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Relative Muscle Contributions to Net Joint Moments in the Barbell Back Squat

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Conference Paper

Relative Muscle Contributions to Net Joint Moments in the Barbell Back Squat

40th Annual Meeting of the American Society of Biomechanics, Raleigh, NC, USA, August 2nd – 5th, 2016
RELATIVE MUSCLE CONTRIBUTIONS TO NET JOINT MOMENTS IN THE
BARBELL BACK SQUAT
1,2 Andrew D. Vigotsky and 3 Megan A. Bryanton
1 Hospital for Special Surgery, New York, NY, USA
2 Arizona State University, Phoenix, AZ, USA
3 University of Ottawa, Ottawa, Ontario, Canada
email: avigotsky@gmail.com
INTRODUCTION
While the kinetics and kinematics of the back squat
have been well documented [1], in addition to
relative muscular efforts at the hip, knee, and ankle
joints [2], only one study has examined the
individual contributions of the monoarticular and
biarticular hip extensors, and how either strategy
may impact knee extensor efforts [3]; however,
individual muscle contributions to hip and knee
extension has not been thoroughly investigated.
This information would help strength and
conditioning professionals develop more effective
programming, in addition to proper technique
instruction, for developing maximal strength in
athletes. The purpose of this model was to evaluate
alterations in individual muscle contributions to hip
and knee extension with respect to barbell loading
and depth in the back squat exercise.
METHODS
Kinematic and kinetic data from ten resistance-
trained women were obtained from Bryanton, et al.
[2], wherein participants performed squats using 50
and 90% of their one repetition maximum (RM).
Parameters for the model included joint angles and
net moments as a function of squat depth (i.e., knee
angle), in addition to subject height and mass.
Using data from Handsfield, et al. [4], Hawkins, et
al. [5], Herzog, et al. [6], Nemeth [7], and Delp, et
al. [8], a musculoskeletal model was constructed in
MATLAB (MathWorks, Natick, MA) to estimate
subject-specific muscle sizes and moment arms. An
optimization algorithm then estimated muscle
moment contributions (gluteus maximus, adductor
magnus, biceps femoris, semitendinosus,
semimembranosus, rectus femoris, v. lateralis, v.
medialis, v. intermedius, medial gastrocnemius,
lateral gastrocnemius, and soleus) to yield the
necessary net joint moments, while minimizing the
sum of squared activations [9].
The passive and active contributions of each muscle
were modeled in accordance with their respective
length-tension curve. Relative moment
contributions of the hip and knee extensors were
calculated by dividing each muscle’s moment
contribution by the net joint moment of the joint in
question.
RESULTS AND DISCUSSION
The adductor magnus appears to play a pivotal role
in hip extension during the squat, producing, on
average, more than 50% of the net hip extension
moment (Figure 1). Particularly, this role is most
apparent in positions of greater squat depth and with
lighter loads. This is likely due to its larger hip
extension moment arm in positions of greater hip
flexion [7].
In higher squat positions, the gluteus maximus has
similar contributions as the adductor magnus in
generating a hip extension moment (Figure 1).
However, the decreasing moment arm with
increasing depth does not allow the gluteus
maximus to generate large hip extension moments
in deep flexion, despite it being in stretch [8].
Interestingly, the relative moment contributions of
the gluteus maximus do not appear to differ
substantially between 50 and 90% 1RM; the gluteus
40th Annual Meeting of the American Society of Biomechanics, Raleigh, NC, USA, August 2nd – 5th, 2016
maximus contributes relatively less in greater
degrees in hip flexion at both loads (Figure 1).
The hamstrings and adductor magnus appear to play
a complementary role in hip extension; if the
adductor magnus cannot produce a larger hip
extension moment with increased load, the
hamstrings increase their relative contribution in
order to compensate (Figure 1).
Figure 1. Relative muscle contributions to hip extension
during the squat with respect to depth and barbell load.
Hamstrings represent the sum of the biceps femoris,
semitendinosus, and semimembranosus.
The increasing role of the hamstrings at the hip with
greater barbell loading has implications for the
quadriceps, in that a greater hip extension moment
produced by the hamstrings necessarily means a
greater knee flexion moment. This increased knee
flexion moment must be countered by the
quadriceps in order to produce a sufficient net knee
extension moment [3] (Figure 2).
