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

Age-related time course effects of constant-angle and constant-torque stretching on the passive resistive properties of the posterior hip and thigh muscles in young and old men

The purpose of the present study was to examine the acute effects of static stretching at a constant angle (CA) and constant torque (CT) on the passive resistive properties of the posterior hip and thigh muscles in young and old men. Twenty young (mean±SD: age = 24.60 ± 2.98 years) and seventeen old (age = 71.88 ± 3.86 years) men performed 16, 30-s bouts of CA and CT stretching of the posterior hip and thigh muscles using an instrumented straight-leg raise (SLR). SLRs were then performed again at 10, 20, and 30 min following the completion of the stretching protocol. During each SLR, passive stiffness, passive torque, and electromyographic (EMG) amplitude were determined at the second to last common joint angle of the angle-torque curve, and maximum range of motion (ROM) was determined as the point of discomfort but not pain, as indicated by the participant. Three-way mixed factorial ANOVAs (group [young vs. old] x treatment [CA vs. CT] x time [stretch 1 vs. stretch 2 vs. stretch 4 vs. stretch 8 vs. stretch 16 vs. Post10 vs. Post20 vs. Post30]) were used to analyze all passive resistive variables. The present findings revealed that the older men had greater passive stiffness values compared to the young men. No differences were observed between the CA and CT treatments across stretches for passive torque and ROM; however, differential time course effects were observed between treatments for passive stiffness. The CT treatment decreased passive stiffness following one 30-s bout of stretching, whereas for the CA treatment, passive stiffness did not decrease until stretch 8 (4 min of stretching). Moreover, during the first 4 min of stretching, greater reductions in passive stiffness were observed for the CT treatment than the CA treatment. Both treatments showed lower passive stiffness and torque and higher ROM at Post10, Post20, and Post30 for both age groups; however, the old men exhibited significantly greater changes for these variables compared to the young men when collapsed across treatment and time. These findings may have important stretch-related performance and injury risk implications for a variety of populations and settings

Effects of Practical Durations of Stretching on Hamstrings Range of Motion and Strength

ABSTRACT Stretching is often performed prior to exercise with the intent to improve range of motion (ROM) and athletic performance. However, stretching-induced strength loss has been extensively reported and is believed to be influenced by several factors, including the time under stretch. The majority of previous studies showing stretching-induced strength declines have used stretching routines for durations (8-30 min) considerably longer than those commonly applied in the field. Fewer studies have examined the effects of shorter, more practical durations (≤2 min) of stretching on ROM and muscle strength. PURPOSE: To examine the acute effects of practical stretching durations on hamstrings ROM and muscle strength. METHODS: Eighteen young, healthy females (age = 21±2 years) volunteered for this investigation.Participants visited the laboratory 5 times, separated by 2-7 days at approximately the same time of day (±2 hours). The first visit was a familiarization trial, and the next 4 visits were experimental trials in a randomized order: ((a) control condition and stretching treatment conditions for (b) 30 s, (c) 1 min, and (d) 2 min). For each experimental trial, participants completed 2 passive straight-leg raises (SLRs) and isometric maximal voluntary contractions (MVCs) before and after the treatment condition using an isokinetic dynamometer. The control condition consisted of quiet resting for 5 min. For the SLR assessments, the dynamometer lever arm passively moved the right leg toward the head at 5°·s-1 until the maximal tolerable torque threshold was achieved, which was regarded as the maximum ROM, at which point the leg was immediately returned to the baseline position. For each MVC, participants laid supine and were instructed to extend the right thigh “as hard and fast as possible” 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. The stretching treatments were performed in the same fashion as the SLR assessments; however, when the maximal tolerable torque threshold was reached, it was sustained for 30 s and then released for 20 s. Each stretch was repeated until the specific time under stretch was completed for each condition. RESULTS: ROM increased from pre- to post-stretching for the 30 s(100±21° to 108±22°; P \u3c 0.001), 1 min (100±23º to 109±19º; P \u3c 0.001), and 2 min (103±22º to 113±22º; P \u3c0.001) conditions but not for the control condition (101± 25º to 102± 25º; P = 0.389). PT decreased from pre- to post-stretching for all conditions (collapsed across condition: 231±54Nm to 224±54Nm; P = 0.038). CONCLUSION: These findings demonstrated that the stretching durations of 30 s, 1 min, and 2 min resulted in significant increases (8-10%) in ROM. The similar decreases (1-4%) in PT between conditions indicated that these stretching durations for the hamstrings did not alter muscle strength when compared to the control condition. Because stretching routines for long durations of ≥8 min have been shown to elicit significant reductions (\u3e10%) in muscle strength, it may be advantageous for practitioners who are using pre-exercise stretches as a warm-up, to perform them on their athletes for shorter durations similar to those used in the present study (≤2 min)

