Keir T. Hansen

STRENGTH AND POWER PREDICTORS OF SPORTS SPEED

For many sporting activities, initial speed rather than maximal speed would be considered of greater importance to successful performance. The purpose of this study was to identify the relationship between strength and power and measures of first-step quickness (5-m time), acceleration (10-m time), and maximal speed (30-m time). The maximal strength (3 repetition maximum [3RM]), power (30-kg jump squat, countermovement, and drop jumps), isokinetic strength measures (hamstring and quadriceps peak torques and ratios at 608·s-1 and 3008·s-1) and 5-m, 10-m, and 30-m sprint times of 26 part-time and full-time professional rugby league players (age 23.2 ± 3.3 years) were measured. To examine the importance of the strength and power measures on sprint performance, a correlational approach and a comparison between means of the fastest and slowest players was used. The correlations between the 3RM, drop jump, isokinetic strength measures, and the 3 measures of sport speed were nonsignificant. Correlations between the jump squat (height and relative power output) and countermovement jump height and the 3 speed measures were significant (r = −0.43 to −0.66, p < 0.05). The squat and countermovement jump heights as well as squat jump relative power output were the only variables found to be significantly greater in the fast players. It was suggested that improving the power to weight ratio as well as plyometric training involving countermovement and loaded jump-squat training may be more effective for enhancing sport speed in elite players.

Relationship between sprint times and the strength/power outputs of a machine squat jump.

Strength testing is often used with team-sport athletes, but some measures of strength may have limited prognostic/diagnostic value in terms of the physical demands of the sport. The purpose of this study was to investigate relationships between sprint ability and the kinetic and kinematic outputs of a machine squat jump. Thirty elite level rugby union and league athletes with an extensive resistance-training background performed bilateral concentric-only machine squat jumps across loads of 20% to 90% 1 repetition maximum (1RM), and sprints over 10 meters and 30 or 40 meters. The magnitudes of the relationships were interpreted using Pearson correlation coefficients, which had uncertainty (90% confidence limits) of ∼±0.3. Correlations of 10-meter sprint time with kinetic and kinematic variables (force, velocity, power, and impulse) were generally positive and of moderate to strong magnitude (r = 0.32-0.53). The only negative correlations observed were for work, although the magnitude was small (r = −0.18 to −0.26). The correlations for 30- or 40-meter sprint times were similar to those for 10-meter times, although the correlation with work was positive and moderate (r = 0.35-0.40). Correlations of 10-meter time with kinetic variables expressed relative to body mass were generally positive and of trivial to small magnitude (r = 0.01-0.29), with the exceptions of work (r = −0.31 to −0.34), and impulse (r = −0.34 to −0.39). Similar correlations were observed for 30- and 40-meter times with kinetic measures expressed relative to body mass. Although correlations do not imply cause and effect, the preoccupation with maximizing power output in this particular resistance exercise to improve sprint ability appears problematic. Work and impulse are potentially important strength qualities to develop in the pursuit of improved sprinting performance.

Squat jump training at maximal power loads vs. heavy loads: effect on sprint ability.

Harris, NK, Cronin, JB, Hopkins, WG, and Hansen, KT. Squat jump training at maximal power loads vs. heavy loads: effect on sprint ability. J Strength Cond Res 22(6): 1742-1749, 2008-Training at a load maximizing power output (Pmax) is an intuitively appealing strategy for enhancement of performance that has received little research attention. In this study we identified each subjects Pmax for an isoinertial resistance training exercise used for testing and training, and then we related the changes in strength to changes in sprint performance. The subjects were 18 well-trained rugby league players randomized to two equal-volume training groups for a 7-week period of squat jump training with heavy loads (80% 1RM) or with individually determined Pmax loads (20.0-43.5% 1RM). Performance measures were 1RM strength, maximal power at 55% of pretraining 1RM, and sprint times for 10 and 30 m. Percent changes were standardized to make magnitude-based inferences. Relationships between changes in these variables were expressed as correlations. Sprint times for 10 m showed improvements in the 80% 1RM group (−2.9 ± 3.2%) and Pmax group (−1.3 ± 2.2%), and there were similar improvements in 30-m sprint time (−1.9 ± 2.8 and −1.2 ± 2.0%, respectively). Differences in the improvements in sprint time between groups were unclear, but improvement in 1RM strength in the 80% 1RM group (15 ± 9%) was possibly substantially greater than in the Pmax group (11 ± 8%). Small-moderate negative correlations between change in 1RM and change in sprint time (r ≈ −0.30) in the combined groups provided the only evidence of adaptive associations between strength and power outputs, and sprint performance. In conclusion, it seems that training at the load that maximizes individual peak power output for this exercise with a sample of professional team sport athletes was no more effective for improving sprint ability than training at heavy loads, and the changes in power output were not usefully related to changes in sprint ability.

