Gavin L. Moir

Influence Of Familiarization On The Reliability Of Vertical Jump And Acceleration Sprinting Performance In Physically Active Men

The purpose of the present study was to determine the number of familiarization sessions required to obtain an accurate measure of reliability associated with loaded vertical jump and 20-m sprint running performance. Ten physically active men attended 5 separate testing sessions over a 3-week period where they performed unloaded and loaded (10-kg extra load) countermovement (CMJ) and static (SJ) jumps, followed by straight-line 20-m sprints. Jump height was recorded for the vertical jumps using a jump mat, while the time for 10 m and 20 m was recorded during the sprints using photocells. The highest (jump conditions) and fastest (sprint) of 3 trials performed during each of the 5 testing sessions was used in the subsequent analysis. Familiarization was assessed using the scores obtained during the 5 separate testing sessions. Reliability was assessed by calculating intra-class correlation coefficients (ICCs) and coefficient of variation (CV). No significant differences were obtained between the testing sessions for any of the measures. ICCs ranged from 0.89 to 0.95, while CVs ranged from 1.9 to 2.6%. These results indicate that high levels of reliability can be achieved without the need for familiarization sessions when using loaded and unloaded CMJ and SJ and 20-m sprint performance with physically active men.

Three Different Methods of Calculating Vertical Jump Height from Force Platform Data in Men and Women

The purpose of the present study was to investigate the effects of different methods to calculate vertical jump height in men and women. Fifty men and 50 women performed three countermovement vertical jumps for maximal height on a force platform, the highest of which was used in the statistical analyses. The peak displacement attained by the center of mass (COM) during flight was obtained from three different calculations: (1) using the time in the air (TIA), (2) using the vertical velocity of the COM at take-off (TOV), and (3) adding the positive vertical displacement of the COM prior to take-off to the height calculated using TOV (TOV+s). With all calculations, men produced significantly greater jump heights than women (p < 0.05). TIA produced significantly greater jump heights than TOV in men and women, while TOV+s produced significantly greater jump heights than both TIA and TOV in men and women (p < 0.05). Despite these differences, the methods produced consistent results for both men and women. All calculation methods have logical validity, depending upon the definition of jump height used. Therefore, the method used to calculate jump height should be determined by the equipment available to the practitioner while giving consideration to the sources of error inherent in each method. Based upon the present findings, when using a force platform to calculate vertical jump height, practitioners are encouraged to use the TOV method.

The acute effects of heavy back and front squats on speed during forty-meter sprint trials

The purpose of the present study was to investigate the effects of performing heavy back squats (HBS) and heavy front squats (HFS) on the average speed during each 10-m interval of 40-m sprint trials. In a randomized, cross-over design, 10 strength-trained men performed a HBS, HFS, or control treatment before performing three 40-m sprint trials separated by 3 minutes. The HBS and HFS treatments consisted of performing parallel back or front squats with 30%, 50%, and 70% of the subjects 1 repetition maximum after 5 minutes of cycling. The control treatment consisted of cycling for 5 minutes. The sprint trials were performed 4 minutes after completing the HBS, HFS, or control treatments. Significant increases in speed were found during the 10- to 20-m interval for the HBS compared with the control treatment (mean difference, 0.12 m·s−1; 95% likely range, 0.05-0.18 m·s−1; P = 0.001). During the 30- to 40-m interval, HBS produced significantly greater speeds compared with the HFS treatment (mean difference, 0.24 m·s−1; 95% likely range, 0.02-0.45 m·s−1; P = 0.034) and the control treatment (mean difference, 0.18 m·s−1; 95% likely range, 0.03-0.32 m·s−1; P = 0.021). The differing effects of the treatments may reflect different levels of muscular activation or different mechanical aspects of the squat exercises. Similarly, the multidimensional nature of sprint running means that other specific exercises may confer improvements in sprinting performance during other intervals. It is suggested that coaches could incorporate HBS into the warm-up procedure of athletes to improve sprinting performance.

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.

The influence of familiarization on the reliability of force variables measured during unloaded and loaded vertical jumps.