Reliability and Relationships between Rectus Femoris Muscle Size and Hip Flexion Maximal and Explosive Strength

Ultrasound assessments of muscle cross-sectional area (CSA) are commonly used to evaluate muscle size in young adults. It has been hypothesized that the CSA of the rectus femoris (RF) may be an important contributor to hip flexion maximal and explosive strength capacities. However, limited data exist regarding the reliability of RF CSA and how it relates to maximal and explosive strength of the hip flexors in young adults. PURPOSE: To examine the reliability of RF CSA and its relationships with hip flexion isometric maximal and explosive strength. METHODS: Nineteen young, healthy females (age = 21±2 years; mass = 61±7 kg; height = 163±6 cm) volunteered for this study. Participants visited the laboratory 2 times, separated by 2-7 days at approximately the same time of day (±2 hours). During each visit, participants underwent 2 diagnostic ultrasound assessments followed by 2 isometric maximal voluntary contractions (MVCs) of the hip flexors using an isokinetic dynamometer. CSA (cm2) of the RF was measured on the right leg using a portable B-mode ultrasound imaging device and linear-array probe. For each ultrasound assessment, participants laid supine with the knee resting comfortably in extension near the natural resting position of 10°. All ultrasound images were taken in the transverse plane using a panoramic ultrasound imaging technique, which consisted of the investigator moving the probe manually at a slow and continuous rate along the surface of the skin from the lateral to medial sides of the muscle. For each MVC, participants laid supine and were instructed to flex the right thigh “as hard and fast as possible” for 3-4 s. Isometric MVC peak torque (PT; Nm) was determined as the highest mean 500 ms epoch during the entire 3-4 s MVC plateau. Rate of torque development (RTD; Nm·s-1) was determined from the linear slope of the torque-time curve over the time interval of 0-200 ms. The intraclass correlation coefficient (ICC) and standard error of measurement expressed as a percentage of the mean (SEM%) were calculated across visits to assess reliability for RF CSA and hip flexion PT and RTD. The relationships between these variables were determined by Pearson product-moment correlation coefficients (r). RESULTS: Mean±SD values (averaged across both visits) were 9.38±1.69 cm2, 136.58±23.88 Nm, and 772.86±170.91 Nm·s-1, ICCs were 0.95, 0.90, and 0.82, and SEM% values were 5.85, 5.68, and 10.03% for the CSA, PT, and RTD data, respectively. Significant positive relationships were observed between CSA and PT (r = 0.605, P = 0.006) and RTD (r = 0.462, P = 0.046). CONCLUSION: These findings demonstrated that CSA, PT, and RTD may be reliable measures for assessing RF muscle size and maximal and explosive strength capacities of the hip flexors in young, healthy adults. The significant relationships observed between CSA and PT and RTD perhaps suggest that the size of the RF may play an important role in hip flexion maximal and explosive strength. As a result, practitioners may consider implementing training programs aimed at increasing the size of the RF in younger adults which may be beneficial for improving the maximal and explosive strength capacities of the hip flexors

Relationship between Vertical Jump Height and Pennation Angle of the Rectus Femoris and Vastus Lateralis

