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The Biomechanics of Pregnancy

Original Editor - Areeba Raja

Top Contributors - Areeba Raja, Kim Jackson and Rana Muhammad Tahir Aslam  

Introduction

Pregnancy, as a natural process produces a number of physiological changes in a woman's body. Weight gain in pregnancy challenges the musculoskeletal system to adapt accordingly. These progressions make both the stance and stride different for pregnant women from non-pregnant. These changes make both the posture and gait pattern of pregnant women different from non-pregnant women.[1]

As the fetus grows, the body's centre of mass also changes with it. The kinematic adjustments are made in order to improve stability, allowing safer gait for the pregnant woman in opposition to the anteriorly added mass on the trunk. However these modifications might be just mechanical in nature, diminishing the motor impact of the increased mass as total mass normalised moments decrease.[2]

Biomechanics Considerations

Various biomechanical and hormonal changes occur during pregnancy that can alter musculoskeletal alignments by affecting the key areas of the body such as spinal curvature, balance, and gait patterns and can greatly impact the quality of life (QOL) by increasing back pain and the risk of falls.[3]

The overall postural effect of pregnancy by the final month is as follows:[2][4][5][6][7][8][9]

  • Anterior tilt of the pelvis.
  • Hyperextended knees.
  • Increased lumbar lordosis.
  • Posterior shift of gravity line.
  • Hyper kyphosis of the upper thoracic spine.
  • Protracted shoulders.
  • Anterior angulation of the cervical region.
  • Extension of the occiput on atlas.
  • Associated with these postural changes is a waddling gait pattern.


The video below demonstrates how posture changes as the fetus grows.

Changes in the Spine

  • Lack of positional adjustment in the lumbar curve occurs as the centre of mass translates anteriorly during pregnancy.[10]
  • The upper body becomes and unstable as the force of gravity becomes distant from the hip, generating a larger hip moment.[10]
  • In pregnancy women exhibit a sway-back posture. The upper trunk moves posterior to the lower body causing the centre of gravity to shift posteriorly, and causing an increase in the tone of head and neck muscles, causing the head to shift anteriorly in order to compensate the shift of centre of gravity and prevent falling.[10]

Changes in the Knee

  • Pregnant women tend to compensate anterior shift in centre-of-gravity by hyperextending their knees, so that they can maintain their balance and upright posture. Anterior cruciate ligament (ACL) adapts to the demands put on the knee because of hypertension and lengthens throughout the pregnancy as a result of impingement against the femoral notch .[11]
  • Laxity in the knee increases early in the pregnancy and decreases significantly in the postpartum period [12]
  • The changes in the joint laxity can persist following pregnancy making the women prone to developing OA and other musculoskeletal conditions [11]

Changes in the Ankle and Foot

  • An increase in the circumference of the foot and reduction in the plantar arch occurs as a result of biomechanical changes during pregnancy and puerperium. Whereas weight gain and ligamentous laxity can cause an increase in the foot's length and width.
  • During pregnancy, the exertion of forces shift from the posterior to the anterior feet with resulting increments at the forefoot and, predominantly, at the midfoot.[13]
  • Inflammation of plantar fascia can occur as a result of added stress due to flat feet.[14]
  • The centre of mass relocates as the bodyweight increases, redistributing the plantar load, which is reported to be correlated with foot complaints.[15]

Balance Strategies in Pregnancy

An increment of 15 to 25 percent in the woman's body weight occurs during pregnancy which implies relatively greater stress on the joints and associated structures (e.g. tendons and ligaments) whereas the growing fetus and increase breast volume causes the centre of gravity to shift to the front.[16] Considering all the biomechanical alterations during pregnancy, balance tends to decrease causing a negative impact on postural stability and high risk of fall, especially in the third trimester.[17][18]

To avoid falls and control medial-lateral balance pregnant women tend to rely on feedforward mechanism instead of feedback mechanism.[19] Increase in postural sway in anteroposterior direction causes degradation in the perceived balance. However, reduction in perceived and actual stability is compensated by increase stance width which helps preserve the lateral balance in pregnant women.[20]

