Thermoregulation and Hydration in Female American Football Players During Practices.

ABSTRACT: Lopez, RM, Ashley, CD, Zinder, SM, and Tritsch, AJ. Thermoregulation and hydration in female American football players during practices. J Strength Cond Res 35(9): 2552-2557, 2021-Little is known about hydration practices and thermoregulation in female tackle football players. The purpose of the study was to examine the thermoregulatory and hydration responses of female professional American football players. Fifteen females from the same tackle football team volunteered for this observational field study. Each subject was observed for 4 practices for the following measures: gastrointestinal temperature (TGI), maximum TGI, heart rate (HR), maximum HR (HRmax), fluid consumption, sweat rate, percent body mass loss (%BML), urine specific gravity (USG), urine color (Ucol), perceptual measures of thirst, thermal sensations, and rating of perceived exertion (RPE). Descriptive data (mean ± SD) were calculated for all measures. Main measures were analyzed using a repeated-measures analysis of variance. Trials took place during evening practices. Average TGI during practices was 38.0 ± 0.3° C while maximum TGI was 38.4 ± 0.3° C (n = 14). Average practice HR was 118 ± 11 b·min-1, while HRmax was 148 ± 13 b·min-1. Subjects arrived at practices with Ucol of 3 ± 1 and USG of 1.018 ± 0.007. Postpractice USG (1.022 ± 0.007) was significantly higher than prepractice across all days (p < 0.001). The average sweat rate across 4 practices was 0.6 ml·h-1. Average %BML was 0.3 ± 0.4%. Thirst and thermal sensations were moderate (4 ± 1 and 5 ± 1, respectively), while RPE was 11 ± 1. Female football players tended to have similar physiological responses to males. Although subjects seemed to adequately match their sweat losses with fluid consumed during practice, there was considerable variability in hydration indices and hydration habits, with some subjects experiencing hypohydration and others overestimating their fluid needs. Those working with this population should emphasize the need for hydration education and establish individualized hydration regimens.

The relationship between spatiotemporal gait asymmetry and balance in individuals with chronic stroke.

Falls are common after stroke and often attributed to poor balance. Falls often occur during walking, suggesting that walking patterns may induce a loss of balance. Gait after stroke is frequently spatiotemporally asymmetric, which may decrease balance. The purpose of this study is to determine the relationship between spatiotemporal gait asymmetry and balance control. Thirty-nine individuals with chronic stroke walked at comfortable and fast speeds to calculate asymmetry ratios for step length, stance time, and swing time. Balance measures included the Berg Balance Scale, step width during gait, and the weight distribution between legs during standing. Correlational analyses determined the relationships between balance and gait asymmetry. At comfortable and fast gait speeds, step width was correlated with stance time and swing time asymmetries (r = 0.39-0.54). Berg scores were correlated with step length and swing time asymmetries (r = -0.36 to -0.63). During fast walking, the weight distribution between limbs was correlated with stance time asymmetry (r = -0.41). Spatiotemporal gait asymmetry was more closely related to balance measures involving dynamic tasks than static tasks, suggesting that gait asymmetry may be related to the high number of falls poststroke. Further study to determine if rehabilitation that improves gait asymmetry has a similar influence on balance is warranted.

Effect of warm-up with different weighted bats on normal baseball bat velocity.

Traditionally, baseball players have used a heavy bat for warm-up before competition. Because bat velocity is an essential component to hitting a baseball, and because players warm up differently, there is a need to investigate the best way to maximize post warm-up bat velocity. The purpose of this study was to determine the effects of warm-up with different weighted bats on normal baseball bat velocity. Nineteen recreational male baseball players (age, 24.5 +/- 3.9 years; height, 181.1 +/- 8.4 cm; body mass, 87.9 +/- 18.4 kg) participated in this study. Three different randomized warm-up conditions were completed and analyzed for velocity and for their effect on post warm-up normal baseball bat velocity. Subjects were instructed to perform 5 maximal swings with each of 3 different weighted bats-light (LB = 9.6 oz), normal (NB = 31.5 oz), and heavy (HB = 55.2 oz)-followed by 30-second rest and then 5 swings of the NB. Analysis of variance revealed that warm-up velocity of the LB (63.57 +/- 3.58 mph) was significantly (p < 0.05) faster than that of NB (51.25 +/- 3.01 mph) and HB (41.79 +/- 3.01 mph), whereas warm-up velocity of NB was also significantly faster than that of HB. For post warm-up, LB (52.29 +/- 2.68 mph) and NB (50.60 +/- 3.04 mph) produced significantly faster velocity of the normal bat than the HB (48.26 +/- 2.98 mph). Warming up with 5 swings of a light or normal bat appears to increase post warm-up velocity of the normal bat when compared with warming up with a heavy bat after a rest period of 30 seconds. Within the bat weight spectrum of this study, it is suggested that when preparing to hit, 5 warm-up swings with either a light or normal bat will allow a player to achieve the greatest velocity of their normal bat.