Do force-time and power-time measures in a loaded jump squat differentiate between speed performance and playing level in elite and elite junior rugby union players?

Hansen, KT, Cronin, JB, Pickering, SL, and Douglas, L. Do force-time and power-time measures in a loaded jump squat differentiate between speed performance and playing level in elite and elite junior rugby union players? J Strength Cond Res 25(9): 2382-2391, 2011—The purpose of this study was to investigate the discriminative ability of rebound jump squat force-time and power-time measures in differentiating speed performance and competition level in elite and elite junior rugby union players. Forty professional rugby union players performed 3 rebound jump squats with an external load of 40 kg from which a number of force-time and power-time variables were acquired and analyzed. Additionally, players performed 3 sprints over 30 m with timing gates at 5, 10, and 30 m. Significant differences (p < 0.05) between the fastest 20 and slowest 20 athletes, and elite (n = 25) and elite junior (n = 15) players in speed and force-time and power-time variables were determined using independent sample t-tests. The fastest and slowest sprinters over 10 m differed in peak power (PP) expressed relative to body weight. Over 30 m, there were significant differences in peak velocity and relative PP and rate of power development. There was no significant difference in speed over any distance between elite and elite junior rugby union players; however, a number of force and power variables including peak force, PP, force at 100 milliseconds from minimum force, and force and impulse 200 milliseconds from minimum force were significantly (p < 0.05) different between playing levels. Although only power values expressed relative to body weight were able to differentiate speed performance, both absolute and relative force and power values differentiated playing levels in professional rugby union players. For speed development in rugby union players, training strategies should aim to optimize the athletes power to weight ratio, and lower body resistance training should focus on movement velocity. For player development to transition elite junior players to elite status, adding lean mass is likely to be most beneficial.

Does cluster loading enhance lower body power development in preseason preparation of elite rugby union players

Hansen, KT, Cronin, JB, Pickering, SL, Newton, MJ. Does cluster loading enhance lower body power development in preseason preparation of elite rugby union players? J Strength Cond Res 25(8): 2118-2126, 2011—The purpose of this study was to ascertain whether cluster training led to improved power training adaptations in the preseason preparation of elite level rugby union players. Eighteen highly trained athletes were divided into 2 training groups, a traditional training (TT, N = 9) group and a cluster training (CT, N = 9) group before undertaking 8 weeks of lower body resistance training. Force-velocity-power profiling in the jump squat movement was undertaken, and maximum strength was assessed in the back squat before and after the training intervention. Two-way analysis of variance and magnitude-based inferences were used to assess changes in maximum strength and force, velocity, and power values pretraining to posttraining. Both TT and CT groups significantly (p < 0.05) increased maximum strength posttraining. There was a possibly negative effect for the CT group on maximum strength when compared with that for the TT group (pretraining to posttraining change = 14.6 ± 18.0 and 18.3 ± 10.1%, respectively). There were no significant differences pretraining to posttraining for any jump squat force, velocity, or power measures. However, magnitude-based inferences showed that there was a likely positive effect of CT when compared with that of TT for peak power (pretraining to posttraining change = 7.5 ± 7.0 and 1.0 ± 6.2%, respectively) and peak velocity at 40 kg (pretraining to posttraining change = 4.7 ± 6.1 and 0.0 ± 5.0%, respectively) and for peak velocity at body weight (pretraining to posttraining change = 3.8 ± 3.4 and 0.5 ± 3.8%, respectively). Although both a traditional and cluster training loading pattern improved lower body maximum strength in a highly trained population, the traditional training structure resulted in greater maximum strength adaptation. There was some evidence to support the possible benefit of cluster type loading in training prescription for lower body power development.

