Hamstring injuries are one of the common injuries in running based sports and can often lead to considerable time loss from both training and competition. For instance, hamstring strain injury is the most common non-contact injury, representing 37% of all muscle traumas in professional sport (Oleksy et.al. 2021).  

During dynamic movements such as running, jumping, and changes of direction, the hamstring muscles undergo rapid lengthening (eccentric contraction) followed immediately by shortening (concentric contraction), placing considerable stress on the muscle–tendon unit. This rapid sequence is referred to as the stretch–shortening cycle (SSC).  

Training methods that emphasize eccentric loading have been shown to be an effective preventive plan. Plyometrics and eccentric strength training exercises such as Nordic curls can enhance SSC efficiency, while flywheel resistance training (FRT) offers considerable benefits by providing consistent tension, continuous motion and eccentric resistance. Nordics may reduce injury rates through positive muscle architectural changes, though questions remain about optimal loading and varying body positions.

Nordic curls

Nordic curls emphasize eccentric control of the hamstrings (resisting lengthening), which directly mimics the hamstring’s role during sprinting, especially the late swing phase where most hamstring strains occur. The exercise increases biceps femoris fascicle length and eccentric torque, both linked to lower risk of strain.

Multiple studies (Petersen et al., 2011; van Dyk et al., 2019) show that incorporating Nordic curls into training reduces hamstring injury rates in soccer, rugby, and sprint athletes.

• While great for prevention, they don’t train the hamstrings in all roles (hip extension strength, sprint mechanics, or end-range flexibility).

• If introduced too soon after injury Nordic curls can place high tensile load at long muscle lengths—which can aggravate healing tissue.

• Also, if athletes aren’t accustomed, Nordics can cause intense soreness and short-term stiffness, which may increase re-injury risk if not managed.

• Fixed resistance: once you control your bodyweight, progression options are very limited (although athletes can add weighted vest or exercise bands).

• Primarily knee-dominant, less hip-extensor emphasis.

Flywheel Resistance Training (e.g., RDLs, leg curls, hip extensions)

The muscle-lengthening stimulus promotes greater strength development, neuromuscular control, and tendon adaptation. Such adaptations are critical for both performance and injury prevention, as they reduce the risk of hamstring strains and improve the ability to perform high-intensity actions that depend heavily on the SSC, including sprinting, cutting, and explosive field or court movements.

Multiple studies (Hu et al., 2024; Martinez-Hernandez 2023; Gonzalo-Skok et al., 2017) show that incorporating flywheel training into an athlete’s strength program improves the muscles’ explosive strength, neuromuscular functions, and improves the athlete’s running economy.

• Athlete controls concentric effort; the flywheel “pulls back” eccentrically, allowing eccentric overload (harder lowering than lifting).

• Allows progressive eccentric loading at both hip-dominant (RDL, hip hinge) and knee-dominant (leg curl) positions.

• Trains the hamstrings in sprinting-relevant actions (hip extension under load, coordination at different joint angles).

• Greater power output potential → better sprint transfer.

• Advanced eccentric overload with Exerfly’s motorized technology. The technology enhances eccentric overload up to 80%, adjusting in real time based on the concentric force. For example, if set to a 20% boost, the eccentric phase gains 20% more energy than during the concentric phase.

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Nordic Curl vs Flywheel Training

Summary

Both Nordic curls and flywheel training exercises emphasize eccentric muscle contractions but differ in scope, adaptability, and overall application. Flywheel training provides a broader multi-purpose, full-body eccentric overload and is superior to overall athlete performance and rehab prevention. Flywheel and nordic curls do complement one another—nordics for targeted posterior chain work, flywheel resistance training for global eccentric and concentric development during hip dominant and knee dominant exercises.

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References

Oleksy, L., Mika, A., Pacana, J., Markowska, O.,  Stolarczyk, A. and Kielnar, R. (2021) Why Is Hamstring Strain Injury so Common in Sport Despite Numerous Prevention Methods? Are There Any Missing Pieces to This Puzzle? Frontiers in Physiology. 12: 1-3.

Petersen, J., Thorborg, K. &  Holmich, P. (2011) Preventive Effect of Eccentric Training on Acute Hamstring Injuries in Men’s Soccer: A Cluster-Randomized Controlled Trial. The American Jnl of Sports Medicine. 39(11).  

van Dyk, N., Behan, F.P. & Whiteley, R. (2019) Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: a systematic review and meta-analysis of 8459 athletes. British Jnl of Sports Medicine. 53: 1362-1370.

Hu, Z., Liu, Y., Huang, K., Huang, H., Zhang, Y. and Yuan, X. (2024) Effects of Inertial Flywheel Training vs. Accentuated Eccentric Loading Training on Strength, Power, and Speed in Well-Trained Male College Sprinters. Life 14, 1081 1-16.

Martinez-Hernandez, D. (2023) Flywheel Eccentric Training: How to Effectively Generate Eccentric Overload. Strength & Conditioning Journal. 1-17.

Gonzalo-Skok, O., Tous-Fajardo, J., Valero-Campo, C., Berzosa, C., Bataller, A.V., Arjol-Serrano, J.L., Moras, G. & Mendez-Villanueva, A. (2017) Eccentric-Overload Training in Team Sport Functional Performance: A constant bilateral vertical versus variable unilateral multidirectional movements. International Jnl Sports Physio Perform. 12(7): 951-958.