Chris Connaboy

Intersession Reliability of Vertical Jump Height in Women and Men

Moir, G, Shastri, P, and Connaboy, C. Intersession reliability of vertical jump height in women and men. J Strength Cond Res 22(6): 1779-1784, 2008-The purpose of the present study was to investigate the intersession reliability of vertical jump height in women and men recorded from a contact mat. Thirty-five women and 35 men performed four testing sessions across a 4-week period, with each session separated by 1 week. Within each testing session, subjects completed three countermovement vertical jumps (CMJs) for maximum height. Reliability statistics were calculated using the highest jump (HIGH) and also from the mean of all three jumps (3 MEAN) during each session. Reliability was calculated as a change in the mean, coefficients of variation (CVs), and intraclass correlations coefficients (ICCs) between testing sessions. For women, jump heights were not substantially different between sessions for either the HIGH or 3 MEAN data. The CVs for women ranged from 4.4 to 6.6% for HIGH and 4.1 to 6.0% for 3 MEAN, with the corresponding ICCs ranging from 0.87 to 0.94 for HIGH and 0.90 to 0.95 for 3 MEAN. For men, jump heights were not substantially different between sessions for HIGH. However, jump heights during session 1 were substantially greater than those during session 2 when using the 3 MEAN data. CVs between sessions for HIGH ranged from 4.0 to 5.6%, and those for 3 MEAN ranged from 4.2 to 5.2%. The ICCs ranged from 0.87 to 0.93 for HIGH and from 0.89 to 0.93 for 3 MEAN. Given the maximal nature of vertical jump tests, it seems appropriate to use the highest jump from a number of trials for women and men when using a contact mat. Practitioners and researchers can use the data to identify the range in which the true value of an athletes score lies and calculate sample sizes for studies assessing height during CMJs recorded from a contact mat.

Measures of Reliability in the Kinematics of Maximal Undulatory Underwater Swimming

PURPOSE The purposes of this article were to establish the reliability of the kinematics of maximal undulatory underwater swimming (UUS) in skilled swimmers, to determine any requirement for familiarization trials, to establish the within-subject (WS) variability of the kinematics, and to calculate the number of cycles required to accurately represent UUS performance. METHODS Fifteen male swimmers performed 20 maximal UUS trials (two cycles per trial) during four sessions. The magnitude of any systematic bias present within the kinematic variables was calculated between session, trial, and cycle. Random error calculations were calculated to determine the WS variation. An iterative intraclass correlation coefficient (ICC) process was used to determine the number of cycles required to achieve a stable representation of each kinematic variable. RESULTS Significant differences were found between session 1 and all other sessions for several variables, indicating the requirement for a familiarization session. Results indicated a wide range of WS variation (coefficient of variation [CV] = 1.21%-12.42%). Reductions in WS variation were observed for all variables when the number of cycles of data used to calculate WS variation was increased. Using six cycles of data, including additional cycles of data, provided diminishing returns regarding the reduction of WS variation. The ICC analysis indicated that an average of nine cycles (mean ± SD = 9.47 ± 5.63) was required to achieve the maximum ICC values attained, and an average of four cycles (mean ± SD = 3.57 ± 2.09) was required to achieve an ICC of 0.95. CONCLUSIONS After determining the systematic bias and establishing the requirement for a familiarization session, six cycles of data were found to be sufficient to provide high levels of reliability (CV(TE) = 0.86-8.92; ICC = 0.811-0.996) for each of the UUS kinematic variables.

Three-dimensional analysis of intracycle velocity fluctuations in frontcrawl swimming

The purpose of this study was to determine accurately the magnitude and changes of intra‐cycle velocity fluctuation (Vfluc), maximum (Vmax) and minimum velocity (Vmin) of the center of mass during a maximum 200 m frontcrawl swim, and to examine whether they are associated with performance. Performance was indicated by the mean velocity (Vmean) of the stroke cycle (SC) in the swimming direction. The relative Vfluc, Vmax and Vmin were also calculated as a percentage of Vmean, while Vfluc was calculated for all three directions. Eleven male swimmers of national/international level participated in this study and their performance was recorded with four below‐ and two above‐water‐synchronized cameras. Four SCs were analyzed for the 200 m swim (one for each 50 m). Anthropometric data were calculated by the elliptical zone method. Vmean generally decreased throughout the test. Vmax and Vmin were positively correlated to performance and were significantly higher in SC1 than in the other SCs. However, the relative Vmax and Vmin values were remarkably consistent during the 200 m and not associated with performance. Despite the noteworthy magnitude of Vfluc in all directions, they were in general not correlated with performance and there were no significant changes during the test.

