Muscular Fatigue: Methods for Assessing fatigue and Implications for Anterior Cruciate Ligament (ACL) Injury.

1. Muscular Fatigue: Methods for Assessing fatigue and Implications for Anterior Cruciate Ligament (ACL) Injury. Paul Rimmer, (BSc, MSc). Post-Graduate Research Student School of Healthcare Studies.

2. Presentation Overview. • What is fatigue and how it can be categorised? • What causes fatigue? • Methods for inducing fatigue. • How do we assess fatigue level? • The effect of fatigue on biomechanics in healthy and ACL injured people. • Why is measuring the effect of fatigue on ACL injured people important?

3. Fatigue and Injury. • Fatigue has been implicated as a potential indicator for injuries in several sports. • Injury rates tend to increase towards the end of games. • Importance of pre-habilitation and rehabilitation.

4. What is Fatigue? • ‘Any reduction in the force generating capacity of the total neuromuscular system regardless of the force required in any given situation’ (Bigland-Ritchie and Woods,1984). • The two main types of physiological fatigue are defined as ‘central’ and ‘peripheral’ fatigue. • Central fatigue is influenced primarily by mechanisms affecting the neuromuscular system at a level above the neuromuscular junction. • Peripheral fatigue is influenced by mechanisms affecting muscle and contractile tissues.

5. What Causes Fatigue? • Peripheral fatigue: A reduction in muscle force due to the direct or indirect effects of the reduction of energy and substrates or accumulation of metabolites within the muscle fibres. • Central fatigue: The mechanism(s) involved in central fatigue remain unknown. • Central fatigue can be considered a safety precaution to maintain the function of various organs. • It is known to be influenced by low blood glucose and high temperature.

6. Functional (Open Chain) Methods. Running. Squatting. Jumping. Individually or in combination. Closed Chain Methods. Weight training machines. A set number of repetitions at %age of 1 rep max. Isokinetic Dynamometry. Multiple set up options using speed of movement, force, muscle action and range of movement. Methods for Inducing Fatigue.

7. Measuring Fatigue Levels. • Functional Protocols: Volitional Fatigue, Rate of Perceived Exertion, Loss of functional performance. • Weight Machines: Volitional fatigue. • Isokinetic Dynamometry: As above BUT can quantify end point of fatigue more accurately and calculate fatigue rate.

8. Effect of Fatigue on Biomechanics in Healthy Populations. • Limited studies on dynamic movements such as jump landing, hopping and cutting. • Most research carried out on drop-jump landings. • Comparing pre to post-fatigue conditions, the priority seems to be maintenance of knee joint stability. • Compensation strategies include increase in hip and ankle work.

9. Effects of Fatigue of Biomechanics in ACL Injured Participants. • Studies in this area are scarce: There are presently..... • 0!! Two main reasons for this. • Fear of Injuring Participants. • Lack of Clinical Expertise in the Research Setting. BUT.. We know some ACL injured patients in un-fatigued conditions show compensation strategies that are centred around knee joint stability and increased hip and ankle work.

10. Why is Measuring the Effect of Fatigue on ACL injured people Important? • Clinically a persons fatigue resistance/endurance is not effectively measured. • Therefore there is no assessment of the patients ability to perform dynamic tasks whilst fatigued. • Fatigue should be considered in the rehabilitation progress to guide decisions on return to activities. • We do not currently understand how or if fatigue effects ACL injured peoples movements.

11. Key Questions. • Do ACL injured patients show deficits in terms of fatigue resistance compared to uninjured people? • Do ACL injured people use different movement patterns in a fatigued state compared to uninjured people? • If so, does this put them at risk of re-rupture or further structural damage?

12. References: • CHAPPELL, J. D., HERMAN, D. C., KNIGHT, B. S., KIRKENDALL, D. T., GARRETT, W. E. & YU, B. (2005) Effect of fatigue on knee kinetics and kinematics in stop-jump tasks. American Journal of Sports Medicine, 33, 1022-9. • COVENTRY, E., O'CONNOR, K. M., HART, B. A., EARL, J. E. & EBERSOLE, K. T. (2006) The effect of lower extremity fatigue on shock attenuation during single-leg landing. Clinical Biomechanics, 21, 1090-1097. • KELLIS, E. & KOUVELIOTI, V. (2009) Agonist versus antagonist muscle fatigue effects on thigh muscle activity and vertical ground reaction during drop landing. Journal of Electromyography & Kinesiology, 19, 55-64. • KERNOZEK, T. W., TORRY, M. R. & IWASAKI, M. (2008) Gender differences in lower extremity landing mechanics caused by neuromuscular fatigue. American Journal of Sports Medicine, 36, 554-565. • ORTIZ, A., OLSON, S. L., ETNYRE, B., TRUDELLE-JACKSON, E. E., BARTLETT, W. & VENEGAS-RIOS, H. L. Fatigue effects on knee joint stability during two jump tasks in women. Journal of Strength and Conditioning Research, 24, 1019-1027. • VERBITSKY, O., MIZRAHI, J., VOLOSHIN, A., TREIGER, J. & ISAKOV, E. (1998) Shock transmission and fatigue in human running. Journal of Applied Biomechanics, 14, 300-11. • WIKSTROM, E. A., POWERS, M. E. & TILLMAN, M. D. (2004) Dynamic stabilization time after isokinetic and functional fatigue. Journal of Athletic Training, 39, 247-253. • WOJTYS, E., WYLIE, B. & HUSTON, L. (1996) The effects of muscle fatigue on neuromuscular function and anterior tibial translation in healthy knees. American Journal of Sports Medicine, 24, 615-21.

13. Thank you for your time… Any Questions??