Acute effects of heavy-load squats on consecutive squat jump performance.

Postactivation potentiation (PAP) and complex training have generated interest within the strength and conditioning community in recent years, but much of the research to date has produced confounding results. The purpose of this study was to observe the acute effects of a heavy-load back squat [85% 1 repetition maximum (1RM)] condition on consecutive squat jump performance. Twelve in-season Division I male track-and-field athletes participated in two randomized testing conditions: a five-repetition back squat at 85% 1RM (BS) and a five-repetition squat jump (SJ). The BS condition consisted of seven consecutive squat jumps (BS-PRE), followed by five repetitions of the BS at 85% 1RM, followed by another set of seven consecutive squat jumps (BS-POST). The SJ condition was exactly the same as the BS condition except that five consecutive SJs replaced the five BSs, with 3 minutes' rest between each set. BS-PRE, BS-POST, SJ-PRE, and SJ-POST were analyzed and compared for mean and peak jump height, as well as mean and peak ground reaction force (GRF). The BS condition's mean and peak jump height and peak GRF increased 5.8% +/- 4.8%, 4.7% +/- 4.8%, and 4.6% +/- 7.4%, respectively, whereas the SJ condition's mean and peak jump height and peak GRF decreased 2.7% +/- 5.0%, 4.0% +/- 4.9%, and 1.3% +/- 7.5%, respectively. The results indicate that performing a heavy-load back squat before a set of consecutive SJs may enhance acute performance in average and peak jump height, as well as peak GRF.

Validity and reliability of a new in vivo ankle stiffness measurement device.

This investigation was designed to test the validity and reliability of a new measure of inversion/eversion ankle stiffness on a unique medial/lateral swaying cradle device utilizing a test/retest with comparison to a known standard. Ankle stiffness is essential to maintaining joint stability. Most ankle injuries occur via an inversion mechanism. To date, very little information is available regarding stiffness of the evertor muscles in the prevention of excessive inversion joint rotation. Transient oscillation data representing inversion/eversion stiffness was obtained in a bipedal weight-bearing stance with an upright posture. Using commercially available springs with stiffness of 4.80N/cm the measured value recorded by the cradle was 4.87N/cm. Mean active stiffness values of the ankle were 35.70Nm/cm (SD 9.45). The trial-to-trial reliability ICC (2,1) coefficient was 0.96 with an SEM of 2.05Nm/rad, and the day-to-day reliability ICC (2,k) coefficient was 0.93 and an SEM of 3.00Nm/rad. The results demonstrate that inversion/eversion ankle stiffness measures on this device are a valid, repeatable and consistent measure. This is relevant because the ability to accurately quantify inversion/eversion ankle stiffness will improve our understanding of biomechanical stability and factors that influence it. It will also enable identification of ankle injury risk factors that will lead to more efficient rehabilitation programs and injury prevention strategies.

The effects of velocity-spectrum training on the ability to rapidly step.

