The temporal pattern of recovery of eccentric hamstring strength and dynamic stability in elite footballers

Recent epidemiological data suggests that the incidence of hamstring and ACL injuries are on the rise in football, resulting in significant financial costs to individual clubs. Research has highlighted fatigue, decreased functional strength and reduced dynamic stability as key aetiological factors common to both injuries. Previous research has considered the influence of fatigue on eccentric strength and dynamic stability discretely, but their functional synergy warrants investigation. Furthermore, the fatigue-effect should be considered beyond the acute 90 minutes of match exposure, and consider the temporal pattern of recovery. In the first experimental chapter (Chapter 4), twenty male professional soccer players (age 21.50 ± 3.09 years, height 181.98 ± 5.43cm, body mass 77.73 ± 5.06 kg), undertook a localised fatigue protocol until they exhibited a 30% reduction in eccentric hamstring peak torque. Pre fatigue measures of isokinetic eccentric strength (60°·s-1, 150°·s-1, 300°·s-1., System 3, Biodex Medical Systems, Shirley, NY, USA) and dynamic stability (OSI – Overall Stability Index, A-P – Anterior Posterior Stability, M-L – Medial Lateral Stability, Biodex Medical Systems, Shirley, NY) were taken. These were then repeated at the same time of day post, 24 hr post, 48 hr post and 72 hr post fatigue. Metrics in average peak torque and peak torque were observed to be significantly reduced (P ≤ 0.05) when compared to baseline levels at +72 hr at the two fastest testing speeds. Significance values indicated that angle of peak torque was fully recovered. Dynamic stability measures of OSI and A-P also remained significantly reduced (P ≤ 0.05) at +72 hr, whereas M-L scores showed no significance (P ≥ 0.05) at 72 hr. Quadratic regression analyses revealed unique temporal rates of recovery, requiring up to +82 hr post-exercise. These unique patterns were identified through differentiation of the quadratic regression curve, enabling calculation of the curve minima and the time at which the outcome variable returned to pre-exercise levels. A similarexperimental design was employed in Chapter 5, utilising a soccer-specific fatigue protocol. Eighteen male professional soccer players completed the present study, with a mean age of 22.94 ± 4.57 years, height 185.38 ± 4.22cm and body mass 75.91 ± 6.38 kg. Average peak torque and peak torque metrics at all speeds were significantly reduced (P ≤ 0.05) at +72 hr, with no change in angle of peak torque. As with the localised fatigue protocol, dynamic stability measures in A-P were significantly impaired at +72 hr (P ≤ 0.05) whereas M-L scores were recovered to baseline at 72 hrs. A similar predicted maximum recovery duration of +81 15 hr was observed following soccer-specific exercise, utilising the same quadratic regression analysis as in chapter 4.Fourteen male professional soccer players completed chapter 6, (mean age 24.29 ± 5.06 years, height 184.51 ± 3.91cm, and body mass 74.91 ± 4.30 kg) analysing the effects of soft tissue massage (24 hours post fatigue) on the temporal pattern of recovery post soccer specific fatigue. Sports massage techniques were applied for 20 minutes on the posterior aspect of the dominant limb, with a specific focus on effleurage and petrissage to aid recovery. Results highlighted that all measures for AvgPkTeccH, PkTeccH (60°·s-1, 150°·s-1 and 300°·s-1.) and OSI were all shown to recover within the 72 hr period. The A-P dynamic stability measures were recovered at +48 hr. Time of recovery was calculated with the same quadratic regression anlaysis completed in chapters 4 and 5. These findings indicate that an intervention of soft tissue massage at 24 hr post fatigue accelerates the recovery process. An alternate intervention was utilised in Chapter 7, where sixteen male professional soccer players completed a soccer specific fatigue protocol incorporating periods of interchange (mean age 22.64 ± 4.70 years, height 185.41 ± 4.72cm, body mass 77.62 ± 6.08 kg). The interchange strategy employed was designed to reduce total workload (to 60mins), with each player exposed to a 15 min period of rest in the middle of each half. Peak torque metrics at the two slowest speeds had failed to attain full recovery at +72 hrs, and similarly OSI was still significantly impaired relative to baseline at +72 hrs. Following completion of the same quadratic regression analysis, as completed in previous chapters (4, 5 and 6) the predicted time required for full recovery of all markers was +82 hr. The results of the study highlight that despite reducing the playing time with periods of interchange players had still not fully recovered within the 72 hr period, thus exposing players to potential injury within this time period The current thesis is aimed at the sports science and medical teams working within football involved in injury prevention strategies, specific conditioning and rehabilitation. Findings highlight the temporal pattern of recovery post-exercise with specific focus on hamstring function. Simple functional anatomy highlights any decreased function of the hamstring will have implications for potential knee injury, including the ACL. Epidemiological and aetiological research in football continues to be heavily focussed on hamstring strains. This thesis highlights the potential implications that decreased function over a 72 hr period can have on the muscle group, and associated ligamentous structures. Clinical implications of this work 16 include the periodisation of rehabilitation stages or training micro-cycles, the importance of developing fatigue resistance within players to facilitate a reduction in the occurrence of hamstring and ACL injury, and the development of a more stringent return to play criteria encompassing these biomechanical markers. Evidently, findings within the current body of work suggest that fatigue is an unalterable factor that contributes to injury, but it can be quantified with meaures of dynamic stability and eccentric strength. Quantifying fatigue between games with these biomechanical markers provides key information of a player’s readiness to play, implications for injury, key time frames to implement interventions and provide key markers to be utilised in the design of return to play protocols post injury.