Andrew J. Harrison

The Effect of Resisted Sprint Training on Speed and Strength Performance in Male Rugby Players

Various studies have demonstrated that resistance sprint (RS) training can produce significant changes in running speed and running kinematics. The longer-term training adaptations after RS training remain unclear. The purpose of this study was to investigate whether an RS training intervention would enhance the running speed and dynamic strength measures in male rugby players. Fifteen male rugby players aged 20.5 (+/- 2.8) years who were proficient in resisted sledge training took part in the study. The subjects were randomly assigned to control or RS groups. The RS group performed two sessions per week of RS training for 6 weeks, and the control group did no RS training. Pre- and postintervention tests were carried out for 30-m sprint, drop, squat, and rebound jumps on a force sledge system. A laser measurement device was used to obtain velocities and distance measures during all running trials. The results show a statistically significant decrease in time to 5 m for the 30-m sprint for the RS group (p = 0.02). The squat jump and drop jump variables also showed significant increases in starting strength (p = 0.004) and height jumped (p = 0.018) for the RS group from pre- to post-testing sessions. The results suggest that it may be beneficial to employ an RS training intervention with the aim of increasing initial acceleration from a static start for sprinting.Wilcock, IM, Whatman, C, Harris, N, and Keogh, JWL. Vibration training: could it enhance the strength, power, or speed of athletes? J Strength Cond Res 23(2): 593-603, 2009-The aim of this literature review was to determine whether vibration training could produce chronic improvements in the physical performance of trained athletes. Although the main objective was to analyze any performance benefits, a brief review of possible mechanisms linked to performance enhancement is also included. Vibration causes an increase in the g-forces acting on the muscles, increasing the loading parameters of any exercise. Increased loading should aid muscle hypertrophy, and some authors have suggested that vibration may enhance neuromuscular potentiation. Considering the 6 studies on trained athletes, there does seem to be some evidence to suggest that vibration may provide a small benefit to maximal strength (1-repetition maximum) and power (countermovement jumps) of trained athletes. Speed does not seem to be enhanced by vibration training. There is a lack of evidence to support the theory that long-term vibration training increases neuromuscular potentiation in trained athletes. What mechanism(s) could be responsible for possible strength and power enhancement is unclear. Because whole-body vibration does not seem to be detrimental to performance when used in a controlled manner, it could provide an additional training stimulus for athletes. However, further research is required to determine optimum vibration training protocols and to clarify whether vibration training produces performance benefits greater than those of traditional training methods.

Force-Velocity Relationship and Stretch-Shortening Cycle Function in Sprint and Endurance Athletes

&NA; Harrison, A.J., S.P. Keane, and J. Coglan. Forcevelocity relationship and stretch‐shortening cycle function in sprint and endurance athletes. J. Strength Cond. Res. 18(3):473–479. 2004.—This study examined the torque‐velocity and powervelocity relationships of quadriceps muscle function, stretch shortening cycle function, and leg‐spring stiffness in sprint and endurance athletes. Isokinetic maximal knee extension torque was obtained from 7 sprinters and 7 endurance athletes using a Con‐trex isokinetic dynamometer. Torque and power measures were corrected for lean‐thigh cross‐sectional area and lean‐thigh volume, respectively. Stretch‐shortening cycle function and muscle stiffness measurements were obtained while subjects performed single‐legged squat, countermovement, and drop‐rebound jumps on an inclined sledge and force‐plate apparatus. The results indicated that sprinters generated, on average, 0.15 ± 0.05 N·m·cm‐2 more torque across all velocities compared with endurance athletes. Significant differences were also found in the power‐velocity relationships between the 2 groups. The sprinters performed significantly better than the endurance athletes on all jumps, but there were no differences in prestretch augmentation between the groups. The average vertical leg stiffness during drop jumps was significantly higher for sprinters (5.86 N·m‐1) compared with endurance runners (3.38 N·m‐1). The findings reinforce the need for power training to be carried out at fast contraction speeds but also show that SSC function remains important in endurance running.

