Share this article on:

lncreasing Role of Hips Supported by Electromyography and Musculoskeletal Modeling

Beardsley, Chris BA (Hons), MA (Hons)1; Contreras, Bret BSc2

Strength & Conditioning Journal: August 2014 - Volume 36 - Issue 4 - p 100–101
doi: 10.1519/SSC.0000000000000081
Letter to the Editor

1Strength and Conditioning Research Limited, Loughborough, Leicestershire, United Kingdom; and

2School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand

Conflicts of Interest and Source of Funding: The authors report no conflicts of interest and no source of funding.

Chris Beardsley is the Director of Strength and Conditioning Research Limited.

Bret Contreras is currently pursuing his PhD at AUT University.

Back to Top | Article Outline


We thank Bryanton and Chiu (4) for their interest in our article (2). We are pleased that they consider our proposal interesting and note their concerns regarding the dangers of simplifying complex biomechanics. Nevertheless, since Strength and Conditioning Journal is primarily aimed at practitioners and not academics, simplification of complex terminology is warranted. Moreover, we do not feel our simplifications detract from the proposal as significantly as Bryanton and Chiu (4) suggest. Therefore, we stand by our conclusions and address their points one by one.

First, we consider our definition of joint moment to be correct and consistent with definitions found elsewhere in the literature (8). However, we agree that we should have spent more time covering the concepts of muscle cocontraction and proximal-to-distal sequencing, as well as precisely how the definition of joint moment relates to net joint moment (NJM) calculations.

Second, although we agree that knee extensor effort is underestimated in NJM calculations because of cocontraction, we note that hip extensor effort is also underestimated when accompanied by hip flexor cocontraction. Since the rectus femoris is both hip flexor and knee extensor, this point is particularly relevant during combined hip and knee extension movements. Moreover, the same issue can be found in any NJM calculation, including ankle plantar flexion, knee extension, hip extension, and lumbar extension. Each NJM will be underestimated in dynamic movement because of antagonist cocontraction. Indeed, almost all methods used in biomechanics possess inherent limitations, which is why it is helpful to consider the findings of different techniques. This is illustrated by the next point.

Third, we disagree that “greater hip extensor NJM must be accompanied by greater quadriceps efforts.” Electromyography (EMG) investigations have found that muscle activation increases to a greater extent in the hamstrings and gluteus maximus than in the quadriceps with increasing speed during running (3,6) and with increasing load during back squats (1,7). Similarly, musculoskeletal modeling shows that the muscle forces of the hamstrings and gluteus maximus increase to a much greater extent than those of the quadriceps with increasing running speed (5). Thus, both EMG and musculoskeletal modeling studies consistently support our proposal based on NJM data that ratios of hip extensor-to-knee extensor effort are altered with increasing load and speed in favor of the hip extensors.

Fourth, in addition to our point above, we consider the statement “strong quadriceps are required to achieve a large hip extensor NJM” too broad to encompass all movements. Some hip extension movements, including those that involve completely straight legs (e.g., back extensions) or semistraight legs (e.g., good mornings) will clearly not require as strong cocontractions from the knee extensors as those involving bent legs (e.g., squats).

Fifth, we believe that Bryanton and Chiu (4) are incorrect to infer that the hamstrings contribute 50% of the hip extensor strength during running and jumping on the basis of Waters et al. (11). First, Waters et al. state that “the hamstrings were found to account for about one-third of total hip extensor strength” (11), which is much less than 50%. Second, this study reported isometric and not dynamic strength. Third, Waters et al. assumed that only a small portion of the adductor magnus was innervated by the sciatic nerve. However, the majority of the adductor magnus is innervated by the sciatic nerve (10) and the entire muscle acts as a hip extensor at >16° of hip flexion (7), implying these calculations may underestimate adductor magnus contribution and overestimate hamstrings contribution. Fourth, the contribution of the hamstrings varied according to hip and knee flexion angles. Fifth, Waters et al. assumed that the moment arms of the hamstring and adductor magnus are similar, but this has since been found to be incorrect (7). It is impossible to ascertain the individual contributions of the hip extensors to hip extension strength as Bryanton and Chiu (4) propose, without establishing other data, including muscle lengths, muscle moment arm lengths, and muscle activation.

In conclusion, we consider the concerns presented by Bryanton and Chiu (4) to be misplaced, and we suggest that other areas of biomechanical research strongly support our proposal rather than undermine it. We maintain that although strengthening the knee extensors is important for enhancing sports performance, developing the hip extensors is paramount.

Back to Top | Article Outline


1. Aspe RR, Swinton PA. Electromyographic and kinetic comparison of the back squat and overhead squat biomechanical comparison of squatting exercises. J Strength Cond Res 2014. Epub ahead of print.
2. Beardsley C, Contreras B. The increasing role of the hip extensor musculature with heavier compound lower-body movements and more explosive sport actions. Strength Cond J 36: 49–55, 2014.
3. Belli A, Kyrolainen H, Komi PV. Moment and power of lower limb joints in running. J Sports Med 23: 136–141, 2002.
4. Bryanton MA, Chiu LZF. Hip- versus knee dominant task categorization oversimplifies multijoint dynamics. Strength Cond J. 98–99.
5. Dorn TW, Schache AG, Pandy MG. Muscular strategy shift in human running: Dependence of running speed on hip and ankle muscle performance. J Exp Biol 215: 1944–1956, 2012.
6. Kyröläinen H, Komi PV, Belli A. Changes in muscle activity patterns and kinetics with increasing running speed. J Strength Cond Res 13: 400–406, 1999.
7. Németh G, Ohlsén H. In vivo moment arm lengths for hip extensor muscles at different angles of hip flexion. J Biomech 18: 129–140, 1985.
8. Payne RC, Crompton RH, Isler K, Savage R, Vereecke EE, Günther MM, Thorpe KS, D'Août K. Morphological analysis of the hindlimb in apes and humans. II. Moment arms. J Anat 208: 725–742, 2006.
9. Paoli A, Marcolin G, Petrone N. The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. J Strength Cond 23: 246–250, 2009.
    10. Takizawa M, Suzuki D, Ito H, Fujimiya M, Uchiyama E. The adductor part of the adductor magnus is innervated by both obturator and sciatic nerves. Clin Anat 27: 778–782, 2014.
    11. Waters RL, Perry J, McDaniels JM, House K. The relative strength of the hamstrings during hip extension. J Bone Joint Surg Am 56: 1592–1597, 1974.
    © 2014 by the National Strength & Conditioning Association