The purpose of this study was to determine the number of familiarization sessions required to obtain an accurate measure of reliability associated with force variables recorded during unloaded and loaded (30 and 60% of 1 repetition maximum squat [1RM]) static vertical jumps (SJ). Nine physically active men attended 4 separate testing sessions over a 2-week period. Force platform recordings of peak force, peak rate of force development (pRFD), average rate of force development, takeoff velocity, average power, and peak power were obtained for each jump. During each of the 4 testing sessions, 3 jumps were performed under each of the load conditions. The average of the force variables were used in the analysis. Familiarization was assessed using the scores obtained during the 4 separate testing sessions. Reliability was assessed by calculating intraclass correlation coefficients (ICCs) and coefficient of variation (CV) associated with the force variables. No significant differences (p > 0.05) were obtained between the testing sessions for any of the force variables. With the exception of pRFD, the force variables showed reasonably good levels of test-retest reliability (ICC range: 0.75–0.99; CV range: 1.2–7.6%). High levels of reliability can be achieved in a variety of force variables without the need for familiarization sessions when performing SJ under unloaded conditions and with loads of 30 and 60% of 1RM squat with physically active men.

Effect of static and dynamic stretching on vertical jump performance in collegiate women volleyball players.

Dalrymple, KJ, Davis, SE, Dwyer GB, and Moir, GL. Effect of static and dynamic stretching on vertical jump performance in collegiate women volleyball players. J Strength Cond Res 24(1): 149-155, 2010-The purpose of this study was to determine the effect of stretching on peak jump height during a series of vertical jumps, specifically focusing on a) static stretching (SS), b) dynamic stretching (DS) and c) no stretching (NS) performed immediately before a series of countermovement vertical jumps (CMJ). Twelve female collegiate volleyball players (mean ± SD; age 19.5 ± 1.1 yr; height 1.71 ± 0.06 m; mass 71.3 ± 8.54 kg) volunteered for this study. Data collection lasted a total of 3 weeks, and each subject performed all 3 stretching protocols, 1 session per week, with 1 week between sessions. The order of the stretching protocols was randomized for each subject. During each testing session, all subjects performed a 5-minute light jog as a warm-up, followed by 8 minutes of 1 of the stretching protocols. One minute after the completion of each protocol, 5 maximal CMJ were performed on a force platform, with each jump separated by 1 minute of passive recovery. Jump heights were calculated by integrating the vertical force trace. There were no significant differences between the SS, DS, and NS conditions for any of the jumps (p > 0.05). Despite the lack of significant effects for the group, there were notable individual responses to each of the warm-up conditions. Practitioners should be aware of the individual responses of their athletes to different types of warm-up protocols before athletic performance and the possible impact of prescribing or eliminating certain exercises.

The Influence of Recovery Duration on Multiple Sprint Cycling Performance

The purpose of this study was to examine the influence of recovery duration on various measures of multiple sprint cycling performance. Twenty-five physically active men completed 2 maximal multiple sprint (20 x 5 seconds) cycling tests with contrasting recovery periods (10 or 30 seconds). The mean +/- SD values for age, height, and body mass were 20.6 +/- 1.5 years, 177.2 +/- 5.4 cm, and 78.2 +/- 8.2 kg, respectively. All tests were conducted on a friction-braked cycle ergometer. Longer (30 seconds) recovery periods resulted in significantly (p < 0.05) higher measures of maximum (approximately 4%) and mean (approximately 26%) power output, the former appearing to result from a potentiation effect during the first few sprints. Thirty-second recovery periods also corresponded with significantly lower measures of fatigue (absolute difference: 16.1%; 95% likely range: 14.1-18.2%), heart rate, respiratory exchange ratio, and oxygen uptake. Blood lactate and ratings of perceived exertion (6-20 scale) increased progressively throughout both protocols and were significantly lower with 30-second recovery periods. The results of this study illustrate the considerable influence of recovery duration on various measures of multiple sprint work. Although the precise mechanisms of this response require further investigation, coaches and sport scientists should consider these findings when attempting to develop or evaluate the performance capabilities of athletes involved in multiple sprint sports.

the Reliability and Validity of Fatigue Measures During Short-duration Maximal-intensity Intermittent Cycling

