1. Robert JONES (M.Sc.) and Andrew TODD (M.Sc.)
SASReCon, 5th-8th October 2014, Potchefstroom
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

2. 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
The thigh, and more specifically the hamstrings muscle group, are recognised as the most frequently injured anatomical structure in soccer.
Hamstring injuries commonly occur when sprinting, during the rapid extension of the knee which requires eccentric action from the hamstrings in order to slow the lower leg in the late swing phase
A number of possible causes of hamstring injury have been suggested, however muscular fatigue has been identified as a key factor in thigh injury causation.
This explains the greater incidence of injury observed in the later stages of both halves of play.
If the hamstrings ability to produce muscular force is impaired by the onset of fatigue, then the altered mechanics of the sprinting gait cycle are suggested to increase the risk of thigh injury.
Soccer-specific fatigue research has focussed exclusively on European, North American and South American players.
With no research focussed on the strength profiles and the risk of thigh injury within an African context.

3. 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
Although Black African athletes and their Caucasian counterparts have been found to have similar VO2max values, Black African endurance runners have been observed to have a higher fractional VO2max utilisation as well as a superior running economy.
While epidemiological studies have indicated that players of Black ethnic origin may be at a greater risk of sustaining a hamstring injury than their Caucasian counterparts. These authors suggest that players of African origin may have a greater predominance of type II (fast twitch) muscle fibres, resulting in increased risk of hamstring muscle strain due to fatigue.
These differences may elicit unique fatigue and hamstring injury risk profiles in Black African players , different from those of European and American players.
And overall, the effect of ethnicity on injury risk is unclear

4. 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.
Therefore; the present study aimed to assess the biomechanical and physiological responses of amateur Black South African players to a 90 minute soccer match-play simulation protocol.

5. 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
20 Black African male amateur soccer players were recruited for participation in the present study
These participants performed the 90 minute soccer-specific aerobic field test (also known as the SAFT90 protocol).
The simulation was developed and validated by Lovell et al. (2008), and replicates the physiological and mechanical demands of soccer match-play.
The protocol is based around a 20 meter shuttle run, with the incorporation of four positioned poles for the participants to navigate through using utility movements inherent to match-play
The movement intensity and activity performed is maintained using verbal signals on an MP3 audio file.
Adapted from Small et al. (2010)

6. 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
Half time
2nd half T0
45 mins
T45
15 mins
T60
T105
During the performance of the protocol; Heart rate responses were recorded at 15 minute intervals.
Isokinetic peak torque for the knee flexors and extensors was measured prior to protocol performance (T0), after the 1st half (T45), after half time (T60) and after the completion of the protocol (T105).
Assessments were done at isokinetic testing speeds of 60 and 180ᵒ.s-1, in both concentric and eccentric modalities.
And this was done In both the Dominant and non-dominant limbs
Subsequently, EccH and ConQ strength were used to calculate the functional strength ratio, which is used as a descriptor of knee function and to identifying potential muscle imbalances at the knee.

7. Results Heart Rate: 1st half 2nd half 162 (±13) bt.min-1
A mean heart rate of 162 bt.min-1 was observed during the 1st half, while a mean of 160 bt.min-1 was observed during the 2nd half. With No significant difference observed between the 2 halves.
As illustrated in the table: The HR responses elicited during the present study were found to be similar to those of match-play and other laboratory based studies.
Where: HR=Heart rate (Adapted from Lovell et al., 2008)

8. Results (cont.) Isokinetics: Eccentric Hamstrings PT
17.34% 
18.27% 
EccH peak torque was observed to decrease as a function of time at both isokinetic testing speeds.
At 60°.s-1, a significant 17.34% overall reduction was illustrated, with a significant decrease observed after both the first and second halves.
And at the faster isokinetic speed, a significant overall decrease of 18.27% was demonstrated, once again with a significant decrease observed after the first and second halves.
No significant effect of leg dominance was observed at either speed.
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

