Strength: ‘Peak torque’ measured from eccentric/concentric quadriceps/hamstrings using a Kincom isokinetic dynamometer (fig.4). The subjects’ right leg was used. Angular velocity was set at 60 degrees/sec. seat angle set at 15 degrees, start angle knee 90 degrees of knee flexion, the moment arm was 37 cm, and the subjects’ leg weighed 77N.
The ability to generate and accept maximal forces have been suggested to be key components of agility (Newman, et. al., 2004).
Fig.4 Isokinetic strength testing using Kincom.
Technique: A 5 metre agility sprint was performed; the subject was instructed to plant their right leg straight at contact into the turn. An AMT1 force platform measured peak braking,peak drive off forces at the turn. Time taken was measured using the Laveg speed gun, a Sony camcorder filmed the subject from the side and the turn was analysed using a high speed troubleshooter video camera at 125 frames per second. The subject performed a 180 degree turn (right leg). Quintic (version 9.09) software used to quantify the technique variables.
Fig 5. Analysis of technique using Quintic software.
Results
Table 1. Subject results pre & post intervention & comparisons with normative data (Graham-Smith and Pearson, 2005).
Interpretation and Recommendations
The subject was evaluated using the data gained in the quantitative tests (table 1) and comparisons were made to normative data (Buttifant et al., 1999; Graham-Smith and Pearson, 2005). Multiple regression equations (MRE) were calculated (appendices) from the normative data values found in the study by Graham-Smith and Pearson (2005). MRE were used to predict total time taken in the 5 metre agility sprint and predict the contact time of the turn. The subjects’ technical abilities were also measured qualitatively by applying a technical framework analysis (see appendices).
The subjects’ agility test times were already classed as excellent in comparison to the normative data, although the contact time could be improved further and is a significant variable of agility performance (Graham-Smith and Pearson, 2005). This variable plus the subjects’ last stride length and leg plant angle were the other variables identified that would link to an improved agility time. A shorter last stride length with a greater leg plant angle should reduce contact time and total agility performance time as predicted by the MRE calculated from the normative data (Graham-Smith and Pearson, 2005).
Fig.6. Last stride length and inclining the trunk backwards
For coaching purposes the technique analysis framework can then be referred to employ the relevant coaching points related to biomechanical principles which will improve the sub-phase of the movement and improve performance.
The subjects’ strength data was considered sufficient to allow for improvement and be capable of accepting forces without the risk of injury, as identified by using the dynamic control ratio proposed for eccentric hamstrings/concentric quadriceps strength (Graham-Smith and Lee, 2002).
The poorest results gained from the subjects’ quantitative data were related to balance and proprioception, however the intervention ignored these variables as they have been shown to be poorly correlated with high agility performance (Graham-Smith and Pearson, 2005).
Although the intervention did not aim to improve the subjects’ average balance and proprioception it must be recognized that by improving these variables there is a reduced risk of ACL and ankle injuries (Wedderkopp et al., 1999; Myklebust et al., 2003; Hewtt et al., 2006). The subjects’ speed time was found to be average when compared to normative data; the likelihood of improving it a significant amount to affect agility performance in three half hour sessions is very unlikely.
Recommendations
- Prior to leg plant for turn apply a pre-brake step to reduce brake step forces, friction and reduce brake-step contact time.
- Incline the trunk backwards to increase braking stability, lower centre of mass and sudden deceleration.
- Reduce last stride length to aid sudden deceleration, reduce contact time.
- Flex more at knee on contact at foot plant to aid sudden deceleration, lower centre of mass.
- Plant trailing leg and flex knee and trunk to improve acceleration out of the turn (fig.7).
Fig.7. Flexion of trunk and knee
Intervention and Conclusion
The intervention was carried out over three half hour sessions, the main focus of the sessions were to improve upon the technical variables as given in the recommendations. To aid in coaching the sessions a camcorder was used to film technique so it could be played back to the subject and provide valuable feedback to aid learning. Each session was aimed at coaching two elements of the agility turn. Each element was broken down and performed on its own many times; gradually as the subject improved it was performed at speed and then as part of the whole ‘agility turn.’
On the first session we dealt with the subjects’ preparation into the turn, the subject was noticed on the test to be stood very upright at the start, to improve acceleration he was asked to crouch lower.
The other element to the session was to encourage the subject to use a pre-brake step to reduce force on main brake-step and reduce contact time and friction.