THE OPTIMAL COMPLEX TRAINING REST INTERVAL FOR ATHLETES FROM ANAEROBIC SPORTS

Comyns, T.M., A.J. Harrison, L.K. Hennessy, and R.L. Jensen. The optimal complex training rest interval for ath- letes from anaerobic sports. J. Strength Cond. Res. 20(3):471- 476. 2006.—Complex training research has indicated that 3-4 minutes may be an optimum intracomplex rest interval. The purpose of this study was to determine if a heavy resistive ex- ercise causes performance enhancement of a slow stretch-short- ening cycle exercise and if there is an optimal rest interval. Eighteen subjects performed countermovement jumps (CMJs) before and after a 5 repetition maximum back squat lifting pro- tocol. This procedure was repeated 4 times over 2 days using rest intervals of 30 seconds and 2, 4, and 6 minutes. Flight time and peak ground reaction force (GRF) were the dependent var- iables. All jumps were performed on a specially constructed sledge and force platform apparatus. Repeated measures anal- ysis of variance found a significant reduction in flight time at the 30-second and 6-minute interval (p 0.05). No significant difference was found between men and women. Only the men showed an enhancement in jump performance after the 4-min- ute interval. The improvement window was different for each subject, and an analysis of the greatest increase and decrease in flight time and peak GRF was conducted, showing a significant decrease for men and women and a significant increase in flight time for men and peak ground reaction force for women. The results suggest that complex training can benefit or inhibit CMJ performance depending on the rest interval. The individual de- termination of the intracomplex rest interval may be necessary in the practical setting.

Functional Data Analysis of Running Kinematics in Chronic Achilles Tendon Injury

PURPOSE Chronic Achilles tendon (AT) injuries are common, but kinematic studies confirming the exact mechanisms of injury and how orthoses are effective are lacking. Existing analysis often relies on discrete measures and provides an incomplete analysis because many of the data are discarded. Functional data analysis (FDA) views the entire dataset as a function, thus retaining the main features of the curve. This study uses FDA to examine the mechanisms of chronic AT injury and the functional effects of orthoses. METHODS Twelve subjects with a history of chronic AT injury and 12 controls ran on a treadmill with and without customized orthoses. Three-dimensional kinematic data were obtained using Qualisys motion capture systems operating at 200 Hz. Ankle dorsiflexion (ADF), knee flexion (KF), eversion (EV), calcaneal, and leg abduction angles were calculated across stance. These angle data were represented as functions, and functional principal components were extracted to describe the factors accounting for variation in the data. These components were compared in AT versus control groups and orthoses versus no-orthoses conditions. RESULTS Kinematic differences were observed, with the AT group showing greater EV, ADF, and KF during stance, whereas orthoses reduced ADF but increased EV. Different patterns of frontal plane variation distinguished between groups and conditions. CONCLUSION Results provided additional information about movement patterns compared to traditional approaches and identified the first half of stance as the most relevant period in injury occurrence. The study showed evidence that variability is related to the presence of injury in this clinical population. Further FDA focusing on within-subject variation is recommended to gain greater insight into the role of variability in injury occurrence.

Movement variability and skills monitoring in sports

The aim of this paper was to present a review on the role that movement variability (MV) plays in the analysis of sports movement and in the monitoring of the athletes skills. MV has been traditionally considered an unwanted noise to be reduced, but recent studies have re-evaluated its role and have tried to understand whether it may contain important information about the neuro-musculo-skeletal organisation. Issues concerning both views of MV, different approaches for analysing it and future perspectives are discussed. Information regarding the nature of the MV is vital in the analysis of sports movements/motor skills, and the way in which these movements are analysed and the MV subsequently quantified is dependent on the movement in question and the issues the researcher is trying to address. In dealing with a number of issues regarding MV, this paper has also raised a number of questions which are still to be addressed.

Identifying the optimal resistive load for complex training in male rugby players

Alternating a resistance exercise with a plyometric exercise is referred to as “complex training”. In this study, we examined the effect of various resistive loads on the biomechanics of performance of a fast stretch–shortening cycle activity to determine if an optimal resistive load exists for complex training. Twelve elite rugby players performed three drop jumps before and after three back squat resistive loads of 65%, 80%, and 93% of a single repetition maximum (1-RM) load. All drop jumps were performed on a specially constructed sledge and force platform apparatus. Flight time, ground contact time, peak ground reaction force, reactive strength index, and leg stiffness were the dependent variables. Repeated-measures analysis of variance found that all resistive loads reduced (P < 0.01) flight time, and that lifting at the 93% load resulted in an improvement (P < 0.05) in ground contact time and leg stiffness. From a training perspective, the results indicate that the heavy lifting will encourage the fast stretch–shortening cycle activity to be performed with a stiffer leg spring action, which in turn may benefit performance. However, it is unknown if these acute changes will produce any long-term adaptations to muscle function.