Ultrasound assessments of pennation angle (PA) are commonly used to examine muscle architecture in young adults. Pennation of the lower-body musculature has been suggested to be an important predictor of functional performances for strength-related activities. However, limited data exist regarding how PA is associated with performance during a vertical jump test. PURPOSE: The purpose of this study was to determine the relationship between vertical jump height and PA of the rectus femoris (RF) and vastus lateralis (VL) muscles in healthy, young females. METHODS: Seventeen healthy, young females (age = 22 ± 3 years; mass = 61 ± 8 kg; height = 162 ± 6 cm) volunteered for this study. Participants visited the laboratory two times, separated by seven days at approximately the same time of day (±2 hours). During the first visit, participants were familiarized with the jumping procedures and underwent two diagnostic ultrasound assessments of the RF and VL muscles using a portable B-mode ultrasound imaging device and linear-array probe. During the second visit, participants performed three countermovement vertical jumps using a jump mat, which measured jump height (cm) based on flight time. All ultrasound images were scanned on the right leg with the probe oriented in the longitudinal plane. RF images were taken on the line at the midpoint between the anterior superior iliac spine and the proximal border of the patella. VL images were taken on the line at the midpoint between the greater trochanter and lateral epicondyle of the femur. For each scan, participants laid supine with the knee resting comfortably in extension, while the investigator (A.C.C.) placed the probe on the marked site to capture images of muscle pennation. Muscle fiber PA (°) was determined as the intersection of the fascicles with the deep aponeurosis. Each image was assessed three times, and the average value for PA was used for analysis. Pearson product-moment correlation coefficients (r) were used to examine the relationships between RF and VL PA and vertical jump height. RESULTS: PA values (mean ± SD) were 13.65 ± 3.25°for the RF and 20.53 ± 2.62°for the VL. Jump height was 34.90 ± 4.14 cm. There was a significant positive relationship between jump height and VL PA (r = 0.603, P = 0.010); however, there was no relationship between jump height and RF PA (r = 0.190, P = 0.466). CONCLUSION: The present findings of a significant positive relationship between jump height and VL PA suggest that pennation of the muscle fibers in the VL may play an important role in vertical jump performance. Strength and conditioning coaches and other practitioners may use these findings to help predict explosive jump-related capacities in college-aged females. Moreover, these findings highlight the need for training programs focused on increasing VL PA, as this may be helpful for improving vertical jump height in younger adults

Relationship between Vertical Jump Height and Muscle Size and Quality of the Rectus Femoris and Vastus Lateralis

Ultrasound assessments of muscle cross-sectional area (CSA) and echo intensity (EI) are commonly used to examine muscle size and quality in younger adults. Greater muscle CSA and lower EI values of the rectus femoris (RF) and vastus lateralis (VL) have been associated with improvements in lower-body muscle power and consequently, may play a significant role in the maximum height achieved during a vertical jump test. PURPOSE: To examine the relationships between vertical jump height and CSA and EI of the RF and VL muscles in healthy, young females. METHODS: Seventeen young females (age = 22 ± 3 years; mass = 61 ± 8 kg; height= 162 ± 6 cm) volunteered for this study. Participants visited the laboratory two times, separated by 7 days, at approximately the same time of day (±2 hours). During the first visit, participants were familiarized with the jumping procedures and underwent 2 diagnostic ultrasound assessments of the RF and VL muscles using a portable B-mode ultrasound imaging device and linear-array probe. During the second visit, participants performed 3 countermovement vertical jumps using a jump mat, which measured jump height (cm) based on flight time. All ultrasound images were scanned on the right leg with the probe oriented in the transverse plane. RF images were taken at 50% of the distance between the anterior superior iliac spine and the proximal border of the patella. VL images were taken at the midpoint between the greater trochanter and lateral epicondyle of the femur. For each scan, participants laid supine with the knee resting comfortably in extension, while the investigator (A.C.C.) moved the probe manually at a slow and continuous rate along the surface of the skin from the lateral to the medial sides of the muscle using a panoramic ultrasound imaging technique. Images were analyzed by determining a region of interest consisting of as much of the muscle as possible without any surrounding bone or fascia. CSA (cm2) and EI (AU) were measured from the same region of interest using a quantitative gray-scale analysis (black = 0, white = 255). Pearson product-moment correlation coefficients (r) were used to examine the relationships between RF and VL CSA and EI and vertical jump height. RESULTS: CSA and EI values (mean ± SD) were 9.61 ± 2.60 cm2 and 70.89 ± 8.12 AU for the RF and 21.85 ± 4.71 cm2 and 68.59 ± 6.69 AU for the VL, respectively. Jump height was 34.90 ± 4.14 cm. There was a significant positive relationship between jump height and VL CSA (r = 0.525, P = 0.030); however, there were no relationships between jump height and VL EI (r = -0.140, P = 0.592), RF CSA (r = 0.324, P = 0.204), and RF EI (r = -0.126, P = 0.629). CONCLUSION: The present findings of a significant positive relationship between jump height and VL CSA suggest that muscle size of the VL may play an important role in vertical jump performance. These findings highlight the need for training programs aimed to increase the size of the VL, as this may be beneficial for improving vertical jump height in younger adults

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 \u3c 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

Handgrip Peak Force and Rate of Force Development Measurements: Are They Reliable and Do They Correlate with Vertical Jump Power?