Furthermore, Women's reliance on the visual cues increases during pregnancy.[21] Whereas, there is degradation in forward reach distance in pregnant women compared to non-pregnant and the ankle joint strategy takes over the hip joint strategy.[22]

Biomechanical Alterations in Gait

Locomotion is the most fundamental everyday action for the human body; however, in pregnancy, several biomechanical changes can be noticed in the gait.[23] Alteration in the gait pattern is the result of adaptations made as opposed to the weight gain and the shift of centre of gravity. The gait of pregnant women undergoes following modifications:[1][23][24]

Gait Speed

The gait of pregnant women is described by slower speed as compared to the pre-pregnancy and postpartum state.[1][25] The large relative phase between pelvic and thoracic rotations is avoided by the pregnant women that is typical for high strolling speeds, possibly because of the increase in the moments of inertia of their pelvis and thorax which makes the command of relative phase more critical.

Gait Cycle

There is a significant decrease in the length of the gait cycle in pregnant women and an increase in double support time compared to post-partum and nulliparous women, exaggeration of the transition phases occur in order to increase the security of gait.[26] [27]

Table below

Spatial and Temporal Parameters of Gait
Stride Length decreases as pregnancy progresses[3][28][29][30][26]
Stride Width remains unchanged[29]
Step Length Decreases[26][31]
Step Width Increases as the pregnancy progresses[3][26][28][30]
Single Support Time Decreases[3][26][31]
Double Support Time Increases between trimesters[3][29][26][31]
Base of Support Increases[3][9][26]
Ground Reaction Force Decrease in late pregnancy.[31][32][33]
Joint Kinematic Parameters
Sagittal Plane
Pelvis Increase in anterior tilt about 5 degrees[26][34]
Hip Increase flexion during stance phase[7][26][35]
Knee Increase flexion during terminal stance[26]
Ankle Decrease dorsiflexion and plantarflexion[7][26]
Frontal Plane
Pelvis Increase in pelvic separation width and reduction in the amplitude of the unilateral elevation of the pelvis.[26]
Hip Decrease in abduction.[15]
Joint Kinetic Parameters
Sagittal Plane
Hip Significant increase in the hip extensors moment[26]
Knee Significant decrease in the knee extensor moment[26]
Ankle Significant decrease in the ankle plantar flexor moment[26]
Frontal Plane  
Hip Increase in hip abductors moment[26]
Knee Increase in knee adductors moment[26]

[36]

Sit-to-Stand during Pregnancy

With the progression in pregnancy rising to stand from a chair becomes more difficult, which may lead the body to adapt according to the biomechanical modifications and musculoskeletal demands. [37] [38] Following temporal-spatial, kinematic and kinetic strategies can be used by the pregnant women during the transfer:[39]


Utilizing the biomechanical changes owing to increased uterus volume, the pregnant women will deliberately restrict the propulsive impulse in order to keep up with upright balance and upstanding position at the end of rising to stand. To guarantee safe movement, pregnant women ought not to start steps until arriving at a steady standing situation subsequent to rising.[37]

The video below shows the safe way of transference from sitting to standing during pregnancy

[40]

Stand-to-Sit during Pregnancy

The following changes occur in the kinematic performance of stand-to-sit during pregnancy:[41]
  • Hip and spine motion change in pregnancy while sitting from a standing position as hip range of motion and standing angle changed in favor of spine motion.
  • Postural changes identified with gestational lordosis influence the transference from a standing position to sitting.
  • Coordination changes away from the hip during the initial and terminal phases of sitting:
  1. Joint coordination shifts from hip dominant to spine- and shoulder-dominate coordination not long before the beginning of sitting movement.
  2. Hip-knee joint coordination not long before seat contact shifts from hip to a knee-predominant movement during pregnancy

Discomforts of Pregnancy

A wide variety of musculoskeletal problems can be reported during pregnancy as it induces a variety of biomechanical, hormonal, and vascular changes. The growing fetus alters the body’s centre of gravity applying mechanical stress on the body. Laxity in the joints develops secondary to hormonal changes. Compression of soft tissues in pregnancy can occur because of fluid retention. Consequently, making a pregnant woman prone to musculoskeletal injuries.[42]