Motor development and gender effects on stretch-shortening cycle performance

A substantial part of human movement such as jumping, hopping, leaping and other bounding movements are improved by making a counter-movement. These activities are often described as stretch shortening cycle (SSC) movements. The aim of this study was to determine whether the SSC affects performance in vertical jump in children to the same extent as it does in adults. Comparisons were made between counter-movement jump (CMJ) and squat jump (SJ) performance in children and adults. The ratio of take-off velocity between jumps was used to measure performance of the SSC. Two groups of subjects comprising of 22 adults and 20 children performed three CMJs and three SJs from a force platform. Impulse, take-off velocity and power were obtained by numerical integration of the force n time traces. Performance was calculated from the velocity at take off. Both groups jumped significantly higher in the CMJ but there was a higher degree of variability in the performance of the children. The results indicated that children could utilise a SSC to enhance jumping performance. Variability in the take-off velocities in children, particularly in the SJ suggests the children performed this jump non-optimally.

Postural Instability in Diabetic Neuropathic Patients at Risk of Foot Ulceration

Diabetic peripheral neuropathy is believed to cause postural instability due to abnormal proprioception. We assessed body sway in four groups, each of 20 subjects, matched for age, sex, and BMI: non‐diabetic controls, non‐neuropathic diabetic controls, subjects with diabetic neuropathy and no history of foot ulceration, and subjects with diabetic neuropathy and a history of foot ulceration. Postural sway was assessed on a Kistler force plate using the Romberg test, measuring the standard deviation of the centre of pressure in both sagittal (antero‐posterior movement) and frontal (side to side movement) planes with eyes open and closed. The Romberg test results were log transformed and then analysed using analysis of variance followed by Newman‐Keuls test. There was no significant difference in body sway between the two control groups and the first group of subjects with diabetic neuropathy. However, in patients with a history of ulceration, values were significantly higher (p < 0.05) compared to all other groups in both planes and conditions studied. These results are suggestive of a relationship between impaired body sway control and foot ulceration. Postural instability may have clinical significance and increase the risk of minor trauma and ulceration in patients with diabetic neuropathy.

Lower limb kinematics of subjects with chronic achilles tendon injury during running.

This study examined the kinematic differences between subjects who had a history of chronic Achilles tendon (AT) injury and matched controls during running. Eleven subjects from each group ran barefoot (BF) and shod at self-selected speeds on a treadmill. Three-dimensional angles describing rearfoot and lower limb motion were calculated throughout stance. Five footfalls were obtained for each subject and condition. Pairwise comparisons revealed greater eversion, ankle dorsiflexion and less leg abduction during stance in the AT group compared with controls. Running kinematics were exaggerated in shod compared with BF conditions, as expected from previous research. The differences between conditions were more exaggerated in AT subjects compared with control subjects. Further analysis using a curve-based approach is recommended.

Functional data analysis of knee joint kinematics in the vertical jump

Abstract Understanding of the motor development process is usually based on descriptive studies using either cross‐sectional or longitudinal designs. These data typically consist of sets of measurements on groups of individuals gathered during the performance of a single task. A natural approach is to represent the set of measurements for an individual as a single entity, a function. In practice, however, this approach is seldom applied. Typically, the analysis proceeds by reducing what are intrinsically functional responses to a single summary measurement and then using this to draw conclusions. As a result, many potentially informative data are ignored. Functional data analysis (FDA) is an emerging field in statistics that focuses on treating an entire sequence of measurements for an experimental unit as a single function. Therefore, functional data analysis appears to be inherently suitable for analysing kinematic data. In this paper, the key concepts and procedures of functional data analysis are introduced and illustrated using data obtained from a cross‐sectional study on the development of the vertical jump.