r = -0.497; P = 0.026). There was a significant negative relationship between EI and RTD (r = -0.469; P = 0.037). No significant relationships were observed between PT and walking speed (r = 0.394; P = 0.085) or EI (r = -0.413; P = 0.071). With EI as a control variable, there was no significant relationship between walking speed and RTD (r = 0.285; P = 0.238). CONCLUSION: We found a significant positive relationship between walking speed and RTD of the leg extensors in elderly females. Although the reason for this is uncertain, partial correlation analysis suggested that this relationship may be explained by the variance shared (collinearity) between walking speed and RF EI. From a functional standpoint, an age-related decrease in RTD due to its apparent collinearity with RF EI, may significantly impact the quality of life among older adults by impairing their ability to perform important time-dependent movement tasks (i.e., walking fast to catch the bus or train, quickly crossing the street to avoid oncoming traffic, etc.). Consequently, given the influence of EI on RTD, it is possible that training programs used to improve muscle quality may also be used to help improve rapid strength, which could be beneficial for increasing walking speed as well as a multitude of other functional performance abilities in the elderly

Sex-related Differences in Maximal and Rapid Hamstrings to Quadriceps Strength Capacities

The balance between leg flexor and extensor strength, which is typically assessed using the hamstrings to quadriceps (H/Q) strength ratio, has been implicated as an important factor in the kneejoint stability of younger populations. Sex differences in hamstrings and quadriceps maximal and rapid strength are commonly reported between young men and women; however, few studies have investigated the influence of sex on maximal and rapid strength H/Q ratios. PURPOSE: To examine sex-related differences in maximal and rapid strength H/Q ratios between college-aged men and women. METHODS: Ten physically-active men (age = 23 ± 3 years; height = 177 ± 5 cm; mass = 82 ± 8 kg) and 10 physically-active women (age = 22 ± 3 years; height = 165 ± 9 cm; mass = 66 ± 7 kg) performed three isometric maximal voluntary contractions (MVCs) of the leg extensors and flexors on a calibrated isokinetic dynamometer. For each MVC, participants sat in an upright position and were instructed to extend or flex the leg “as hard and fast as possible”for 3-4 seconds. Maximal and rapid isometric H/Q strength ratios were determined by taking the quotients between leg flexor and extensor peak torque (PT H/Q) and rate of torque development(RTD H/Q). Independent samples t-tests were used to compare demographic characteristics and PT and RTD H/Q ratios between the men and women. RESULTS: The men were taller (P = 0.002) and weighed more (P \u3c 0.001) than the women. The women exhibited a lower RTD H/Q ratio (women = 0.44 ± 0.08; men = 0.54 ± 0.11; P= 0.027) than the men; however, there was no significant difference between the men and women for PT H/Q (women = 0.55 ± 0.09; men = 0.57 ± 0.11; P= 0.576). CONCLUSION: These findings demonstrated that the rapid strength H/Q ratio was significantly lower in the women than the men, while no difference was observed for the maximal strength H/Q ratio. Because a deficit in hamstrings to quadriceps rapid strength may decrease one’s ability to stabilize the knee joint during explosive-type activities, it is possible that the sex difference in RTD H/Q ratio found in the present study may be a significant contributor to the high prevalence of knee-related injuries that are often observed in physically-active women. As such, lower-extremity muscle strengthening programs with an emphasis on explosive power training (particularly for the hamstrings muscles) may be warranted as a preventative measure for women who are highly susceptible to physical-activity induced injuries involving the knee

Relationships between Functional Performance and Quadriceps Muscle Size and Quality in Healthy Older Women