Fig.8. Improving acceleration pre/post
In the second session the pre-brake step was reinforced paying particular attention to shortening the last stride and the main brake-step was focused upon. The subject was encouraged to incline the trunk backwards at contact and flex at the knee more upon contact.
Fig.9. Brake-step. Improved trunk angle and knee flexion. Pre/post
Finally the third session worked on from the brake-step, lifting the trailing leg whilst turning and lowering centre of mass to aid acceleration out of the turn.
Fig.10. Acceleration out of the turn. Pre/post
On reflection the intervention strategy was successful as last stride length and contact time was reduced, greater knee angle flexion was achieved and through the product of this total agility time was superior. The intervention strategy though did fail to improve the subjects’ trunk angle and leg plant angle at contact, in fact they were worst. This could be because the subject was given too many elements to improve upon, the subject did express the view that there was too much to think about during sessions. This may be due to the relative inexperience of the coaches and their structure of sessions or a failure to communicate in a clear and concise way with the subject. The coaches must therefore break each element of technique down precisely using tools like the technique framework and allow athletes enough time to perfect the execution, before building the movement back up again.
Even though the subjects’ agility performance improved it could be argued that it was nothing to do with the intervention by the coaches, and that through practice and improved neuromuscular pathways and task familiarisation they would have improved anyway.
Future recommendations would imply trail research be conducted where comparisons with a control group can be made.
The MRE used proved to be extremely valuable, they pretty accurately illustrate the key factors of agility performance and how importantly related each variable is to overall agility performance. The MRE eliminate any guesswork by coaches, trainers and rehabilitators and are an effective tool that could be implemented to improve successful performance.
Total word count 2,304
Actual word count 1,924
References
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Graham-Smith, P. and Lee, A. (2002). Risk Assessment of Hamstring injury in Rugby Union place kicking. 4th World Congress of Science and Football, Sidney, Australia, 22nd-26th February 1999, p182-189. Cambridge University Press, Taylor and Francis Group.
Graham-Smith, P. and Pearson, S.J. (2005). Determinants of Agility Performance. Paper presented to the Biomechanics of the lower limb in health, disease and rehabilitation conference. University of Salford. 5th-7th September, 2005.
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Sheppard, J.M., and Young, W.B. (2006). Agility literature review: Classifications, training and testing. Journal of Sports Sciences. 24, (9). 919-932.
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Secondary References
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Appendices
Technique Analysis for Changing Direction
Multiple Regression Equations
Test data
Total Time =1.24
+0.637 x (2.633) Time 0-15m
+0.978 x (0.56) Contact Time
-0.001 x (362.3) Ecc. Strength
= Predicted Time = 3.10s
= Actual Time 2.865s
= Difference 0.237s
Retest data
Total Time =1.24
+0.637 x (2.55) Time 0-15m
+0.978 x (0.33) Contact Time
-0.001 x (445) Ecc. Strength
= Predicted Time = 3.18s
=Actual Time 2.55s
= Difference 0.60s
Contact Time = 0.119
+ 0.005 x (131) Knee angle Maximum Knee Flexion
+ 0.351 x (0.18) Last Stride length
- 0.360 x ( 0.973) Peak Drive off force / Body Weight
- 0.003 x (21) Trunk angle Touch Down
= Predicted contact time = 0.4239s
= Actual contact time = 0.33s
= Difference = 0.09s
The chart on the next page is from Graham-Smith, P. and Pearson, S.J. (2005), showing normative data for athletes. Our subjects pre-intervention or test data scores are typed in orange and the post-intervention test data is typed in green.
Multiple Regression Equations
Test data
Total Time =1.24
+0.637 x (2.633) Time 0-15m
+0.978 x (0.56) Contact Time
-0.001 x (362.3) Ecc. Strength
= Predicted Time = 3.10s
= Actual Time 2.865s
= Difference 0.237s
Retest data
Total Time =1.24
+0.637 x (2.55) Time 0-15m
+0.978 x (0.33) Contact Time
-0.001 x (445) Ecc. Strength
= Predicted Time = 3.18s
=Actual Time 2.55s
= Difference 0.60s
Contact Time = 0.119
+ 0.005 x (131) Knee angle Maximum Knee Flexion
+ 0.351 x (0.18) Last Stride length
- 0.360 x ( 0.973) Peak Drive off force / Body Weight
- 0.003 x (21) Trunk angle Touch Down
= Predicted contact time = 0.4239s
= Actual contact time = 0.33s
= Difference = 0.09s