The key kinematic determinants of undulatory underwater swimming at maximal velocity

ABSTRACT The optimisation of undulatory underwater swimming is highly important in competitive swimming performance. Nineteen kinematic variables were identified from previous research undertaken to assess undulatory underwater swimming performance. The purpose of the present study was to determine which kinematic variables were key to the production of maximal undulatory underwater swimming velocity. Kinematic data at maximal undulatory underwater swimming velocity were collected from 17 skilled swimmers. A series of separate backward-elimination analysis of covariance models was produced with cycle frequency and cycle length as dependent variables (DVs) and participant as a fixed factor, as including cycle frequency and cycle length would explain 100% of the maximal swimming velocity variance. The covariates identified in the cycle-frequency and cycle-length models were used to form the saturated model for maximal swimming velocity. The final parsimonious model identified three covariates (maximal knee joint angular velocity, maximal ankle angular velocity and knee range of movement) as determinants of the variance in maximal swimming velocity (adjusted-r2 = 0.929). However, when participant was removed as a fixed factor there was a large reduction in explained variance (adjusted r2 = 0.397) and only maximal knee joint angular velocity continued to contribute significantly, highlighting its importance to the production of maximal swimming velocity. The reduction in explained variance suggests an emphasis on inter-individual differences in undulatory underwater swimming technique and/or anthropometry. Future research should examine the efficacy of other anthropometric, kinematic and coordination variables to better understand the production of maximal swimming velocity and consider the importance of individual undulatory underwater swimming techniques when interpreting the data.

Reliability of 1RM Split-Squat Performance and the Efficacy of Assessing Both Bilateral Squat and Split-Squat 1RM in a Single Session for Non-Resistance-Trained Recreationally Active Men.

Abstract Urquhart, BG, Moir, GL, Graham, SM, and Connaboy, C. Reliability of 1RM split-squat performance and the efficacy of assessing both bilateral squat and split-squat 1RM in a single session for non–resistance-trained recreationally active men. J Strength Cond Res 29(7): 1991–1998, 2015—The purpose of this study was to determine the reliability of 1 repetition maximum (1RM) split squat (SS) and establish the efficacy of collecting 1RM-SS and 1RM bilateral squat (BLS) data in the same session, for a non–resistance-trained recreationally active population. Fourteen males performed a submaximal familiarization session and 5 testing sessions. After familiarization, the 1RM-SS was tested in the following 3 sessions. In session 4, subjects were tested in both 1RM-SS and 1RM-BLS, with half performing SS then BLS and the remainder BLS then SS. In session 5, the testing order was reversed. Reliability statistics calculated included the following: changes in mean across sessions, coefficient of variation calculated from the typical error (TE) scores (%CVTE), and test-retest reliability (intraclass correlation coefficient [ICC]) of 1RM-SS. Statistically significant differences between the mean 1RM-SS in sessions 1 and 2 (2.14 kg, p = 0.001), and sessions 1 and 3 (2.86 kg, p < 0.003) were found, indicating the requirement for an additional familiarization session before 1RM-SS data collection. The %CVTE was 2.53% and the ICC was 0.97 for the 1RM-SS protocol. Performing SS before BLS tended to increase the mean 1RM-BLS (+2.1%), although the difference was not significant (p = 0.055). A reliable measure of 1RM-SS can be determined after 1 submaximal and 1 maximal familiarization session in non–resistance-trained recreationally active men. Analysis of the current data suggests that it is appropriate to perform both 1RM-SS and 1RM-BLS tests within the same testing session if 1RM-SS is performed before 1RM-BLS. However, further testing is warranted to firmly establish the effects of 1RM-SS on subsequent 1RM-BLS.

