The force-production characteristics of 3 weight-lifting derivatives were examined by comparing the force-time curves of each exercise. Sixteen resistance-trained men performed repetitions of the hang power clean (HPC), jump shrug (JS), and hang high pull (HHP) on a force platform at several relative loads. Relative peak force (PF), relative impulse (IMP), peak rate of force development (PRFD), and time-normalized force-time curves of each exercise were compared. The JS produced greater PF than the HPC (P < .001, d = 1.38) and HHP (P < .001, d = 1.14), while there was no difference between the HPC and HHP (P = .338, d = 0.26). Similarly, the JS produced greater IMP than the HPC (P < .001, d = 0.52) and HHP (P = .019, d = 0.36). The HHP also produced greater IMP than the HPC (P = .040, d = 0.18). Finally, the JS produced greater PRFD than the HPC (P < .001, d = 0.73) and HHP (P = .001, d = 0.47), while there was no difference between the HPC and HHP (P = .192, d = 0.22). The HPC, JS, and HHP force-time profiles were similar during the first 75-80% of the movement; however, the JS produced markedly different force-time characteristics in the final 20-25% of the movement. The JS produced superior force-production characteristics, namely PF, IMP, and PRFD, as well as a unique force-time profile, compared with the HPC and HHP across several loads.

The purposes of this study included examining the reliability of reactive strength index-modified (RSImod), the relationships between RSImod and force-time variables, and the differences in RSImod between male and female collegiate athletes. One hundred six Division I collegiate athletes performed unloaded and loaded countermovement jumps (CMJs). Intraclass correlation coefficients and typical error expressed as a coefficient of variation were used to establish the relative and absolute reliability of RSImod, respectively. Pearson zero-order product-moment correlation coefficients were used to examine the relationships between RSImod and rate of force development, peak force (PF), and peak power (PP) during unloaded and loaded jumping conditions. Finally, independent samples t-tests were used to examine the sex differences in RSImod between male and female athletes. Intraclass correlation coefficient values for RSImod ranged from 0.96 to 0.98, and typical error values ranged from 7.5 to 9.3% during all jumping conditions. Statistically significant correlations existed between RSImod and all force-time variables examined for male and female athletes during both jumping conditions (p ≤ 0.05). Statistically significant differences in RSImod existed between male and female athletes during both unloaded and loaded CMJs (p < 0.001). Reactive strength index-modified seems to be a reliable performance measurement in male and female athletes. Reactive strength index-modified may be described and used as a measure of explosiveness. Stronger relationships between RSImod, PF, and PP existed in female athletes as compared with that in male athletes; however, further evidence investigating these relationships is needed before conclusive statements can be made. Male athletes produced greater RSImod values as compared with that produced by female athletes.

Sole, CJ, Mizuguchi, S, Sato, K, Moir, GL, and Stone, MH. Phase characteristics of the countermovement jump force-time curve: a comparison of athletes by jumping ability. J Strength Cond Res 32(4): 1155-1165, 2018-The purpose of this study was to compare the phase characteristics of the countermovement jump (CMJ) force-time (F-t) curve between athletes based on jumping ability. An initial sample of one-hundred fifty Division-I collegiate athletes were ranked based on CMJ height. Three performance groups were then formed by taking the top, middle, and lower 30 athletes (15 men and 15 women) from the sample. Phases of the CMJ F-t curve were determined and then characterized by their duration, magnitude, area (impulse), and shape (shape factor). A series of 3-way mixed analysis of variance were used to determine statistical differences in phase characteristics between performance groups as well as between male and female athletes. Statistically significant phase-by-performance group interactions were observed for relative phase magnitude (p < 0.001), relative phase impulse (p < 0.001), and shape factor (p = 0.002). Phase-by-sex interactions were statistically significant for both relative phase magnitude (p < 0.001) and relative phase impulse (p < 0.001). Post hoc comparisons indicated that higher jumpers exhibited larger relative magnitude and impulse in the phases contained within the positive area of the F-t curve. Similarly, relative phase magnitude and impulse were the only phase characteristics to be statically different between men and women. Finally, the relative shape of the phase representing the initial rise in force was found to relate to jump height. These results provide some information regarding the diagnostic value of qualitative analysis of the CMJ F-t curve.

The purpose of this study was to examine the differences in reactive strength index-modified (RSImod), jump height (JH), and time to takeoff (TTT) between 6 U.S. collegiate sport teams. One hundred six male and female Division I collegiate athletes performed unloaded (<1 kg) and loaded (20 kg) countermovement jumps as part of an ongoing athlete monitoring program. Reactive strength index-modified, JH, and TTT values for each team were compared using 1-way analysis of variance. Statistically significant differences in RSImod (p < 0.001), JH (p < 0.001), and TTT (p = 0.003) existed between teams during the unloaded jumping condition. Similarly, statistically significant differences in RSImod (p < 0.001), JH (p < 0.001), and TTT (p = 0.028) existed between teams during the loaded jumping condition. Men's soccer and baseball produced the greatest RSImod values during both the unloaded and loaded jumping conditions followed by women's volleyball, men's tennis, women's soccer, and women's tennis. The greatest JH during unloaded and loaded jumping conditions was produced by men's baseball followed by men's soccer, women's volleyball, men's tennis, women's soccer, and women's tennis. Men's soccer produced shorter TTT compared with men's baseball (12.7%) and women's soccer (13.3%) during the unloaded and loaded jumping conditions, respectively. Collegiate sport teams exhibit varying reactive strength characteristics during unloaded and loaded jumping conditions. Understanding the differences in RSImod between sports may help direct the creation of training and monitoring programs more effectively for various sports.