&NA; Glaister, M., M.H. Stone, A.M. Stewart, M. Hughes, and G.L. Moir. The reliability and validity of fatigue measures during short‐duration maximal‐intensity intermittent cycling. J. Strength Cond. Res. 18(3):459–462. 2004.—The purpose of the present study was to assess the reliability and validity of fatigue measures, as derived from 4 separate formulae, during tests of repeat sprint ability. On separate days over a 3‐week period, 2 groups of 7 recreationally active men completed 6 trials of 1 of 2 maximal (20 × 5 seconds) intermittent cycling tests with contrasting recovery periods (10 or 30 seconds). All trials were conducted on a friction‐braked cycle ergometer, and fatigue scores were derived from measures of mean power output for each sprint. Apart from formula 1, which calculated fatigue from the percentage difference in mean power output between the first and last sprint, all remaining formulae produced fatigue scores that showed a reasonably good level of test‐retest reliability in both intermittent test protocols (intraclass correlation range: 0.78–0.86; 95% likely range of true values: 0.54–0.97). Although between‐protocol differences in the magnitude of the fatigue scores suggested good construct validity, within‐protocol differences highlighted limitations with each formula. Overall, the results support the use of the percentage decrement score as the most valid and reliable measure of fatigue during brief maximal intermittent work.

An Investigation Into the Relationship of Flexibility, Power, and Strength to Club Head Speed in Male Golfers

Gordon, BS, Moir, GL, Davis, SE, Witmer, CA, and Cummings, DM. An investigation into the relationship of flexibility, power, and strength to club head speed in male golfers. J Strength Cond Res 23(5): 1606-1610, 2009-The purpose of this study was to investigate the relationship of flexibility, power, and strength to club head speed (CHS) in male golfers. Fifteen golfers (mean age ± SD: 34.3 ± 13.6 years) with a handicap of ≤8 volunteered for the study. Following a standardized warm-up, subjects proceeded to hit 5 wiffle golf balls with a 5 iron while their CHS was measured. Rotational trunk flexibility was measured on a trunk rotator machine. An index of total body rotational power was measured through a hip toss with a 3-kg medicine ball while an 8-repetition maximum (RM) on a pec deck machine was used to measure chest strength. Pearson correlations were used to assess the magnitude of the relationships between CHS and the measures of flexibility, power, and strength. Partial correlations were then run to assess the effect of handicap on the observed relationships. The only variables that were significantly correlated to CHS were chest strength (r = 0.69, p < 0.05) and total body rotational power (r = 0.54, p < 0.05). These relationships were unchanged when the effect of handicap was controlled for. The results of this study show that strength of the chest in the pec deck motion and total body rotational power significantly correlate with CHS in male golfers. This information can be used by practitioners to develop training programs and field tests for golfers.

The Influence of Endurance Training on Multiple Sprint Cycling Performance

The aims of the present study were to examine the effects of endurance training on multiple sprint cycling performance and to evaluate the influence of recovery duration on the magnitude of those effects. Twenty-one physically active male university students were randomly assigned to either an experimental (n = 12) or a control (n = 9) group. The experimental group cycled for 20 minutes each day, 3 times per week, for 6 weeks at 70% of the power output required to elicit maximal oxygen uptake ([latin capital V with dot above]O2max). Multiple sprint performance was assessed using 2 maximal (20 X 5 seconds) sprint cycling tests with contrasting recovery periods (10 or 30 seconds). All tests were conducted on a friction-braked cycle ergometer. Relative to controls, training resulted in a 0.2 L[middle dot]min-1 increase in mean [latin capital V with dot above]O2max (95% likely range: -0.04 to 0.44 L[middle dot]min-1). Changes in anaerobic capacity (determined by maximal accumulated oxygen deficit) over the same period were trivial (p = 0.96). After training, the experimental group showed significant improvements (~40 W), relative to controls, in multiple sprint measures of peak and mean power output. In contrast, training-induced reductions in fatigue were trivial (p = 0.63), and there were no significant between-protocol differences in the magnitude of any effects. In summary, 6 weeks of endurance training resulted in substantial improvements in multiple sprint cycling performance, the magnitude of the improvements being largely unaffected by the duration of the intervening recovery periods.