Prevention of exertional lower body musculoskeletal injury in tactical populations: protocol for a systematic review and planned meta-analysis of prospective studies from 1955 to 2018

BackgroundExertional lower body musculoskeletal injuries (ELBI) cost billions of dollars and compromise the readiness and job performance of military service and public safety workers (i.e., tactical populations). The prevalence and burden of such injuries underscores the importance of prevention efforts during activities necessary to sustain core occupational competencies. Attempts to synthesize prevention techniques specific to tactical populations have provided limited insight on the comparative efficacy of interventions that do not modify physical training practices. There is also a need to assess the influence of sex, exposure, injury classification scheme, and study design. Thus, the primary purpose of the systematic review and planned meta-analysis detailed in this protocol is to evaluate the comparative efficacy of ELBI prevention strategies in tactical populations.MethodsA systematic search strategy will be implemented in MEDLINE, EMBASE, Cochrane, and CINAHL. A multi-tiered process will be used to capture randomized controlled trials and prospective cohort studies that directly assess the prevention of ELBI in tactical population(s). Extracted data will be used to compare prevention strategies and assess the influence of heterogeneity related to occupation, sex, exposure, injury characteristics, and study quality. In addition, individual risk of bias, meta-bias, and the quality of the body of evidence will be rigorously tested.DiscussionThis systematic review and planned meta-analysis will comprehensively evaluate ELBI mitigation strategies in tactical populations, elucidate factors that influence responses to treatment, and assess the overall quality of the body of research. Results of this work will guide the prioritization of ELBI prevention strategies and direct future research efforts, with direct relevance to tactical, health and rehabilitation science, and human performance optimization stakeholders.Systematic review registrationThe systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 3 Jan 2018 (registration number CRD42018081799).

Using Drop Jumps and Jump Squats to Assess Eccentric and Concentric Force-Velocity Characteristics

The purpose of this study was to investigate the eccentric and concentric force-velocity (Fv) characteristics recorded during drop jumps (DJ) from different heights and loaded jump squats (JS) and to determine the number of jumps required to accurately model the eccentric and concentric Fv relationships. Fourteen resistance-trained men (age: 21.9 ± 1.8 years) performed a countermovement jump (CMJ) and DJ from heights of 0.40, 0.60, and 0.80 m. JS with loads equivalent to 0%, 27%, 56%, and 85% 1-repetition maximum were performed in a separate session. Force platforms and a 3-D motion analysis system were used to record the average force (F¯) and velocity (v¯) during the absorption (CMJ, DJ40, DJ60, DJ80) and propulsion (JS0, JS27, JS56, JS85) phases of the jumps. Eccentric (absorption phase) and concentric (propulsion phase) Fv characteristics were then calculated and linear regression equations were determined when the number of jumps included was varied. F¯ during the absorption phase significantly increased from CMJ to DJ60 while v¯ increased significantly from CMJ to DJ80. The two-point method (CMJ, DJ80) resulted in a significantly lower y-intercept (mean difference [MD]: 0.7 N/kg) and a greater slope (MD: 0.7 Ns/m) for the eccentric Fv characteristics compared to the multiple-point method. F¯ increased significantly and v¯ decreased significantly with increasing external load in the JS conditions. The two-point method (JS0, JS85) resulted in a significantly greater y-intercept (MD: 1.1 N/kg) compared to the multiple-point method for the concentric Fv characteristics. Both DJ and loaded JS may provide means of assessing the eccentric and concentric Fv characteristics with only two jumps being required.

Assessing Plyometric Ability during Vertical Jumps Performed by Adults and Adolescents

The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players (age: 16.5 ± 0.7 years) performed a CMJ and a DJ from a height of 0.40 m. Jump height (JH), contact time, normalized work (WNORM), and power output (PONORM) during the absorption and propulsion phases were calculated from force platforms and 3-D motion analysis data. Plyometric ability was assessed using the modified reactive strength index (RSIMOD during CMJ) and the reactive strength index (RSI during DJ) as well as three indices using propulsion time, propulsion work (PWI), and propulsion power. Adults jumped significantly higher than adolescents (mean difference [MD]: 0.05 m) while JH (MD: 0.05 m) and ground contact time (MD: 0.29 s) decreased significantly from CMJ to DJ. WNORM (MD: 4.2 J/kg) and PONORM (MD: 24.2 W/kg) during the absorption phase of CMJ were significantly less than these variables during the propulsion phases of the jumps. The reactive strength index variants increased significantly from the CMJ to DJ (MD: 0.23) while all other plyometric indices decreased significantly. Neither RSIMOD nor RSI contributed significantly to the prediction of JH during CMJ and DJ, respectively, while PWI was able to explain ≥68% of the variance in JH. Variants of the reactive strength index do not reflect the changes in mechanical variables during the ground contact phase of CMJ and DJ and may not provide an accurate assessment of plyometric ability during different vertical jumps.