Although seemingly paradoxical, the rectus femoris
does not appear to contribute to the knee extension
moment in the squat (Figure 2). This is likely due to
its biarticular nature, in that the hip extensors may
not be able to produce a large enough moment to
overcome both the external and internal hip flexion
joint moments. Although the rectus femoris seems
to be highly active during the back squat in
electromyography studies [10], this may be a red
herring, as the rectus femoris is highly susceptible
to crosstalk from the vastii [11]. This is supported
by Fonseca et al [12] who found that the vastii, but
not the rectus femoris, hypertrophied following a
back squat-only program [12].
Figure 2. Relative muscle contributions to knee
extension during the squat with respect to depth and
barbell load. Vastii represent the sum of the v. lateralis,
v. medialis, and v. intermedis.
CONCLUSION
This work builds upon previous work by Bryanton,
et al. [3], by modeling the exact relative moment
contribution of each major muscle involved rather
than simply identifying a hip extension strategy. In
turn, it appears that the respective role of each
muscle during the back squat will vary as a function
of squat depth and barbell load.
REFERENCES
!
1. Escamilla, et al., Med. Sci. Sports Exerc. 33(6),
984-98, 2001.
2. Bryanton, et al., J. Strength Cond. Res. 26(10),
2820-8, 2012.
3. Bryanton, et al., Sports Biomech. 14(1), 122-38,
2015.
4. Handsfield, et al., J. Biomech. 47(3), 631-8, 2014.
5. Hawkins, et al., J. Biomech. 23(5), 487-494, 1989.
6. Herzog, et al., J. Anat. 182 ( Pt 2) 213-30, 1993.
7. Nemeth, Scand. J. Rehabil. Med. Suppl. 10 1-35,
1984.
8. Delp, et al., IEEE Trans. Biomed. Eng. 37(8), 757-
67, 1990.
9. Pedotti, et al., Math. Biosci. 38(1–2), 57-76, 1978.
10. Gorsuch, et al., J. Strength Cond. Res. 27(9),
2619-2625, 2013.
11. Byrne, et al., J. Electromyogr. Kinesiol. 15(6),
564-75, 2005.
12. Fonseca, et al., J. Strength Cond. Res. 28(11),
3085-92, 2014.
!
Adductor Magnus (90%)
Adductor Magnus (50%)
Gluteus Maximus (90%)
Gluteus Maximus (50%)
Hamstrings (90%)
Hamstrings (50%)
Relative hip extension moment contribution
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Knee flexion angle (º)
20 40 60 80 100
Vastii (90%)
Vastii (50%)
Rectus Femoris (90%)
Rectus Femoris (50%)
Hamstrings (90%)
Hamstrings (50%)
Relative knee extension moment contribution
1.0
0.5
0
0.5
1.0
1.5
2.0
Knee flexion angle (º)
20 40 60 80 100
... Meaning that knee valgus was greater for the 100% load condition. A modelling study by Vigotsky and Bryanton (2016) reported that the adductor magnus was the main hip extensor at lower barbell heights. However, the adductor magnus is also a hip adductor, which means that the participants in our study may have recruited the adductor magnus to a greater extent for the 100% load compared to the other condition due to larger hip adduction in all events (Figure 3). ...
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Shortly after beginning the upward phase of a free-weight barbell back squat there is often a deacceleration phase (sticking region) that may lead to repetition failure. The cause for this region is not well understood. Therefore, this study investigated the effects of 90%, 100%, and 102% of 1-RM barbell loads on kinematics, kinetics, and myoelectric activity in back squats. Twelve resistance-trained healthy males (body mass: 83.5 ± 7.8 kg, age: 27.3 ± 3.8 years, height: 180.3 ± 6.7 cm) participated in the study and lifted 134 ± 17 kg at 90% and 149 ± 19 kg at 100%, while they failed at 153 ± 19 kg with 102% load. The main findings were that barbell displacement and barbell velocity in the sticking region decreased with increasing loads. Moreover, the external hip extensor moment increased with heavier loads, whereas the knee extension and ankle plantarflexion moments were similar during the concentric phase. Also, reduced hip and knee extension together with lower myoelectric activity for all hip extensors and vastus lateralis were found for the 102% load compared to the others. Our finding suggests that the increased external hip extensor moment together with lower hip extensor myoelectric activity due to a reduced hip extension and thereby are responsible for lifting failure among resistance-trained males. ARTICLE HISTORY
... This is supported by Bryanton et al. (2012) who investigated both squat depth and barbell load on the relative hip, knee, and ankle muscular effort between 50 and 90% of 1-RM in back squats and found that the knee extensor relative muscle effort (the ratio of net joint moment to maximum voluntary torque, matched for joint angle) increased with deeper knee flexion angles, but not barbell load. The HBNS produced less gluteus maximus activity in the presticking region compared with other squat conditions, which is logical since increased depth lengthens the gluteus and reduces its capability to produce force (Vigotsky and Bryanton, 2016). However, no significant differences were observed in myoelectric activity for the vastus medialis. ...
