The influence of soccer-specific fatigue on the risk of thigh injuries

in amateur Black South African players

Robert JONES (M.Sc.) and Andrew TODD (M.Sc.)

Department of Human Kinetics and Ergonomics, Rhodes University

Grahamstown

SOUTH AFRICA

SASReCon, 5th-8th October 2014, Potchefstroom

Introduction

Hamstring muscle group = most frequently injured anatomical structure in soccer

Commonly occur during rapid extension on the knee- requires eccentric action from the hamstrings

Muscular fatigue identified as a key factor in injury causation

Reduced ability to generate force (due to fatigue) = altered sprint mechanics = increased risk of thigh injury

Soccer-specific fatigue research focused exclusively on;

- European players

- North American players

- South American Players

- No research within an African context

Introduction (cont.)

Black African vs. Caucasian endurance athletes:

- Similar VO2max

- But: Higher fractional VO2max utilization and better running

economy

Epidemiological studies (Verrall et al., 2001; Woods et al., 2004)

- Increased risk of hamstring injuries in players of Black origin

- Attributed to: Greater predominance of Type II muscle fibres

Differences may elicit unique thigh injury risk profiles

Effect of ethnicity on injury risk is unclear

Introduction (cont.)

Therefore: The current study investigated the biomechanical and physiological responses of amateur Black South African players to a 90 minute soccer-specific simulation protocol.

Methods

Participants:

- 20 Black South African males (amateur)

Match-play simulation protocol

Soccer-specific aerobic field test (SAFT90):

- Developed and validated by Lovell et al. (2008)

- 90 minute simulation replicates physiological and mechanical demands of competitive match-play

Adapted from Small et al. (2010)

Methods (cont.)

Heart Rate:

- Recorded at 15 minute intervals

Isokinetics:

- Peak torque (PT) measured in knee flexors and knee extensors

- Testing speeds: 60°.s-1 and 180°.s-1

- Both concentric and eccentric modalities

- Both dominant and non-dominant limbs

- EccH PT and ConQ PT used to calculate functional strength ratio (eccH:conQ)

Isokinetic test 1st half Isokinetic test Half time Isokinetic test 2nd half Isokinetic test

T0 45 mins T45 15 mins T60 45 mins T105

Results

Heart Rate:

1st half 2nd half

162 (±13) bt.min-1 160 (±15) bt.min-1

Where: HR=Heart rate (Adapted from Lovell et al., 2008)

Results (cont.)

Isokinetics: Eccentric Hamstrings PT17.34% 18.27%

Eccentric hamstrings peak torque (Nm) in both the dominant (D) and non-dominant (ND) limb, at isokinetic speeds of 60°.s-1 and 180°.s-1

Results (cont.)

10.04%

Isokinetics: Functional strength ratio (eccH:conQ)

Functional H:Q ratio in both the dominant (D) and non-dominant (ND) limb, at isokinetic speeds of 60°.s-1 and 180°.s-1

Discussion

The SAFT90 protocol indicated to reduce the capacity of the knee flexor and extensor muscles to develop force.

Changes in EccH and functional H:Q support epidemiological data

- HSI more likely during latter stages of both halves

Decline in EccH strength due to eccentric loading from intermittent activity profile

- constant changes in speed + direction = eccentric fatigue

Therefore: Insufficient EccH strength during late swing phase

= eccentric overload = MUSCLE DAMAGE!

Injury risk in dominant limb = non-dominant limb

Discussion (cont.)

NB: Comparisons difficult due to varying experimental designs

Eccentric hamstring strength

- 60°.s-1: 17.34% in EccH PT in agreement with;

• Greig (2008)- 18.10% [Professional/European]

- 180°.s-1: 18.27% in EccH PT in agreement with;

• Greig (2008)- 18.80%

• Greig and Siegler (2009)- 18.00% [Professional/European]

- Values similar to those of numerous authors while at 120°.s-1;

• Rahnama et al. (2003)- 16.80% [Amateur/European] • Small et al. (2010)- 16.80% [Semi-Prof/European] • Lovell et al. (2011)- 20.65% [Semi-Prof/European]

Discussion (cont.)

Functional strength ratio (eccH:conQ)

- 60°.s-1: No significant time effect overall in agreement with;

• Greig (2008) [Professional/European]

- 180°.s-1: 10.04% in H:Q in agreement with;

• Greig (2008)- 22.86%

- Similar decrements observed at 120°.s-1 in amateur and semi-professional Caucasian players;

• Rahnama et al. (2003)- 12.99% [Amateur/European] • Small et al. (2010)- 15.00% [Semi-Prof/European]

Conclusion

EccH and functional H:Q deteriorated over time

Indicate insufficient EccH strength during late swing

- during final stages of both halves

Negative implications for performance + injury risk

Amateur Black African players: Similar rate of eccentric hamstring fatigue as Caucasians, regardless of playing level

- Exposed to similar risks of hamstring injury during match-play

Prevention strategies need to consider resistance to eccentric fatigue of the hamstrings

- maintain H:Q ratio = reduce injury risk

References

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Contact Details

rijones88@gmail.com

Tel: +27 (0) 82 440 2771

Acknowledgements: Andrew Todd (supervisor)Candice Christie (HoD)CATHSSETA