[Gilson Sampaio Pereira is a master’s student at University of Stuttgart, Germany, and Sport Performance Coach. He is currently in the Coaching Mentorship Program at Athletic Lab] 

In this blog post I will present a simple and cost effective method of assessing concentric and eccentric strength/power during hip extension. Lower limb asymmetries can also be assessed in the same test. The test is a hip extension exercise, with a flywheel device (FD) to generate an eccentric overload. The FD is gaining popularity on the S&C and athletic development scene because it exposes athletes to high loads with minimum equipment. Additionally, there might be superior gains in strength, power and hypertrophy with flywheel training due to an eccentric overload, when compared to traditional resistance training (Maroto-Izquierdo et al., 2017).

First, a little background

Let´s begin by stepping into the literature to better understand why testing hip extension strength could be of value to athletes and coaches.  Hip extension is a basic functional movement. The major hip extensors are the spinal erectors, gluteus maximus, biceps femoris (long head), semitendinosus, semimembranosus and adductor magnus.

First, compared to knee extension, hip extension is more important in running speed (Schache et al., 2011), jump height (Lees et al. 2004) and back squat (Bryanton et al. 2011). Therefore, the role of hip extension becomes more significant when athletic movements are executed with a high intent. As a logical consequence, a sound S&C coach should favor the development of the hip extensors in their preparation and maintenance phases throughout the year. This was backed up by a study from Contreras et al. (2016) that showed a greater effect of horizontally than vertically loaded hip extension training on sprint acceleration (e.g. hip thrusters).

Second, the research shows a preventive role of strong and powerful hip extensors. Lack of hip extension strength has been associated with knee pain in the symptomatic leg in females (Rowe et al., 2007). Further, looking at a study done over three consecutive seasons identified reduced hip extension strength as a risk factor for lateral ankle sprains in male youth soccer players (Ridder et al., 2017). Therefore, an asymmetry between legs could also be an indicator of future lower limb dysfunctions, or crucial in the evaluation of return to play after injury rehabilitation.
Looking now at the pinnacle of injury prevention in sports involving high speed sprinting – hamstring injuries – Bourne et al. (2016) found distinct activation patterns of the hamstrings during yielding phases of hip extension (45° Back extension) and knee flexion (Nordic Hamstring Exercise). This should implicate the assessment of both movements to ensure functional integrity of the different parts of the hamstrings for potential injury prevention. In addition to that Fousekis et al. (2011) evaluated risk factors for muscle strains in hamstrings and quadriceps. They found that eccentric strength asymmetries between legs increased the likelihood for muscle strains. Coaches should therefore be aware of it. Even though there is no strict guidelines for asymmetry, Dr. Matt Jordan said on the HPAD 2017 conference to avoid asymmetries exceeding 15-20% between legs.

Third, Ford et al. (2013) found a relationship between hip extension strength (+ abduction strength) and trunk rotation movement, as well as excessive dropping of the hip in the frontal plane while running. In other words, stronger hip extensors might improve postural control of the hip and upper body. The study was conducted at moderate running speeds (Speed: 25 seconds on a 100m dash) in collegiate cross-country runners and might have some importance for team sport athletes during transition phases in the game.

Testing hip extension power and limb asymmetries with the flywheel device

Most of the research is done using expensive equipment that cost from tens to hundreds of thousands of dollars (it´s worth it in terms of highly accurate measurement).  Tests are done with either isometric contractions by applying force to a fixed object, or isokinetic contractions by applying force to an object moving at a constant speed. Alternatively, and at a fraction of the cost, a flywheel device uses an isoinertial load that is fixed by the diameter of the flywheel. It´s accelerated in the concentric phase via a cord that attaches to an axis and effort from the user. By that, raising the spinning velocity of the flywheel, the inertia raises too. At a preselected end range of the cord the spinning wheel reels it back in, which forces the user to resist the built up inertia. In this breaking phase the user can create an eccentric overload by trying to reverse the pulling motion with maximal intent. By using the FD eccentric power output can exceed concentric power output like in sprinting and jumping. The harder you concentrically accelerate, the harder it reverses. Another interesting fact is the use of a stretch shortening cycle (SSC) movement (explained elsewhere by Komi, 2003, p. 184-202). When decelerating the flywheel the muscle-tendon-complexes of the hip extensors are stretched under load which might lead to a storage of elastic energy and preload the consecutive concentric phase. The biggest difference to the traditional methods mentioned above is the measurement of force and power in the coupled eccentric–concentric motion. This might be more specific to actual athletic movements, which mostly occur in that fashion (Komi, 2003, p. 184).

Digging deeper with a self-assessment

I conducted a study on myself using the “Exxentric kBox4 + kMeter,” and a standard Glute-Ham-Raise. The hip extension used for the test was a bilateral and unilateral hyperextension with the inertia of the flywheel at 0.025 kgm2, and 0.010 kgm2, respectively.