Handgrip peak force and rate of force development (RFD) measurements have been shown to be effective parameters 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 vertical jump (VJ) peak power remains uncertain. PURPOSE: The purpose of this study was to examine the reliability of handgrip peak force and RFD measurements. A secondary aim was to determine if these measurements are correlated with the peak power produced during a VJ test. METHODS: Twenty young, healthy women (age = 21 ± 3 years) volunteered for this study. Participants reported for testing on two different occasions, separated by 2-7 days at approximately the same time of day (± 2 hours). For each testing session, participants completed three VJs followed by three handgrip maximal voluntary contraction (MVC) assessments with the dominant hand. VJs were performed using a linear velocity transducer that was attached to the posterior portion of a belt fastened around the participants’ waistline. For all VJs, participants were instructed to jump up as explosively as possible with both feet at the same time and land on the floor in the starting position. Prior to the VJ assessments, each participant\u27s body mass was entered into the linear velocity transducer microcomputer. Estimated peak power output was calculated in watts (W) and displayed by the microcomputer at the conclusion of each jump. Handgrip MVCs were performed using a novel strength testing device. This device consisted of a microcomputer and a load cell that was equipped with two semi-cylindrical handles for gripping. For each MVC, participants sat in an upright position and were instructed to squeeze the handles of the load cell “as hard and fast as possible” for 3-4 seconds. Handgrip peak force, peak RFD, and RFD at 0-100 (RFD100) and 0-200 (RFD200) milliseconds from contraction onset were calculated and displayed by the device at the conclusion of each assessment. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated between sessions to assess the reliability of handgrip peak force and RFD variables. The relationships between these variables and VJ peak power were determined by Pearson correlation coefficients (r). RESULTS: Handgrip peak force, peak RFD, RFD100, and RFD200 were highly consistent between sessions, with ICCs ranging between 0.89 and 0.92 and CV values between 4.9 and 6.4%. There were significant correlations between VJ peak power and handgrip peak force (r = 0.612, P = 0.004), peak RFD (r = 0.731, P \u3c 0.001), RFD100 (r = 0.671, P = 0.001), and RFD200 (r = 0.701, P = 0.001). CONCLUSION: The results of this study showed that peak force, peak RFD, RFD100, and RFD200 were reliable measures for assessing handgrip strength in young, healthy adults. These measurements were significantly correlated with VJ peak power and thus, could be effective parameters at predicting lower-body explosiveness. The predictive capacity of such parameters to determine a person’s peak power may be important in the early stages of rehabilitation, especially if that person is unable to perform a VJ test

Age-related Differences in Handgrip Strength Characteristics and Vertical Jump Performance

