Original research
Eccentric hamstring strength deficit and poor hamstring-to-quadriceps ratio are risk factors for hamstring strain injury in football: A prospective study of 146 professional players

https://doi.org/10.1016/j.jsams.2017.11.017Get rights and content

Abstract

Objectives

The purpose of this study was to investigate whether preseason isokinetic strength measures were predictive of future HSI among professional football players.

Design

Prospective cohort study, Level of evidence 2.

Methods

A total of 169 professional players participated in a preseason isokinetic strength screening, followed by a 10-month competitive season. Testing protocol included the concentric performance of both knee flexion and extension at 60 deg s−1 and 240 deg s−1 and the eccentric performance of the knee flexor at 30 deg s−1. Strength deficits, bilateral differences, and hamstring to quadriceps strength ratios were computed. Univariate and multivariate logistic regressions were used to identify potential risk factors of HSI. Receiver operating characteristic (ROC) curves were used to investigate the sensitivity and specificity of the strength measures.

Results

Forty-one acute HSIs were sustained, and 12% (n = 5) reoccurred within the study period. In the multivariate analysis, we have shown an association between the injury risk and eccentric hamstring peak torque below 2.4 N m kg−1 (OR = 5.59; 95% CI, 2.20–12.92); concentric H/Q ratio below 50.5% (OR = 3.14; 95% CI, 1.37–2.22); players with previous injury of HSI (OR = 3.57; 95% CI, 3.13–8.62). ROC analysis displayed an area under curve (AUC) of 0.77, indicating fair combined sensitivity and specificity of the overall predicting model.

Conclusions

Professional football players with significant lower isokinetic hamstring strength, lower hamstring-to-quadriceps strength ratio, and a previous injury of HSI were linked to an increased risk of acute HSI.

Introduction

Hamstring strain injuries (HSI) remain a significant concern in professional football, because of the amount of time away from the sport and a declined level of performance for the injured athlete. HSI represent 10–12% of overall injuries and more than one-third of all muscle injuries in elite soccer.1, 2 The injury incidence of HSI has increased over the past decade.3 The recurrence rates range from 12% to 41% during the first year of returning to play.4, 5, 6 Understanding the multifactorial risk factors and mechanisms of this injury are crucial for developing effective injury prevention measures.7, 8

The majority of the HSI in elite football players occur during high-speed running, which involves rapid eccentric hamstring muscle contraction.9, 10, 6 Intrinsic risk factors leading to an increased risk of HSI may be identified from previous studies. Such risk factors include previous injury of HSI,11, 12, 4, 13, 14, 15, 16 older age,14, 15, 17 reduced hamstring strength,17, 18 reduced quadriceps strength,19, 18 lower hamstring to quadriceps (H/Q) strength ratio,20, 21, 19, 22 bilateral difference in hamstring fascicle length,23 and bilateral difference in hamstring strength,17, 19 but results from different studies are conflicting. Variations in methodology and testing protocols compromise the comparison between published data in the literature, which may contribute to those contradicting results.21

A large prospective cohort study on professional football players has shown lower isokinetic eccentric hamstring strength at 60 deg s−1 (OR = 1.4; 95% CI, 1.0–1.9; p = 0.04) and lower concentric isokinetic quadriceps strength at 60 deg s−1 (OR = 1.4; 95% CI, 1.0–1.9; p = 0.04) as weak risk factors of HSI, while bilateral difference of hamstring strength measures were not.18 Croisier et al.21 suggested that a concentric H/Q ratio (Con 60/Con 60) lower than 0.55 is associated with injury risk of HSI (RR = 2.89, 95% CI, 1.0–8.3, p < 0.05). Fousekis et al.13 found that eccentric isokinetic hamstring strength asymmetries at 60 and 180 deg s−1 correlated with increased risk of HSI, while H/Q ratio (Ecc 180/Con 180) did not. A meta-analysis study suggested that hamstring peak torque and hamstring-to-quadriceps (H/Q) ratio require further research to warrant their involvement in HSI because of inconclusive results, or small sample sizes.14

Despite an ample amount of literature exploring the topic, the relationship between hamstring injuries and isokinetic strength deficits remains controversial. The primary aim of this study was to investigate whether preseason isokinetic strength measures were predictive of future HSI among professional football players. The secondary aim was to determine potential risk factors and their confounding factors that associated with increased risk of HSI.

Section snippets

Methods

The prospective cohort study was approved by the university clinical research ethics committee. The sample consisted 169 professional football players, who were from six teams of the top national football league. These teams had football training every day and 1–2 weekly official matches during the competitive season. Players who participate in the first-team training were invited and signed written informed consents.

Players participated in the isokinetic testing session during the pre-season

Results

Twenty-three players who were unable to complete the isokinetic strength test were excluded from this study. A total of 146 professional football players (age, 24.2 ± 4.4 years.; height, 177.7 ± 5.9 cm; weight, 72.9 ± 8.65 kg; playing experience, 4.53 ± 3.65 years.) participated in this cohort study. Forty-one hamstring injuries (23 Right and 18 Left) were recorded. Among the 41 hamstring injuries, 56% (n = 23) were on the dominant side, and 12% (n = 5) recurred within the study period. The average time lost

Discussion

The aim of this study was to investigate potential intrinsic risk factors for hamstring strain injuries among professional football players. The key finding of this cohort study was that a previous history of an acute hamstring injury, lower eccentric hamstring strength, and lower concentric hamstring to quadriceps strength ratio are significant risk factors of HSI. Previously injured players have a 3.6-fold higher risk of sustaining HSI. Players with a preseason eccentric hamstring peak torque

Conclusion

Professional football players with clinically significant lower isokinetic hamstring strength, lower H/Q ratio, and a previous injury of HSI were linked to increased risk of acute future HSI. Other potential risk factors, such as age, a bilateral difference of isokinetic hamstring strength measures, isokinetic quadriceps strength measures, height, and weight, proved to be irrelevant to the risk of HSI. A preseason screening of H/Q ratio (Con 60/Con 60), and eccentric hamstring strength (Ecc 30)

Practical implications

  • Players with history of previous hamstring strain injuries have a 3.6-fold higher risk of sustaining hamstring strain injuries.

  • Low speed hamstring-to-quadriceps strength ratio and eccentric hamstring strength are modifiable risk factors of hamstring strain injuries among professional football players.

  • It is recommended to test the isokinetic quadriceps and hamstring strength at slow speed, which is 30–60 deg s−1.

  • Team medical staffs may monitor players’ eccentric hamstring strength and

Acknowledgements

There has been no external financial assistance with this project.

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