Falls may occur because of a deficiency in the ability to rapidly step in the desired direction. Previous models developed to predict rapid step ability have been based on balance, video analysis, or uniplanar isokinetic performance. The purpose of this investigation was to determine the effects of multiplanar velocity-spectrum training of the hip. Seven males (23.14 years) and 16 females (23.75 years) were tested for peak torque, peak power, and rate of velocity development and on rapid step test (RST) measurements. Participants in the training group went through 8 training sessions over 4 weeks, consisting of unilateral hip flexion/extension and hip abduction/adduction of each leg, while the control group maintained regular activity throughout the 4-week span. Exercises were performed on a Biodex System 3 isokinetic dynamometer beginning at a speed of 60 degrees x sec(-1), gradually increasing in speed every week up to 180, 300, and 400 degrees x s(-1), respectively. Analysis of the data revealed no significant (p < 0.05) differences between groups on any measure. However, the data showed a significant improvement in RST time (pre: 50.87 +/- 4.41 seconds; post: 49.20 +/- 4.28 seconds) and number of errors (pre: 4.13 +/- 2.87 errors; post: 2.75 +/- 1.81 errors), implying that a learning effect took place on the RST for all individuals. Additionally, short-term isokinetic training did not translate into significant results. It was concluded that 4 weeks of velocity-spectrum training of the hip did not lead to improvements on the ability to rapidly step, as measured by the RST. Therefore, the open-kinetic-chain training should not be done for improvements on a functional, closed-kinetic-chain activity.

The effect of single versus multiple sets on strength.

Research has previously been divided on whether performing resistance training with a single set per training session is as effective for increasing strength as training with multiple sets. The purpose of this study was to determine the effect of single sets versus multiple sets on strength. Forty subjects were randomly assigned into 1 of 3 groups: control (C; n = 8), single set (SS; n = 14), or multiple sets (MS; n = 18) to perform 8 maximal knee extensions at 60 degrees .s(-1) on a Biodex System 3 isokinetic dynamometer twice a week for 8 weeks. The SS group performed 1 set while the MS group performed 3 sets. All groups were pre-, mid- (4 weeks), and posttested at 60 degrees x s(-1). Strength was expressed as peak torque (PT). A 3 x 3 x 2 (time x group x sex) mixed factor repeated measures analysis of variance (ANOVA) revealed no interaction involving sex, but there was an interaction of group by time. The MS group exhibited a significant (p < 0.05) increase in PT (pre = 171.39 +/- 61.98 Nm; mid = 193.08 +/- 66.23 Nm) between the pretest and the midtest while the SS (pre = 163.45 +/- 56.37 Nm; mid = 172.60 +/- 61.78 Nm) and C groups (pre = 135.997 +/- 54.31 Nm; mid = 127.66 +/- 53.12 Nm) did not change. Strength did not change between the midtest and the posttest for any group. It was concluded that performing 3 sets of isokinetic knee extensions was more effective than performing a single set for increasing peak torque. These results seem to indicate that for increasing strength of the quadriceps, performing multiple sets is superior to performing a single set of resistance exercise.

Sex differences in valgus knee angle during a single-leg drop jump.

CONTEXT: Sex differences in lower extremity landing mechanics and muscle activation have been identified as potential causative factors leading to the increased incidence of anterior cruciate ligament injuries in female athletes. Valgus knee alignment places greater strain on the anterior cruciate ligament than a more neutral alignment. Gluteus medius (GM) activation may stabilize the leg and pelvis during landing, limiting valgus knee motion and potentially preventing anterior cruciate ligament injury. OBJECTIVE: To determine if frontal-plane knee angle and GM activation differ between the sexes at initial contact and maximal knee flexion during a single-leg drop landing. DESIGN: Between-groups design. SETTING: Motion analysis laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-two healthy subjects between the ages of 18 and 30 years. INTERVENTION(S): The independent variables were sex (male or female) and position (initial contact or maximal knee flexion). MAIN OUTCOME MEASURE(S): Frontal-plane knee angle and GM average root mean square (aRMS) amplitude. RESULTS: At initial contact, women landed in knee valgus and men landed in knee varus (P < .025). At maximal knee flexion, both men and women were in a position of knee varus, but the magnitude of varus was less in women than in men (P < .025). The GM aRMS amplitude was greater at maximal knee flexion than at initial contact (P < .025); however, male GM aRMS did not differ from female GM aRMS amplitude at either position (P > .025). CONCLUSIONS: Women tended to land in more knee valgus before and at impact than men. The GM muscle activation did not differ between the sexes and, thus, does not appear to be responsible for the sex differences in knee valgus. The excessive valgus knee angles displayed in women may help to explain the sex disparity in anterior cruciate ligament injury.

Arthrogenic muscle inhibition in the leg muscles of subjects exhibiting functional ankle instability.

