Preventing Non-Contact Hamstring Injuries in Elite Footballers: Eccentric vs Concentric Training

Efficacy of Eccentric Over Concentric Hamstring Exercises in Elite Male Footballers for Preventing Non-Contact Hamstring Injuries: A Randomized Controlled Trial

Football is a sport with a high risk of injury, and hamstring muscle injuries are among the most common problems faced by players. These injuries can reduce a player's performance, cause time away from training and matches, and place a burden on medical teams and clubs. Many training programs recommend eccentric hamstring exercises to prevent these injuries, but there is limited evidence comparing eccentric exercises with concentric exercises or a combination of both, especially in elite male football players.

The purpose of this study is to compare the long-term effects of three different hamstring strengthening programs-eccentric training, concentric training, and a combination of both-on preventing non-contact hamstring injuries in elite male footballers. Each training program will last for three months, and the players will be followed for a total period of 12 months. The study will look at how these programs affect hamstring injury prevention, muscle strength and performance, flexibility, recurrence of injuries, and players' psychological satisfaction.

The study is based on the following expectations:

A three-month eccentric hamstring strengthening program will lead to long-term improvements in reducing hamstring injuries, improving muscle performance and flexibility, lowering injury recurrence, and increasing psychological satisfaction over a 12-month period.

A three-month concentric hamstring strengthening program will also result in long-term improvements in injury prevention, muscle performance, flexibility, injury recurrence, and psychological satisfaction.

A combined program of eccentric and concentric hamstring strengthening over three months will produce significant long-term benefits in injury prevention, muscle performance, flexibility, injury recurrence, and psychological satisfaction.

There will be clear differences in outcomes between the eccentric, concentric, combined, and control groups over the 12-month follow-up period.

Participants will be divided into four groups (A, B, C, and D) based on the type of training they receive. The study will include young male professional football players aged 18 to 30 years from the UAE who are citizens or permanent residents. All participants must speak English, have at least one year of football playing experience, and must not have had any hamstring injury in the past six months. Players who are interested in participating and provide written informed consent will be included.

Players will be excluded if they have had a hamstring injury in the last six months, are female, are under 18 or over 30 years old, have restrictions in knee movement, have undergone previous hamstring surgery, are currently enrolled in another official rehabilitation program, or do not agree to participate in the study.

Group A participants will perform eccentric hamstring exercises, including Nordic hamstring curls, dumbbell stiff-leg deadlifts, and barbell Romanian deadlifts. Group B participants will perform concentric hamstring exercises such as seated leg curls, lying leg curls, and prone hamstring curls using resistance bands. Group C participants will perform a combination of both eccentric and concentric hamstring exercises. Group D participants will continue with their usual football training only and will not perform any additional hamstring-specific exercises.

Before each training session, all participants in Groups A, B, and C will complete a 10-minute warm-up, consisting of five minutes of cycling, three minutes of stretching, and two minutes of rope jumping. Each training session will last at least 30 minutes. The exercise groups will complete three additional training sessions per week alongside their regular football training for a total of 12 weeks.

The results of this study will help determine which type of hamstring training program is most effective in preventing non-contact hamstring injuries and improving physical and psychological outcomes in elite male football players.

Background and Rationale Football is associated with one of the highest injury rates among competitive sports, with hamstring muscle injuries representing a major cause of time loss, reduced performance, and increased medical burden. Epidemiological evidence indicates that approximately 80% of hamstring injuries in football occur without direct contact, most commonly during high-speed running, sprinting, acceleration, deceleration, and sudden changes of direction. These injuries are associated with high recurrence rates and may significantly impact player availability and long-term athletic performance.

Hamstring muscle function plays a critical role in knee and hip stability, particularly during the terminal swing phase of sprinting when the hamstrings are subjected to high eccentric loads. Muscle weakness, fatigue, reduced flexibility, and imbalances between concentric and eccentric strength have been identified as key intrinsic risk factors for hamstring strain injuries in footballers.

Eccentric hamstring strengthening exercises-such as the Nordic hamstring exercise-are widely advocated for injury prevention due to their ability to increase muscle strength, fascicle length, and neuromuscular control. However, emerging evidence suggests that concentric strengthening and combined eccentric-concentric programs may also contribute to improved muscle performance and fatigue resistance. Despite extensive research on eccentric training, direct comparisons between eccentric, concentric, and combined hamstring strengthening programs in elite male football players remain limited, particularly with long-term follow-up across an entire competitive season.

Therefore, this randomized controlled trial aims to systematically evaluate and compare the long-term effectiveness of eccentric, concentric, and combined hamstring strengthening programs in preventing non-contact hamstring injuries, improving muscle performance and flexibility, reducing injury recurrence, and enhancing psychological satisfaction in elite male footballers.

Aim of the Study To compare the long-term effects of eccentric, concentric, and combined hamstring strengthening programs-each conducted over a three-month intervention period-on non-contact hamstring injury prevention, muscle performance, flexibility, injury recurrence, and psychological satisfaction in elite male football players over a 12-month follow-up period.