The reliability of linear position transducer and force plate measurement of explosive force-time variables during a loaded jump squat in elite athletes.

Hansen, KT, Cronin, JB, and Newton, MJ. The reliability of linear position transducer and force plate measurement of explosive force-time variables during a loaded jump squat in elite athletes. J Strength Cond Res 25(5): 1447-1456, 2011-The best method of assessing muscular force qualities during isoinertial stretch shorten cycle lower body movements remains a subject of much debate. This study had 2 purposes: Firstly, to calculate the interday reliability of peak force (PF) measurement and a variety of force-time measures, and, secondly, to compare the reliability of the 2 most common technologies for measuring force during loaded jump squats, the linear position transducer (PT), and the force plate (FP). Twenty-five male elite level rugby union players performed 3 rebound jump squats with a 40-kg external load on 2 occasions 1 week apart. Vertical ground reaction forces (GRFs) were directly measured via an FP, and force was differentiated from position data collected using a PT. From these data, a number of force-time variables were calculated for both the FP and PT. Intraclass correlation coefficient (ICC), coefficient of variation (CV), and percent change in the mean were used as measures of between-session reliability. Additionally, Pearsons product moment correlation coefficients were used to investigate intercorrelations between variables and technologies. Both FP and PT were found to be a reliable means of measuring PF (ICC = 0.88-0.96, CV = 2.3-4.8%), and the relationship between the 2 technologies was very high and high for days 1 and 2, respectively (r = 0.67-0.88). Force-time variables calculated from FP data tended to have greater relative and absolute consistency (ICC = 0.70-0.96, CV = 5.1-51.8%) than those calculated from differentiated PT data (ICC = 0.18-0.95, CV = 7.7-93.6%). Intercorrelations between variables ranged from trivial to practically perfect (r = 0.00-1.00). It was concluded that PF can be measured reliably with both FP and PT technologies, and these measurements are related. A number of force-time values can also be reliably calculated via the use of GRF data. Although some of these force-time variables can be reliably calculated using position data, variation of measurement is generally greater when using position data to calculate force.

Strength, Speed and Power Characteristics of Elite Rugby League Players

Abstract de Lacey, J, Brughelli, ME, McGuigan, MR, and Hansen, KT. Strength, Speed and power characteristics of elite rugby league players. J Strength Cond Res 28(8): 2372–2375, 2014—The purpose of this article was to compare strength, speed, and power characteristics between playing position (forwards and backs) in elite rugby league players. A total of 39 first team players (height, 183.8 ± 5.95 cm; body mass, 100.3 ± 10.7 kg; age, 24 ± 3 years) from a National Rugby League club participated in this study. Testing included 10-, 40-m sprint times, sprint mechanics on an instrumented nonmotorized treadmill, and concentric isokinetic hip and knee extension and flexion. Backs, observed to have significantly (p ⩽ 0.05) lighter body mass (effect size [ES] = 0.98), were significantly faster (10-m ES = 1.26; 40-m ES = 1.61) and produced significantly greater relative horizontal force and power (ES = 0.87 and 1.04) compared with forwards. However, no significant differences were found between forwards and backs during relative isokinetic knee extension, knee flexion, relative isokinetic hip extension, flexion, prowler sprints, sprint velocity, contact time, or flight time. The findings demonstrate that backs have similar relative strength in comparison with forwards, but run faster overground and produce significantly greater relative horizontal force and power when sprinting on a nonmotorized instrumented treadmill. Developing force and power in the horizontal direction may be beneficial for improving sprint performance in professional rugby league players.