BACKGROUND: Functional ankle instability or a subjective report of ;;giving way'' at the ankle may be present in up to 40% of patients after a lateral ankle sprain. Damage to mechanoreceptors within the lateral ankle ligaments after injury is hypothesized to interrupt neurologic feedback mechanisms resulting in functional ankle instability. The altered input can lead to weakness of muscles surrounding a joint, or arthrogenic muscle inhibition. Arthrogenic muscle inhibition may be the underlying cause of functional ankle instability. Establishing the involvement of arthrogenic muscle inhibition in functional ankle instability is critical to understanding the underlying mechanisms or chronic ankle instability. The purpose of this investigation was to determine if arthrogenic muscle inhibition is present in the ankle joint musculature of patients exhibiting unilateral functional ankle instability. METHODS: Twenty-nine subjects, 15 with unilateral functional ankle instability and 14 healthy control subjects, consented to participate. Bilateral soleus, peroneal, and tibialis anterior H-reflex and M-wave recruitment curves were obtained. Maximal H-reflex and maximal M-wave values were identified and the H:M ratios were calculated for data analysis. Separate 1 x 2 ANOVA were done for both the functional ankle instability and control groups to evaluate differences between limbs on the H:M ratios. Bonferroni multiple comparison procedures were used for post hoc comparisons (p < or = 0.05). RESULTS: The soleus and peroneal H:M ratios for subjects with functional ankle instability were smaller in the injured limb when compared with the uninjured limb (p < 0.05). No limb difference was detected for the tibialis anterior H:M ratio in the functional ankle instability group (p = 0.904). No side-to-side differences were detected for the H:M ratios in patients reporting no history of ankle injury (p > 0.05). CONCLUSIONS: Depressed H:M ratios in the injured limb suggest that arthrogenic muscle inhibition is present in the ankle musculature of patients exhibiting functional ankle instability. Establishing and using therapeutic techniques to reverse arthrogenic muscle inhibition may reduce the incidence of functional ankle instability.

Relationship between two proprioceptive measures and stiffness at the ankle.

Previous research has investigated the role of proprioception and stiffness in the control of joint stability. However, to date, no research has been done on the relationship between proprioception and stiffness. Therefore, the purpose of this study was to determine the relationship between force sense, joint reposition sense, and stiffness at the ankle. A heterogeneous sample was obtained for this study; 20 of the 40 participants had a history of ankle sprains, and 13 of the 20 had been diagnosed by a physician (two mild ankle sprains, seven moderate sprains, four severe sprains). All subjects were asymptomatic and active at the time of the study. Active joint reposition sense was measured using a custom-built ankle goniometer, force sense was measured unilaterally and contralaterally with a load cell, and ankle muscle stiffness was measured via transient oscillation using a custom-built inversion-eversion cradle. We found no significant correlations between stiffness and joint reposition sense, with values of r ranging from 0.01 to 0.21. Significant correlations were found between stiffness and force sense. Specifically, contralateral force sense reproduction was significantly correlated to stiffness in the injured or "involved" ankle (r's ranging from 0.47 to 0.65; P< or =0.008). Whether the decreased ability to appropriately sense force (increased error) sends information to the central nervous system to increase muscle stiffness in response to an unexpected loss of stability, or whether these two phenomena function independently and both change concurrently as a result of injury to the system requires further investigation.

Altered knee and ankle kinematics during squatting in those with limited weight-bearing-lunge ankle-dorsiflexion range of motion.