Postural changes during pregnancy may cause the following complaints:[43][10][42]

Implications for the Physiotherapist

During pregnancy, the biomechanical alteration of the posture should be examined by a physiotherapist early in the ante-natal program. Monitoring postural changes initially and revaluating as the pregnancy progresses is important in order to take suitable preventative and therapeutic measures, and to encourage the maintenance of 'good posture'. A simple inclinometer or clinometer can be used to monitor the postural changes, and the data gathered by the comprehensive recording could help the physiotherapist to explore the influence of postural changes on the development of pain during pregnancy.[44]

See antenatal exercises and physical activity and pregnancy to learn more about therapeutic approach during pregnancy.

Clinical Bottom Line

The research proposes that there is a huge difference in each individual's postural adaptations during pregnancy, with, perhaps, each woman solving the problems in her own way but the influence of relative weight gain on postural and biomechanical adaptations during pregnancy demonstrates the importance of antenatal exercise programs .[45][46]

References

  1. ↑ 1.0 1.1 1.2 Forczek, W., & Staszkiewicz, R. (2012). Changes of kinematic gait parameters due to pregnancy. Acta of bioengineering and biomechanics, 14(4), 113–119.
  2. ↑ 2.0 2.1 Ogamba, M. I., Loverro, K. L., Laudicina, N. M., Gill, S. V., & Lewis, C. L. (2016). Changes in Gait with Anteriorly Added Mass: A Pregnancy Simulation Study. Journal of applied biomechanics, 32(4), 379–387 [cited 2025 Aug 22]
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Conder, R., Zamani, R., & Akrami, M. (2019). The Biomechanics of Pregnancy: A Systematic Review. Journal of functional morphology and kinesiology, 4(4), 72.
  4. ↑ Fligg D. B. (1986). Biomechanical and treatment considerations for the pregnant patient. The Journal of the Canadian Chiropractic Association, 30(3), 145–147.
  5. ↑ Yoo, H., Shin, D., & Song, C. (2015). Changes in the spinal curvature, degree of pain, balance ability, and gait ability according to pregnancy period in pregnant and nonpregnant women. Journal of physical therapy science, 27(1), 279–284.
  6. ↑ Gilleard, W. L., Crosbie, J., & Smith, R. (2002). Static trunk posture in sitting and standing during pregnancy and early postpartum. Archives of physical medicine and rehabilitation, 83(12), 1739–1744.
  7. ↑ 7.0 7.1 7.2 Ribeiro, A. P., João, S. M., & Sacco, I. C. (2013). Static and dynamic biomechanical adaptations of the lower limbs and gait pattern changes during pregnancy. Women's health (London, England), 9(1), 99–108.
  8. ↑ Ribeiro, A. P. (2015). Posture and gait biomechanical aspects during pregnancy and the importance of therapeutic exercise. ResearchGate. Bentham Science Publishers.
  9. ↑ 9.0 9.1 Forczek, W., Ivanenko, Y. P., Bielatowicz, J., & Wacławik, K. (2018). Gait assessment of the expectant mothers - Systematic review. Gait & posture, 62, 7–19.
  10. ↑ 10.0 10.1 10.2 10.3 Okanishi, N., Kito, N., Akiyama, M., & Yamamoto, M. (2012). Spinal curvature and characteristics of postural change in pregnant women. Acta obstetricia et gynecologica Scandinavica, 91(7), 856–861.
  11. ↑ 11.0 11.1 Chu, S. R., Boyer, E. H., Beynnon, B., & Segal, N. A. (2019). Pregnancy Results in Lasting Changes in Knee Joint Laxity. PM & R : the journal of injury, function, and rehabilitation, 11(2), 117–124.