Specific Objectives

1. To evaluate changes in the incidence of non-contact hamstring injuries following eccentric, concentric, and combined hamstring strengthening programs.
2. To assess improvements in hamstring muscle performance and flexibility in response to different strengthening protocols.
3. To determine the recurrence rate of hamstring injuries during the 12-month follow-up period.
4. To assess psychological satisfaction and perceived sports performance among players undergoing each intervention.
5. To identify the most effective hamstring strengthening approach for injury prevention and performance enhancement in elite male footballers.

Hypotheses

1. A three-month eccentric hamstring strengthening program will produce significant long-term improvements in injury prevention, muscle performance, flexibility, reduced recurrence rates, and psychological satisfaction over a 12-month period.
2. A three-month concentric hamstring strengthening program will result in significant long-term improvements in the same outcome measures.
3. A combined eccentric and concentric hamstring strengthening program will yield significant long-term benefits across all outcome measures.
4. Significant differences will exist among eccentric, concentric, combined, and control groups with respect to injury incidence, muscle performance, flexibility, recurrence rates, and psychological satisfaction over the 12-month follow-up period.

Study Design This study is designed as a single-blind randomized controlled trial conducted over a 12-month period. Eligible participants will be randomly allocated into four intervention groups.

Study Setting The study will be conducted in collaboration with selected elite football clubs across the United Arab Emirates. All exercise interventions and injury management will be supervised by qualified physiotherapists at the Physiotherapy and Sports Medicine Center, Ras Al Khaimah.

Randomization and Blinding Randomization will be performed using an automated system by an independent individual not involved in the study. Participants will be allocated sequentially into one of four groups to ensure balanced distribution. Due to the nature of the interventions, the study will follow an open-label design; however, outcome assessors will remain blinded to group allocation to reduce assessment bias.

Intervention Groups Group A: Eccentric Training + Regular Football Training

Participants will perform:

• Nordic hamstring curls
• Dumbbell stiff-leg deadlifts
• Barbell Romanian deadlifts Group B: Concentric Training + Regular Football Training

Participants will perform:

• Seated leg curls
• Lying leg curls
• Prone hamstring curls with resistance bands Group C: Combined Eccentric and Concentric Training + Regular Football Training Participants will perform all exercises listed in Groups A and B. Group D: Control Group Participants will continue with regular football training only, without additional hamstring-specific exercises.

Training Protocol

• Frequency: 3 sessions per week

• Duration: Minimum of 30 minutes per session

• Intervention period: 12 weeks

• Warm-up (10 minutes):

  • 5 minutes cycling
  • 3 minutes stretching
  • 2 minutes rope jumping All sessions will be supervised to ensure safety and adherence. Outcome Measures Primary Outcome

• Incidence of non-contact hamstring injuries Secondary Outcomes

• Hamstring flexibility (Sit-and-Reach Test, Active Knee Extension Test)

• Muscle performance (30-meter sprint time, vertical jump height)

• Injury recurrence rates

• Psychological satisfaction (Subjective Sports Performance Satisfaction Questionnaire) Assessments will be conducted at baseline, post-intervention (3 months), and at 6, 9, and 12 months.

Safety and Risk Management All interventions will be supervised by trained professionals. Participants will be monitored for adverse events, including muscle soreness, strain, or joint discomfort. Pain levels will be recorded using the Visual Analogue Scale, and thigh circumference will be measured to detect swelling. Immediate medical care will be provided if required.

Ethical Considerations Participation is voluntary, and players may withdraw at any time without penalty. Written informed consent will be obtained prior to participation. Confidentiality will be maintained through anonymized data storage and restricted access. Ethical approval will be obtained from relevant institutional and national ethics committees prior to study commencement.

Expected Outcomes It is anticipated that eccentric hamstring strengthening will demonstrate superior effectiveness in reducing non-contact hamstring injuries, improving flexibility, enhancing sprint performance, and increasing psychological satisfaction compared to concentric or combined programs. The findings are expected to inform evidence-based injury prevention strategies in elite football.

Dissemination of Results

Results will be disseminated through:

• PhD thesis submission
• Publication in Scopus-indexed journals
• National and international conferences
• Reports shared with participating clubs and sports authorities Project Duration Total duration: 12 months, including baseline assessment, intervention phase, follow-up assessments, and data analysis.

Inclusion Criteria:

• Players without any recent hamstring injuries (within the last 6 months) from certain clubs will be asked to join the trial.
• The trial will include young male professional football players aged 18-30 from the UAE who are citizens or permanent residents, English speaking, with no hamstring injuries in the last six months.
• Participants must have at least one year of experience playing football and be interested in participating in the study.

Exclusion Criteria:

• Players who have had hamstring injuries within the last 6 months, women, individuals under 18 and over 30 years old will be disqualified.
• Individuals who have any restrictions in exercising the knee, have undergone prior surgery on their hamstring, or decline to give written informed consent for the study are not eligible.
• Furthermore, we will not include player who are currently enrolled in other official rehabilitation programs.