CONTEXT: Ankle-dorsiflexion (DF) range of motion (ROM) may influence movement variables that are known to affect anterior cruciate ligament loading, such as knee valgus and knee flexion. To our knowledge, researchers have not studied individuals with limited or normal ankle DF-ROM to investigate the relationship between those factors and the lower extremity movement patterns associated with anterior cruciate ligament injury. OBJECTIVE: To determine, using 2 different measurement techniques, whether knee- and ankle-joint kinematics differ between participants with limited and normal ankle DF-ROM. DESIGN: Cross-sectional study. SETTING: Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS: Forty physically active adults (20 with limited ankle DF-ROM, 20 with normal ankle DF-ROM). MAIN OUTCOME MEASURE(S): Ankle DF-ROM was assessed using 2 techniques: (1) nonweight-bearing ankle DF-ROM with the knee straight, and (2) weight-bearing lunge (WBL). Knee flexion, knee valgus-varus, knee internal-external rotation, and ankle DF displacements were assessed during the overhead-squat, single-legged squat, and jump-landing tasks. Separate 1-way analyses of variance were performed to determine whether differences in knee- and ankle-joint kinematics existed between the normal and limited groups for each assessment. RESULTS: We observed no differences between the normal and limited groups when classifying groups based on nonweight-bearing passive-ankle DF-ROM. However, individuals with greater ankle DF-ROM during the WBL displayed greater knee-flexion and ankle-DF displacement and peak knee flexion during the overhead-squat and single-legged squat tasks. In addition, those individuals also demonstrated greater knee-varus displacement during the single-legged squat. CONCLUSIONS: Greater ankle DF-ROM assessed during the WBL was associated with greater knee-flexion and ankle-DF displacement during both squatting tasks as well as greater knee-varus displacement during the single-legged squat. Assessment of ankle DF-ROM using the WBL provided important insight into compensatory movement patterns during squatting, whereas nonweight-bearing passive ankle DF-ROM did not. Improving ankle DF-ROM during the WBL may be an important intervention for altering high-risk movement patterns commonly associated with noncontact anterior cruciate ligament injury.

Hamstrings Stiffness and Landing Biomechanics Linked to Anterior Cruciate Ligament Loading.

CONTEXT: Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. OBJECTIVE: To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. DESIGN: Cross-sectional study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). INTERVENTION(S): Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. MAIN OUTCOME MEASURE(S): Hamstrings stiffness was normalized to body mass (N/m·kg-1). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. RESULTS: Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729-2.224, P < .05). CONCLUSIONS: Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.

Hamstrings stiffness and landing biomechanics linked to anterior cruciate ligament loading.

CONTEXT: Greater hamstrings stiffness is associated with less anterior tibial translation during controlled perturbations. However, it is unclear how hamstrings stiffness influences anterior cruciate ligament (ACL) loading mechanisms during dynamic tasks. OBJECTIVE: To evaluate the influence of hamstrings stiffness on landing biomechanics related to ACL injury. DESIGN: Cross-sectional study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 36 healthy, physically active volunteers (18 men, 18 women; age = 23 ± 3 years, height = 1.8 ± 0.1 m, mass = 73.1 ± 16.6 kg). INTERVENTION(S): Hamstrings stiffness was quantified via the damped oscillatory technique. Three-dimensional lower extremity kinematics and kinetics were captured during a double-legged jump-landing task via a 3-dimensional motion-capture system interfaced with a force plate. Landing biomechanics were compared between groups displaying high and low hamstrings stiffness via independent-samples t tests. MAIN OUTCOME MEASURE(S): Hamstrings stiffness was normalized to body mass (N/m·kg(-1)). Peak knee-flexion and -valgus angles, vertical and posterior ground reaction forces, anterior tibial shear force, internal knee-extension and -varus moments, and knee-flexion angles at the instants of each peak kinetic variable were identified during the landing task. Forces were normalized to body weight, whereas moments were normalized to the product of weight and height. RESULTS: Internal knee-varus moment was 3.6 times smaller in the high-stiffness group (t22 = 2.221, P = .02). A trend in the data also indicated that peak anterior tibial shear force was 1.1 times smaller in the high-stiffness group (t22 = 1.537, P = .07). The high-stiffness group also demonstrated greater knee flexion at the instants of peak anterior tibial shear force and internal knee-extension and -varus moments (t22 range = 1.729-2.224, P < .05). CONCLUSIONS: Greater hamstrings stiffness was associated with landing biomechanics consistent with less ACL loading and injury risk. Musculotendinous stiffness is a modifiable characteristic; thus exercises that enhance hamstrings stiffness may be important additions to ACL injury-prevention programs.

National athletic trainers' association position statement: skin diseases.

OBJECTIVE: To present recommendations for the prevention, education, and management of skin infections in athletes. BACKGROUND: Trauma, environmental factors, and infectious agents act together to continually attack the integrity of the skin. Close quarters combined with general poor hygiene practices make athletes particularly vulnerable to contracting skin diseases. An understanding of basic prophylactic measures, clinical features, and swift management of common skin diseases is essential for certified athletic trainers to aid in preventing the spread of infectious agents. RECOMMENDATIONS: These guidelines are intended to provide relevant information on skin infections and to give specific recommendations for certified athletic trainers and others participating in athletic health care.