Significantly Increased Odds of Reporting Previous Shoulder Injuries in Female Marines Based on Larger Magnitude Shoulder Rotator Bilateral Strength Differences

Background: Musculoskeletal injuries to the extremities are a primary concern for the United States (US) military. One possible injury risk factor in this population is side-to-side strength imbalance. Purpose: To examine the odds of reporting a previous shoulder injury in US Marine Corps Ground Combat Element Integrated Task Force volunteers based on side-to-side strength differences in isokinetic shoulder strength. Study Design: Cohort study; Level of evidence, 3. Methods: Male (n = 219) and female (n = 91) Marines were included in this analysis. Peak torque values from 5 shoulder internal/external rotation repetitions were averaged and normalized to body weight. The difference in side-to-side strength measurements was calculated as the absolute value of the limb difference divided by the mean peak torque of the dominant limb. Participants were placed into groups based on the magnitude of these differences: <10%, 10% to 20%, and >20%. Odds ratios (ORs) and 95% CIs were calculated. Results: When separated by sex, 13.2% of men reported an injury, while 5.5% of women reported an injury. Female Marines with >20% internal rotation side-to-side strength differences demonstrated increased odds of reporting a previous shoulder injury compared with female Marines with <10% strength differences (OR, 15.4; 95% CI, 1.4-167.2; P = .03 ) and female Marines with 10% to 20% strength differences (OR, 13.9; 95% CI, 1.3-151.2; P = .04). No significant ORs were demonstrated in male Marines. Conclusion: Marines with larger magnitude internal rotation strength differences demonstrated increased odds of reporting a previous shoulder injury compared with those with lesser magnitude differences. Additionally, female sex appears to drastically affect the increased odds of reporting shoulder injuries (OR, 13.9-15.4) with larger magnitude differences (ie, >20%) compared with those with lesser magnitude differences (ie, <10% and 10%-20%). The retrospective cohort design of this study cannot delineate cause and effect but establishes a relationship between female Marines and greater odds of larger magnitude strength differences after returning from an injury.

The effects of British Army footwear on ground reaction force and temporal parameters of British Army foot-drill

High rates of occupational training-related lower-limb musculoskeletal [MSK] overuse injuries are reported for British Army recruits during basic training. Foot-drill is a repetitive impact loading occupational activity and involves striking the ground violently with an extended-knee [straight-leg] landing. Foot-drill produces vertical ground reaction forces [vGRF] equal to and/or greater than those reported for high-level plyometric exercises/activities. Shock absorbing footwear aid in the attenuation of the magnitude of vGRF, resulting in a reduced risk of lower-limb MSK overuse injury when running. The potential shock absorbing characteristics of standard issue British Army footwear on the magnitude of vGRF and temporal parameters of foot-drill are scant. Therefore, this study sought to determine the magnitude of, and examine changes in vGRF and temporal parameters of foot-drill across three types of British Army footwear. Sampled at 1000hz, the mean of eight-trials from fifteen recreationally active males were collected from four foot-drills; stand-at-ease [SaE], stand-at-attention [SaA], quick-march [QM] and halt. Analysis of a normal walk was included to act as a comparison with quick-march. Significant main effects [P<0.05] were observed between footwear and foot-drill. The training shoe demonstrated significantly greater shock absorbing capabilities when compared with the combat boot and ammunition boot. Foot-drill produced peak vGRF and peak vertical rate of force development in excess of 5bw, and 350bw/sec, respectively. Time to peak vGRF ranged from 0.016- 0.036ms across foot-drills, indicating that passive vGRF may not be under neuromuscular control. The marginal reductions in the magnitude of vGRF and temporal parameters in foot-drill associated with the training shoe may act to reduce the accumulative impact loading forces experienced by recruits, subsequently minimising the severity and rates of lower-limb MSK overuse injuries and recruit medical discharges during basic training.