Ultrasound assessments of quadriceps cross-sectional area (CSA) and echo intensity (EI) are commonly used to evaluate lower-body muscle size and quality in older adults. It has been hypothesized that muscle CSA and EI of the quadriceps may be important predictors of functional performances such as gait speed and vertical jump power. However, limited data exist regarding how these parameters associate with performance during a timed up-and-go (TUG) task. PURPOSE: The purpose of this study was to examine the relationships between TUG performance and muscle CSA and EI of the quadriceps in older women. METHODS: Twenty healthy older women (mean ± SD; age = 67 ± 4 years; body mass = 68 ± 7 kg; height = 159 ± 6 cm) volunteered to participate in this study. TUG performance was measured as the time (sec) taken to rise from a chair, walk three meters, return, and sit down. Panoramic ultrasound images of the vastus lateralis (VL) and rectus femoris (RF) were obtained on the right thigh to determine CSA and EI for each muscle. The CSAs (cm2) for the VL and RF were added together and normalized to body mass (kg) to provide a relative measure of quadriceps CSA (cm2/kg). Quadricep EI (AU) was determined as the average of the EIs for the VL and RF. Pearson correlation coefficients (r) were used to examine the relationships between TUG performance and quadriceps CSA and EI. RESULTS: TUG performance (mean ± SD) was 8.25 ± 1.39 sec, CSA was 0.22 ± 0.04 cm2/kg, and EI was 137.37 ± 23.43 AU. There was a significant positive relationship between TUG and EI (r = 0.509; P = 0.022) and a significant negative relationship between TUG and CSA (r = -0.546; P = 0.013).CONCLUSION: The present findings of significant relationships between TUG and CSA and EI suggest that muscle size and quality of the quadriceps may be characteristics relevant to mobility in older adults. Researchers and practitioners may use these findings as ultrasound screening tools to help predict the TUG performance capacities of older populations. Additionally, these findings highlight the importance of developing training programs aimed at increasing quadriceps muscle size and quality, as these changes may be beneficial for improving TUG as well as a multitude of other functional performance abilities in older adults

Vertical Jump Performance as a Discriminator of Playing Ability in Collegiate Female Soccer Players

Previous studies have assessed the importance of physical characteristics to soccer playing ability by comparing performance-based outcomes between starters and non-starters. Starters are often considered the most skilled players on the team. These players get more playing time than non-starters and have been shown to achieve higher performance outcomes on intermittent fitness tests. However, it remains unclear whether starters can achieve higher performance outcomes on a countermovement vertical jump. PURPOSE: The purpose of this study was to investigate the efficacy of countermovement vertical jump height and peak power to discriminate between starters and non-starters in collegiate female soccer. METHODS: Twenty-seven collegiate female soccer players (age = 19.56 ± 1.28 years; height = 164.26 ± 5.74 cm; body mass = 66.65 ± 8.43 kg) were recruited to participate in the present study. All testing was completed during the 2021 preseason training period. The players were classified as starters (n = 12) or non-starters (n = 15) according to their average number of minutes played per game during the subsequent exhibition season. Each participant reported to the laboratory for a single visit where they performed three countermovement vertical jump tests on a jump mat. For each jump, participants stood on the mat with feet shoulder width apart and hands positioned on the hips. Participants were not allowed to take any steps prior to performing the vertical jump and a quick descending quarter-squat countermovement was allowed before the ascending takeoff phase. The participants were instructed to jump as explosively as possible with both feet at the same time and land on the jump mat in the starting position. Vertical jump height (cm) was estimated from the flight time recorded by the jump mat. Peak power output was estimated using a previously validated regression equation: peak power (W) = 51.9 × vertical jump height (cm) + 48.9 × body mass (kg) - 2007. Independent samples t-tests were used to compare vertical jump height and peak power between the starting and non-starting groups. RESULTS: Vertical jump height was significantly greater (P = 0.039) for the starters (38.60 ± 6.11 cm) compared to the non-starters (34.43 ± 3.75 cm). There was no significant difference (P = 0.448) between the starters (3076.72 ± 331.98 W) and non-starters (3182.23 ± 369.67 W) for peak power. CONCLUSION: These findings suggest that vertical jump height is an effective measure for discriminating between starters and non-starters in collegiate female soccer. Vertical jump characteristics are critical to a player’s performance on the field. Because the starters in this study were able to jump higher than the non-starters, vertical jump height may be an important parameter for identifying players with a high degree of soccer playing ability

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 \u3c 0.001). Movement time and EI values were lower (P ≤ 0.004) and RSI values were higher (P \u3c 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