The effects of tapering on power-force-velocity profiling and jump performance in professional rugby league players.

Abstract de Lacey, J, Brughelli, M, McGuigan, M, Hansen, K, Samozino, P, and Morin, J-B. The effects of tapering on power-force-velocity profiling and jump performance in professional rugby league players. J Strength Cond Res 28(12): 3567–3570, 2014—The purpose of this study was to investigate the effects of a preseason taper on individual power-force-velocity profiles and jump performance in professional National Rugby League players. Seven professional rugby league players performed concentric squat jumps using ascending loads of 25, 50, 75, 100% body mass before and after a 21-day step taper leading into the in-season. Linear force-velocity relationships were derived, and the following variables were obtained: maximum theoretical velocity (V0), maximum theoretical force (F0), and maximum power (Pmax). The players showed likely-to-very likely increases in F0 (effect size [ES] = 0.45) and Pmax (ES = 0.85) from pre to posttaper. Loaded squat jump height also showed likely-to-most likely increases at each load (ES = 0.83–1.04). The 21-day taper was effective at enhancing maximal power output and jump height performance in professional rugby players, possibly as a result of a recovery from fatigue and thus increased strength capability after a prolonged preseason training period. Rugby league strength and conditioning coaches should consider reducing training volume while maintaining intensity and aerobic conditioning (e.g., step taper) leading into the in-season.

Three Methods of Calculating Force-Time Variables in the Rebound Jump Squat

Hansen, KT, Cronin, JB, and Newton, MJ. Three methods of calculating force-time variables in the rebound jump squat. J Strength Cond Res 25(3): 867-871, 2011-The force-time qualities of the lower limb of athletes have been assessed using a variety of exercises and methodologies. The purpose of this study was to investigate the differences among 3 methods previously used to calculate various force-time measures during a rebound jump squat. Twenty-five professional rugby players performed 3 jump squats, each of which was analyzed using 3 different methods of calculation for a number of force-time variables. Method 1 analyzed the force-time curve from minimum force to maximum force; method 2 analyzed the concentric portion of the force-time curve only; and method 3 analyzed both the eccentric and concentric components of the force-time curve. Significant differences were found (p < 0.001) among all 3 methods of analysis (percent difference 1.1-364.3%) for all the force-time variables calculated. A number of variables had very high (r = 0.76-0.86) or practically perfect (r = 0.93-1.00) correlation coefficients among analysis methods, however, showing similar rank order of the population regardless of the analysis methods used. The results suggested that force-time variables that assess rate of force development relative to peak force produce significantly different values, but these values are highly correlated whether the concentric phase is included in the analysis or the eccentric and concentric phases are included in the analysis. When time-dependent variables are investigated, however, the starting point of calculation results in the measurement of functionally independent physical qualities.

An investigation into the influence of score differential on the physical demands of international women’s rugby sevens match play

ABSTRACT This study explores whether the score differential in winning games influenced the physical demands of match play in women’s rugby seven players. Fifteen members from a highly ranked international team (mean ± SD, 24.3 ± 3.87 years, 168 ± 7.15 cm, 67.5 ± 6.31 kg) participated in this study. Winning score differentials were classified as either small (<21 points) or large (>21 points) and global positional system running data along with match play activities were analysed to identify whether differences exist. Total distances covered were moderately greater in high score differential games (mean difference, ±99% confidence limits, 3.8, ±5.2 m·min−1). Small differences (high – low) were also observed for distance covered at the following speeds: 2–3.5 m·s−1 (1.3, ±3.4 m·min−1), 5–6 m·s−1 (0.8, ±1.5 m·min−1) and ≥6 m·s−1 (1.4, ±1.6 m·min−1). There were a moderately greater numbers of missed tackles (mean count 0.2) and lineouts (mean count 0.5) in low score differential versus high score differential games. Greater winning margins were associated with greater running demands and fewer match activity demands. It is suggested that specific recovery protocols should be considered for matches that have either higher running or match activity demands.