Handgrip strength characteristics, such as peak force and rate of force development (RFD), have been shown to be significantly associated with the performance capacities of the lower-body musculature. Declines in lower-body performance are commonly reported as a consequence of aging. However, few studies have investigated the influence of age on handgrip peak force and RFD. PURPOSE: The purpose of this study was to examine age-related differences in handgrip peak force and RFD between young and older women and the relationships of these characteristics with lower-body performance during a vertical jump (VJ) test. METHODS: Twenty young (age = 21 ± 3 years) and twenty older (67 ± 5 years) healthy women completed three VJs followed by three handgrip maximal voluntary contraction (MVC) assessments with the dominant hand. All VJs were performed on a jump mat. The jump mat assessed lower-body performance by measuring VJ height (cm). Handgrip MVCs were performed using a novel strength testing device. This device consisted of a microcomputer and a load cell that was equipped with two semi-cylindrical handles for gripping. For each MVC, participants sat in an upright position and were instructed to squeeze the handles of the load cell “as hard and fast as possible” for 3-4 seconds. Handgrip peak force, peak RFD, and RFD at 0-100 (RFD100) and 0-200 (RFD200) milliseconds from contraction onset were calculated and displayed by the device at the conclusion of each MVC and were normalized to body mass. Independent samples t-tests were used to compare VJ height and handgrip peak force and RFD characteristics between the young and older women. Pearson correlation coefficients (r) were calculated separately for the young and older women to examine the relationships between VJ height and handgrip peak force and RFD. RESULTS: The older women exhibited significantly lower VJ height (older = 20.3 ± 3.8 cm; young = 34.4 ± 5.9 cm; P \u3c 0.001), peak force (older = 2.4 ± 0.4 N·kg-1; young = 2.7 ± 0.5 N·kg-1; P = 0.028), peak RFD (older = 13.6 ± 2.6 N·s-1·kg-1; young = 16.4 ± 2.9 N·s-1·kg-1; P = 0.003), RFD100 (older = 13.2 ± 3.0 N·s-1·kg-1; young = 15.7 ± 3.3 N·s-1·kg-1; P = 0.016), and RFD200 (older = 9.3 ± 1.6 N·s-1·kg-1; young = 10.8 ± 1.6 N·s-1·kg-1; P = 0.003) than the younger women. Positive correlations were observed between VJ height and handgrip RFD200 (r = 0.502, P = 0.024) and peak RFD (r = 0.453, P = 0.045) for the younger women. Positive correlations were also observed between VJ height and handgrip RFD200 (r = 0.446, P = 0.049) and peak RFD (r = 0.408, P = 0.074) for the older women, although the latter correlation did not reach statistical significance. There were no significant correlations between VJ height and handgrip peak force (young: r = 0.389, P = 0.090; older: r = 0.311, P = 0.183) or RFD100 (young: r = 0.366, P = 0.113; older: r = 0.382, P = 0.096) for either age group. CONCLUSION: These findings demonstrated that VJ height and handgrip peak force and RFD characteristics decrease in old age. The significant correlations observed between VJ height and RFD200 in the young and older women suggest that handgrip rapid strength (0-200 milliseconds) may be an effective predictor of one’s jumping ability

Reliability and Relationships between Supine Medicine Ball Throw Kinetics and Vertical Jump Height

Supine medicine ball throw (SMBT) assessments have been used previously to evaluate upper-body explosive strength in young adults. Kinetic variables, such as peak force and rate of force development (RFD), can be measured during a SMBT. These variables have been suggested to be important predictors of athletic performance capacities. However, limited data exist regarding the reliability of SMBT peak force and RFD measurements and how they associate with performance during a vertical jump (VJ) test. PURPOSE: The purpose of this study was to examine the reliability of SMBT variables and their relationship with VJ height. METHODS: Twenty young, healthy women (age = 21 ± 3 years) volunteered for this study. Participants reported for testing on two different occasions, separated by 2-7 days at approximately the same time of day (± 2 hours). For each testing session, participants completed three VJs followed by three SMBT assessments. All VJs were performed on a jump mat. The jump mat measured VJ height (cm) based on flight time. For the SMBTs, participants laid on a force plate in the supine position with their hands on the ball (2.7 kg) and knees and hips flexed at 90º. Participants were instructed to throw the ball explosively upward with as much force as possible, using a motion similar to a basketball chest pass. The vertical force signal (N) from the force plate was recorded during each throw and used to measure peak force and RFD variables. Peak force was calculated as the highest force value. RFDmax was calculated as the highest slope for any 20 ms epoch that occurred over the rising portion of the force signal. RFD30% and RFD40-80% were calculated as the linear slope of the force signal from the onset of the throw to 30% peak force and from 40% to 80% peak force, respectively. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated between sessions to assess the reliability of SMBT peak force and RFD variables. The relationships between these variables and VJ height were assessed by Pearson correlation coefficients (r). RESULTS: The ICC for SMBT RFD30% was 0.55. This ICC was considerably lower than the ICCs for the other SMBT variables (0.82-0.88). The CV value for SMBT RFD30% was 27.2%, whereas the CV values for SMBT peak force, RFDmax, and RFD40-80% were all less than or equal to 14.0%. There were significant relationships between VJ height and SMBT peak force (r = 0.483, P = 0.031), RFDmax (r = 0.484, P = 0.031), and RFD40-80% (r = 0.491, P = 0.028); however, there was no significant relationship between VJ height and RFD30% (r = 0.359, P = 0.120). CONCLUSION: The results of this study demonstrated that SMBT peak force, RFDmax, and RFD40-80% were reliable measures for assessing upper-body explosive strength in young, healthy adults. These measurements were significantly associated with VJ height and therefore, may be effective parameters at predicting a person’s jumping ability and overall athletic performance potential. RFD30% was unreliable and not significantly correlated with VJ height. As a result, this variable should not be used as a performance measure when conducting SMBT assessments