Ankle bracing and the neuromuscular factors influencing joint stiffness.

CONTEXT: Health care professionals commonly prescribe external stabilization to decrease the incidence and severity of ankle sprains. The mechanism for this decrease is not clearly understood. Examining the effects of ankle bracing on biomechanical stability and influencing factors may provide important information regarding the neuromuscular effects of bracing. OBJECTIVE: To study the effects of 2 different ankle braces on the neuromuscular factors influencing ankle stiffness. DESIGN: Mixed-model repeated-measures design. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-eight physically active participants composing 2 groups: 14 with unilateral functional ankle instability (age = 26.19 +/- 6.46 years, height = 166.07 +/- 12.90 cm, mass = 69.90 +/- 13.46 kg) and 14 with bilaterally stable ankles (age = 23.76 +/- 5.82 years, height = 174.00 +/- 11.67 cm, mass = 68.60 +/- 13.12 kg). INTERVENTION(S): Participants were fitted with surface electromyography electrodes over the peroneus longus, peroneus brevis, tibialis anterior, and soleus muscles. Each participant received transient motion oscillations to his or her ankle on a custom-built medial-lateral swaying cradle in each of 3 conditions: no ankle brace (NB), lace-up brace (LU), and semirigid brace (SR). MAIN OUTCOME MEASURE(S): Ankle stiffness as measured by the cradle and preactivation levels (percentage of maximal voluntary isometric contraction) of the 4 test muscles. RESULTS: Stiffness levels increased across brace conditions (NB = 24.79 +/- 6.59 Nm/rad, LU = 28.29 +/- 7.05 Nm/rad, SR = 33.22 +/- 8.78 Nm/rad; F(2,52) = 66.185, P < .001). No differences were found between groups for rotational stiffness (stable = 27.36 +/- 6.17 Nm/rad, unstable = 30.18 +/- 8.21 Nm/rad; F(1,26) = 1.084, P = .307). Preactivation levels did not change for any of the tested muscles with the application of an ankle brace (F(2,52) = 1.326, P = .275). CONCLUSIONS: The increase in ankle rotational stiffness with the addition of an ankle brace and the lack of any demonstrable neuromuscular changes suggested ankle braces passively contributed to the stability of the system.

Effects of velocity-specific training on rate of velocity development, peak torque, and performance.

Little is known about the velocity-specific adaptations to training utilizing movement velocities in excess of 300 degrees x s(-1). The purpose of this investigation was to determine the effects of 4 weeks of slow (60 degrees x s(-1)) vs. fast (400 degrees x s(-1)) velocity training on rate of velocity development (RVD), peak torque (PT), and performance. Twenty male kinesiology students (22.0 years +/- 2.72; 178.6 cm +/- 7.1; 82.7 kg +/- 15.5) were tested, before and after 4 weeks of training, for PT production, RVD (at 60, 180, 300, 400, and 450 degrees x s(-1)), standing long jump (SLJ) distance, and 15- and 40-m sprint times. All participants underwent 8 training sessions, performing 5 sets of 5 repetitions of simultaneous, bilateral, concentric knee extension exercises on a Biodex System 3 isokinetic dynamometer at either 60 degrees or 400 degrees per second. Two 5 (speed) x 2 (time) x 2 (group) multivariate repeated measures analyses of variance revealed no significant differences between groups on any measure. Therefore, the groups were collapsed for analysis. There was a significant (p < 0.05) main effect for RVD by time and SLJ distance by time (pre- 227.1 cm +/- 21.2; post- 232.9 cm +/- 20.7) but no significant change in PT or 15- or 40-m sprint times. These results offer support for the suggestion that there is a significant neural adaptation to short-term isokinetic training performed by recreationally trained males, producing changes in limb acceleration and performance with little or no change in strength. Because results were independent of training velocity, it appears as though the intention to move quickly is sufficient stimulus to achieve improvements in limb RVD. Changes in SLJ distance suggest that open kinetic chain training may benefit the performance of a closed kinetic chain activity when movement pattern specificity is optimized.