The kMeter shows concentric and eccentric peak and average power, as well as force. If the data is exported to an excel sheet there is the possibility to evaluate every repetition into more detailed parameters. In addition, it provides the relative eccentric overload. The higher the number the better the ability to absorb high forces which, for example, can be an indicator for horizontal force production (Morin, 2015). In my case, the eccentric overload in the bi-lateral hip-extension was 12%. After assessing each leg at a time there was a big difference in peak power output between both legs.

Interestingly, there was a bigger eccentric than concentric peak power discrepancy (46% ecc. vs. 21% con.) between legs. That means my weaker leg was able to absorb less force compared to the stronger leg. It is of interest that the knee in the weaker leg was bothering me for a year and a half up until six months ago. That may be the reason for an ongoing inhibition which I didn’t notice, but could increase the likelihood of injury.

Final thoughts

To gather stronger scientific evidence for this method there a study with a more subjects must be done. However, if testing and monitoring athletes outside of well equipped sports science lab, this method could offer coaches some useful data to spot big differences in limb power production. More importantly, it can serve to test eccentric power. S&C-Coaches can evaluate training programs as well as provide more information in return-to-play scenarios during preparation phases and in-season. In team sports training and monitoring it´s also all about efficiency – the FD represents a multifunctional training device with additional data provision. It can be used as a testing and training device at the same time while consuming little time in assessing multiple athletes, and at a much lower cost than more common equipment found in a lab.

I hope this novel assessment method offers valuable insight for coaches. At the end of the day it can be very useful to present data driven programs to the manager and sports medicine staff as well as strengthen the position of the S&C-Coach.

References

Bourne, M.N., Williams, M.D., Opar, D.A., Al Najjar, A., Kerr, G.K. & Shield, A.J. (2016). Impact of exercise selection on hamstring muscle activation. British journal of sports medicine, 51, 1021-1028.

Bryanton, M. A., Kennedy, M. D., Carey, J. P., & Chiu, L. Z. (2012). Effect of Squat Depth and Barbell Load on Relative Muscular Effort in Squatting. The Journal of Strength & Conditioning Research, 26(10), 2820-8.

Contreras, B., Vigotsky, A. D., Schoenfeld, B. J., Beardsley, C., McMaster, D. T., Reyneke, J., & Cronin, J. (2016). Effects of a six-week hip thrust versus front squat resistance training program on performance in adolescent males: A randomized-controlled trial. The Journal of Strength & Conditioning Research, 31(4), 999-1008.

Ford, K.R., Taylor-Haas, J.A., Genthe, K. & Hugentobler, J. (2013). Relationship between hip strength and trunk motion in college cross-country runners. Medicine and science in sports and exercise, 45 (6), 1125–1130.

Fousekis, K., Tsepis, E., Poulmedis, P., Athanasopoulos, S. & Vagenas, G. (2011). Intrinsic risk factors of non-contact quadriceps and hamstring strains in soccer: a prospective study of 100 professional players. British journal of sports medicine, 45 (9), 709–714.

Komi, P.V. (2003). Stretch-Shortening Cycle. In P.V. Komi (Hrsg.), Strength and power in sport (The Encyclopaedia of sports medicine, v. 3, S. 184–202). Osney Mead, Oxford, Malden, MA: Blackwell Science.

Lees, A., Vanrenterghem, J., & De Clercq, D. (2004). The maximal and submaximal vertical jump: implications for strength and conditioning. The Journal of Strength & Conditioning Research, 18(4), 787-791.

Maroto-Izquierdo, S., García-López, D., Fernandez-Gonzalo, R., Moreira, O.C., González-Gallego, J., & de Paz, J.A. (2017). Skeletal muscle functional and structural adaptations after eccentric overload flywheel resistance training: a systematic review and meta-analysis. Journal of Science and Medicine in Sport.

Morin, J.-B., Gimenez, P., Edouard, P., Arnal, P., Jiménez-Reyes, P., Samozino, P., Mendiguchia, J. (2015). Sprint Acceleration Mechanics: The Major Role of Hamstrings in Horizontal Force Production. Frontiers in Physiology, 6, 404.

Ridder, R. de, Witvrouw, E., Dolphens, M., Roosen, P. & van Ginckel, A. (2017). Hip Strength as an Intrinsic Risk Factor for Lateral Ankle Sprains in Youth Soccer Players: A 3-Season Prospective Study. The American journal of sports medicine, 45 (2), 410–416.

Rowe, J., Shafer, L., Kelley, K., West, N., Dunning, T., Smith, R., & Mattson, D. J. (2007). Hip strength and knee pain in females. North American Journal of Sports Physical Therapy: NAJSPT, 2(3), 164.

Schache, A. G., Blanch, P. D., Dorn, T. W., Brown, N. A., Rosemond, D., & Pandy, M. G. (2011). Effect of running speed on lower limb joint kinetics. Medicine and science in sports and exercise, 43(7), 1260.