  12. ↑ Dumas, G. A., & Reid, J. G. (1997). Laxity of knee cruciate ligaments during pregnancy. The Journal of orthopaedic and sports physical therapy, 26(1), 2–6.
  13. ↑ Varol, T., Göker, A., Cezayirli, E., Özgür, S., & Tuç Yücel, A. (2017). Relation between foot pain and plantar pressure in pregnancy. Turkish journal of medical sciences, 47(4), 1104–1108.
  14. ↑ Anees S. Ghait, Eman A. Elhosary, and Amr A. Abogazya. 2018. “Assessment of Foot Biomechanics through Measuring of the Plantar Pressure During the Last Trimester of Pregnancy”. Journal of Advances in Medicine and Medical Research 27 (7):1–6.
  15. ↑ 15.0 15.1 Mei, Q., Gu, Y., & Fernandez, J. (2018). Alterations of Pregnant Gait during Pregnancy and Post-Partum. Scientific reports, 8(1), 2217. ]
  16. ↑ Schröder, G., Kundt, G., Otte, M., Wendig, D., & Schober, H. C. (2016). Impact of pregnancy on back pain and body posture in women. Journal of physical therapy science, 28(4), 1199–1207.
  17. ↑ Inanir, A., Cakmak, B., Hisim, Y., & Demirturk, F. (2014). Evaluation of postural equilibrium and fall risk during pregnancy. Gait & posture, 39(4), 1122–1125.
  18. ↑ Cakmak, B., Ribeiro, A. P., & Inanir, A. (2016). Postural balance and the risk of falling during pregnancy. The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians, 29(10), 1623–1625. h
  19. ↑ Danna-Dos-Santos, A., Magalhães, A. T., Silva, B. A., Duarte, B. S., Barros, G. L., Silva, M. F. C., Silva, C. S., Mohapatra, S., Degani, A. M., & Cardoso, V. S. (2018). Upright balance control strategies during pregnancy. Gait & posture, 66, 7–12.
  20. ↑ Jang, J., Hsiao, K. T., & Hsiao-Wecksler, E. T. (2008). Balance (perceived and actual) and preferred stance width during pregnancy. Clinical biomechanics (Bristol, Avon), 23(4), 468–476.
  21. ↑ Butler, E. E., Colón, I., Druzin, M. L., & Rose, J. (2006). Postural equilibrium during pregnancy: decreased stability with an increased reliance on visual cues. American journal of obstetrics and gynecology, 195(4), 1104–1108.
  22. ↑ Takeda, K., Shimizu, K., & Imura, M. (2015). Changes in balance strategy in the third trimester. Journal of physical therapy science, 27(6), 1813–1817.
  23. ↑ 23.0 23.1 Zhang, Y., Lu, H., Gu, Y., & Hu, N. (2015). Characteristics of the centre of pressure progression for pregnant women during walking. International Journal of Biomedical Engineering and Technology, 17(4), 387-398.
  24. ↑ Bertuit, J., Leyh, C., Rooze, M., & Feipel, V. (2017). Pregnancy-related changes in center of pressure during gait. Acta of Bioengineering and Biomechanics, 19(4), 95-101.
  25. ↑ Sorani, D., Jani, R., & Anand, N. (2016). Gait analysis during pregnancy. International Journal of Health Sciences and Research, 6(7), 266-270.
  26. ↑ 26.00 26.01 26.02 26.03 26.04 26.05 26.06 26.07 26.08 26.09 26.10 26.11 26.12 26.13 26.14 26.15 26.16 Branco M, Santos-Rocha R, Vieira F. Biomechanics of Gait during Pregnancy. The Scientific World Journal [Internet]. 2014 [cited 2021 Nov 28];2014:1–5.
  27. ↑ Bertuit J, Feipel V, Rooze M. Temporal and spatial parameters of gait during pregnancy. 2015 [cited 2021 Nov 28];17(2).
  28. ↑ 28.0 28.1 Forczek W, Ivanenko Y, Curyło M, Frączek B, Masłoń A, Salamaga M, et al. Progressive changes in walking kinematics throughout pregnancy—A follow up study. Gait & Posture [Internet]. 2019 Feb [cited 2022 Jan 23];68:518–24.