The purpose of this study was to compare 4 methods that assess the lower-body stretch-shortening cycle (SSC) utilization of athletes. Eighty-six National Collegiate Athletic Association Division I athletes from 6 different sports performed 2 squat jumps and 2 countermovement jumps on a force platform. Pre-stretch augmentation percentage (PSAP), eccentric utilization ratio (EUR), and reactive strength (RS) for jump height (JH) and peak power (PP) magnitudes, and reactive strength index-modified (RSImod) were calculated for each team. A series of one-way analyses of variance with a Holm-Bonferroni sequential adjustment were used to compare differences in PSAP, EUR, RS, and RSImod between teams. Statistical differences in RSImod (p < 0.001) existed between teams, whereas no statistical differences in PSAP-JH (p = 0.150), PSAP-PP (p = 0.200), EUR-JH (p = 0.150), EUR-PP (p = 0.200), RS-JH (p = 0.031), or RS-PP (p = 0.381) were present. The relationships between PSAP, EUR, and RS measures were all statistically significant and ranged from strong to nearly perfect (r = 0.569-1.000), while most of the relationships between PSAP, EUR, and RS measures and RSImod were trivial to small (r = 0.192-0.282). Pre-stretch augmentation percentage and EUR, RS, and RSImod values indicate that women's tennis, men's soccer, and men's soccer teams may use the SSC most effectively, respectively. Pre-stretch augmentation percentage, EUR, RS, and RSImod values may show vastly different results when comparing an individual's and a team's ability to use the SSC. Practitioners should consider using RSImod to monitor the SSC utilization of athletes due to its timing component.

The purpose of this study was to determine the acute effects of heavy resistance exercise on agility performance in court-sport athletes. Five men (age: 20.6 ± 1.9 years; body mass: 79.36 ± 11.74 kg; body height: 1.93 ± 0.09 m) and five women (age 21.2 ± 2.7 years; body mass: 65.8 ± 10.18 kg; body height 1.77 ± 0.08 m) volunteered to participate in the present study. All subjects were NCAA Division II athletes who currently participated in tennis or basketball and all had previous resistance training experience of at least one year. In a counterbalanced design, agility performance during a 10 m shuttle test was assessed following either a dynamic warm-up (DW) or heavy resistance warm-up (HRW) protocol. The HRW protocol consisted of three sets of squats at 50, 60, and 90% of 1-RM. Agility performance was captured using an eight camera motion analysis system and the mechanical variables of stride length, stride frequency, stance time, flight time, average ground reaction force, as well as agility time were recorded. No significant differences were reported for the HRW and DW protocols for any of the mechanical variables (p>0.05), although there was a trend towards the HRW protocol producing faster agility times compared to the control protocol (p = 0.074). Based on the trend towards a significant effect, as well as individual results it is possible that HRW protocols could be used as an acute method to improve agility performance in some court-sport athletes.

A four-year retrospective analysis of injury data was conducted on a collegiate (NCAA Division I) women’s volleyball team. Twenty athletes (Year 1: age = 19.4 ± 0.9 y, height = 175.2 ± 5.1 cm, body mass = 70.5 ± 10.2 kg; Year 2: age = 20.1 ± 1.0 y, height = 175.7 ± 4.7 cm, body mass = 69.5 ± 10.1 kg; Year 3: age = 20.1 ± 1.4 y, height = 173.8 ± 6.3 cm, body mass = 69.9 ± 10.8 kg; Year 4: age = 19.5 ± 1.4 y, height = 174.4 ± 8.6 cm, body mass = 72.7 ± 10.8 kg) participated in this study, accounting for 1483 total training exposures. Injury was defined as any damage to a body part, incurred during volleyball or strength and conditioning-related activities, which interfered with training and/or competition. Injury rate was normalized to the number of athletes and exposure and expressed as injuries per 1000 exposures. A total of 133 injuries were recorded. The most common injury was to the knee (left = 7.5%, right = 12.0%). Injuries occurred most often in volleyball practice (75.2%), followed by competition (20.3%), and strength and conditioning-related activities (4.5%). Non-contact injuries (upper body = 26.3%, lower body = 53.4%) were more common than contact injuries (upper-body = 13.5%, lower-body = 6.8%). An examination of injury rates relative to the training year revealed patterns in injury occurrence. Specifically, spikes in injury rate were consistently observed during periods of increased training volume that were preceded by breaks in organized training, such as the early pre-season and off-season training periods.

Spinal cord injury (SCI) affects approximately 300,000 people in the United States. Most individuals who sustain severe SCI also develop subsequent osteoporosis. However, beyond immobilization-related lack of long bone loading, multiple mechanisms of SCI-related bone density loss are incompletely understood. Recent findings suggest neuronal impairment and disability may lead to an upregulation of receptor activator of nuclear factor-κB ligand (RANKL), which promotes bone resorption. Disruption of Wnt signaling and dysregulation of RANKL may also contribute to the pathogenesis of SCI-related osteoporosis. Estrogenic effects may protect bones from resorption by decreasing the upregulation of RANKL. This review will discuss the current proposed physiological and cellular mechanisms explaining osteoporosis associated with SCI. In addition, we will discuss emerging pharmacological and physiological treatment strategies, including the promising effects of estrogen on cellular protection.