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Barbell placement and stance width both affect lifting performance in the back squat around the sticking region. However, little is known about how these squat conditions separately could affect the lifting performance. Therefore, this study investigated the effects of stance width and barbell placement upon kinematics, kinetics, and myoelectric activity around the sticking region during a three-repetition maximum back squat. Nine men and nine women (body mass: 76.2 ±11.1, age: 24.9 ± 2.6) performed back squats with four different techniques, such as: high-bar narrow stance (HBNS), high-bar wide stance, low-bar narrow stance, and low-bar wide stance where they lifted 99.2 ± 23.6, 92.9 ± 23.6, 102.5 ± 24.7, and 97.1 ± 25.6 kg, respectively. The main findings were that squatting with a low-bar wide stance condition resulted in larger hip contributions to the total moment than the other squat conditions, whereas squatting with an HBNS resulted in greater knee contributions to the total moment together with higher vastus lateralis and less gluteus maximus myoelectric activity. Our findings suggest that training with an HBNS could be beneficial when targeting the knee extensors and plantar flexors, whereas a low-bar wide stance could be beneficial when targeting the hip extensors.
... Um allerdings hinsichtlich dieser Probleme nicht pauschal der Analyse von Gelenkmomenten jeglichen Mehrwert abzusprechen, sollte zunächst geklärt werden, wie stark die antagonistische Co-Kontraktionswirkung bei einer Übung ist. Für die Kniebeuge berechnetenVigotsky und Bryanton (2016), dass im Knie nur eine geringfügige und dazu konstante Co-Kontraktionswirkung durch die ischiokrurale Muskulatur besteht(Vigotsky & Bryanton, 2016). Arabatzi und Kellis (2012) berichten zudem, dass ein Gewichthebertraining die Co-Kontraktion der ischiokruralen Muskeln als spezifische Anpassung sogar reduziert. ...
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Previous investigations of strength have only focused on biomechanical or psychological determinants, while ignoring the potential interplay and relative contributions of these variables. The purpose of this study was to investigate the relative contributions of biomechanical, anthropometric, and psychological variables to the prediction of maximum parallel barbell back squat strength. Twenty-one college-aged participants (male = 14; female = 7; age = 23 ± 3 years) reported to the laboratory for two visits. The first visit consisted of anthropometric, psychometric, and parallel barbell back squat one-repetition maximum (1RM) testing. On the second visit, participants performed isometric dynamometry testing for the knee, hip, and spinal extensors in a sticking point position-specific manner. Multiple linear regression and correlations were used to investigate the combined and individual relationships between biomechanical, anthropometric, and psychological variables and squat 1RM. Multiple regression revealed only one statistically predictive determinant: fat free mass normalized to height (standardized estimate ± SE = 0.6 ± 0.3; t(16) = 2.28; p = 0.037). Correlation coefficients for individual variables and squat 1RM ranged from r = -0.79-0.83, with biomechanical, anthropometric, experiential, and sex predictors showing the strongest relationships, and psychological variables displaying the weakest relationships. These data suggest that back squat strength in a heterogeneous population is multifactorial and more related to physical rather than psychological variables.
  • Escamilla
Escamilla, et al., Med. Sci. Sports Exerc. 33(6), 984-98, 2001.
  • Bryanton
Bryanton, et al., J. Strength Cond. Res. 26(10), 2820-8, 2012.
  • Bryanton
Bryanton, et al., Sports Biomech. 14(1), 122-38, 2015.
  • Handsfield
Handsfield, et al., J. Biomech. 47(3), 631-8, 2014.
  • Hawkins
Hawkins, et al., J. Biomech. 23(5), 487-494, 1989.
  • Scand Nemeth
Nemeth, Scand. J. Rehabil. Med. Suppl. 10 1-35, 1984.
  • Delp
Delp, et al., IEEE Trans. Biomed. Eng. 37(8), 757-67, 1990.
  • Pedotti
Pedotti, et al., Math. Biosci. 38(1-2), 57-76, 1978. 10. Gorsuch, et al., J. Strength Cond. Res. 27(9), 2619-2625, 2013.
  • Byrne
Byrne, et al., J. Electromyogr. Kinesiol. 15(6), 564-75, 2005.
  • Fonseca
Fonseca, et al., J. Strength Cond. Res. 28(11), 3085-92, 2014.