  29. ↑ 29.0 29.1 29.2 Branco M, Santos-Rocha R, Aguiar L, Vieira F, Veloso A. Kinematic Analysis of Gait in the Second and Third Trimesters of Pregnancy. Journal of Pregnancy [Internet]. 2013 [cited 2021 Nov 27];2013:1–9.
  30. ↑ 30.0 30.1 Gilleard WL. Trunk motion and gait characteristics of pregnant women when walking: report of a longitudinal study with a control group. BMC Pregnancy and Childbirth [Internet]. 2013 Mar 20 [cited 2021 Nov 27];13(1).
  31. ↑ 31.0 31.1 31.2 31.3 Błaszczyk JW, Opala-Berdzik A, Plewa M. Adaptive changes in spatiotemporal gait characteristics in women during pregnancy. Gait & Posture [Internet]. 2016 Jan [cited 2021 Nov 27];43:160–4.
  32. ↑ Gimunova M, Kasović M, Zvonar M, Damir Knjaz. Analysis of ground reaction force in gait during different phases of pregnancy [Internet]. ResearchGate. unknown; 2015 [cited 2021 Nov 27].
  33. ↑ Branco M, Santos-Rocha R, Vieira F, Aguiar L, Veloso AP. Three-Dimensional Kinetic Adaptations of Gait throughout Pregnancy and Postpartum. Scientifica [Internet]. 2015 [cited 2021 Nov 28];2015:1–14.
  34. ↑ Foti T;Davids JR;Bagley A. A biomechanical analysis of gait during pregnancy. The Journal of bone and joint surgery American volume [Internet]. 2014 [cited 2021 Nov 28];82(5).
  35. ↑ Catena RD, Bailey JP, Campbell N, Stewart BC, Marion SJ. Correlations between joint kinematics and dynamic balance control during gait in pregnancy. Gait & Posture [Internet]. 2020 Jul [cited 2021 Nov 27];80:106–12.
  36. ↑ reference
  37. ↑ 37.0 37.1 Sunaga Y, Anan M, Shinkoda K. Biomechanics of rising from a chair and walking in pregnant women. Applied Ergonomics [Internet]. 2013 Sep [cited 2021 Nov 27];44(5):792–8.
  38. ↑ Lou S-Z, Chou Y-L, Chou P-H, Lin C-J, Chen U-C, Su F-C. Sit-to-stand at different periods of pregnancy. Clinical Biomechanics [Internet]. 2001 Mar [cited 2021 Nov 27];16(3):194–8.
  39. ↑ Gilleard W, Crosbie J, Smith R. A longitudinal study of the effect of pregnancy on rising to stand from a chair. Journal of Biomechanics [Internet]. 2008 Jan [cited 2021 Nov 27];41(4):779–87.
  40. ↑ reference
  41. ↑ Catena RD, Bailey JP, Campbell N, Music HE. Stand-to-sit kinematic changes during pregnancy correspond with reduced sagittal plane hip motion. Clinical Biomechanics [Internet]. 2019 Jul [cited 2021 Nov 27];67:107–14.
  42. ↑ 42.0 42.1 Kesikburun S, Güzelküçük Ü, Fidan U, Demir Y, Ergün A, Tan AK. Musculoskeletal pain and symptoms in pregnancy: a descriptive study. Therapeutic Advances in Musculoskeletal Disease [Internet]. 2018 Nov 19 [cited 2021 Nov 27];10(12):229–34.
  43. ↑ Britnell SJ, Cole JV, Isherwood L, Stan MM, Britnell N, Burgi S, et al. Postural Health in Women: The Role of Physiotherapy. Journal of Obstetrics and Gynaecology Canada [Internet]. 2005 May [cited 2022 Jan 24];27(5):493–500.
  44. ↑ BULLOCK JE, JULL GA, BULLOCK MI. The Relationship of Low Back Pain to Postural Changes During Pregnancy. Australian Journal of Physiotherapy [Internet]. 1987 [cited 2021 Nov 27];33(1):10–7. A
  45. ↑ Wu W, Meijer OG, Lamoth CJC, Uegaki K, van Dieën JH, Wuisman PIJM, et al. Gait coordination in pregnancy: transverse pelvic and thoracic rotations and their relative phase. Clinical Biomechanics [Internet]. 2004 Jun [cited 2021 Nov 27];19(5):480–8.
  46. ↑ Krkeljas Z. Changes in gait and posture as factors of dynamic stability during walking in pregnancy. Human Movement Science [Internet]. 2018 Apr [cited 2021 Nov 28];58:315–20.
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