9. Results (cont.) Isokinetics: Functional strength ratio (eccH:conQ)
10.04% 
The functional strength ratio indicated no significant change overall at the slower isokinetic testing speed.
However, at 180°.s-1, a significant 10.04% overall decrease was observed. At this speed, a 4.35% (p>0.05) reduction occurred during the 1st half and a 12.10% (p<0.05) reduction was observed during the 2nd half.
No significant effect of leg dominance was observed at either speed.
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

10. 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
The SAFT90 exercise protocol was indicated to reduce the capacity of the hamstrings and quadriceps muscles to develop force.
The temporal changes in eccH strength and the H:Q ratio support epidemiological data, with hamstring injuries more likely to occur within the latter stages of both halves.
The decline in eccentric hamstring muscle strength is attributed to the eccentric loading that occurs as a result of the intermittent activity profile.
Where the constant accelerations, decelerations and changes in direction result in eccentric muscle fatigue
Therefore, the hamstrings have insufficient eccentric strength to decelerate the lower limb during sprinting, resulting in eccentric overload and damage to the muscle
And in the present study, the associated risk of hamstring injury is indicated to be the same in both the dominant and non-dominant legs.

11. 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) %  [Professional/European]
180°.s-1: 18.27%  in EccH PT in agreement with;
Greig (2008) % 
Greig and Siegler (2009) %  [Professional/European]
Values similar to those of numerous authors while at 120°.s-1;
Rahnama et al. (2003) %  [Amateur/European]
Small et al. (2010) %  [Semi-Prof/European]
Lovell et al. (2011) %  [Semi-Prof/European]
Comparisons between the available studies investigating soccer-specific muscular fatigue are difficult. The relevant studies vary significantly in the type of protocol used, isokinetic testing velocity and the competitive playing level of the participants.
The 17.34% decrease in eccH strength observed at 60°.s-1 is similar to the 18.10% reduction observed by Greig (2008) in professional European players, using the same testing speed.
At 180°.s-1 the 18.27% decrease is in agreement with Greig (2008) and Greig and Siegler (2009), who both observed an 18% decrease in cohorts of professional European players.
These values are similar to numerous authors who utilised a speed of 120°.s-1 in both amateur and semi-professional European players.
Rahnama et al. (2003) and Small et al. (2010) both observed a 16.8% decrease, while Lovell et al. (2011) observed a 20.65% decrease.

12. 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) % 
Similar decrements observed at 120°.s-1 in amateur and semi- professional Caucasian players;
Rahnama et al. (2003) %  [Amateur/European]
Small et al. (2010) %  [Semi-Prof/European]
With regards to the functional strength ratio; the slow isokinetic velocity indicated no significant overall effect of time, which is in agreement with Greig (2008)
But 180°.s-1, the significant 10.04% overall reduction is similar to Greig (2008) at the same isokinetic speed, although Greig (2008) observed a larger decrease.
Once again, authors using a isokinetic testing speed of 120°.s-1 in amateur and semi-professional European players observed similar reductions to the present study.
Rahnama et al. (2003) indicated a 12.99% decrease and Small et al. (2010) a 15% decrease.

13. 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
In conclusion, Eccentric hamstring peak torque, and subsequently the functional strength ratio, were indicated to deteriorate as a function of protocol duration.
Indicates that the hamstrings have insufficient eccentric strength to decelerate the lower leg during the late swing phase, particularly towards the latter stages of both halves of play.
These temporal changes have negative implications for performance and injury risk.
With regards to the Black African playing population, present research suggests that Black African amateur soccer players experience eccentric hamstring fatigue in a similar manner to Caucasian European soccer players. And are therefore exposed to a similar risk of hamstring strain injuries during match-play.
The observed changes in hamstring strength indicate that injury prevention strategies need to consider reducing the negative impacts of fatigue on hamstring function. A greater resistance to eccentric fatigue in the hamstrings will positively affect the functional strength ratio, reducing the associated risk of injury.
Thank you!

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15. rijones88@gmail.com Tel: +27 (0) 82 440 2771 Contact Details
Acknowledgements: Andrew Todd (supervisor)
Candice Christie (HoD)
CATHSSETA