Evaluating the Function of the Foot Core System in the Elderly
Summary
The functional core stability of the foot contributes to the human static posture and dynamic activities. This paper proposes a comprehensive evaluation for the function of the foot core system, which combines three subsystems. It may provide increased awareness and multifaceted protocol to explore the foot function among different populations.
Abstract
As a complex structure to link the body and the ground, the foot contributes to postural control in human static and dynamic activities. The foot core is rooted in the functional interdependence of the passive, active, and neural subsystems, which combine into the foot core system controlling foot motion and stability. The foot arch (passive subsystem), responsible for load, is considered the functional core of the foot, and its stability is necessary for normal foot functions. The functional abnormalities of the foot have been widely reported in the elderly, such as weakness of toe flexor muscles, abnormal foot postures, and decreased plantar sensory sensitivity. In this paper, a comprehensive approach is introduced for evaluating the foot function based on foot core subsystems. The strength and morphology of the foot intrinsic and extrinsic muscles were used to evaluate the foot muscle (active subsystem) function. The doming strength test was applied to determine the function of foot intrinsic muscles, while the toe flexion strength test focused more on the function of extrinsic muscles. The navicular drop test and foot posture index were applied to evaluate foot arch (passive subsystem) function. For the neural subsystem, the plantar light touch threshold test and two-point discrimination test were used to assess plantar tactile sensitivity at nine regions of the foot. This study provides new insights into the foot core function in the elderly and other populations.
Introduction
The human foot is a highly complex structure, consisting of bones, muscles, and tendons that attach to the foot. As a segment of the lower extremity, the foot constantly provides direct source contact with the supporting surface and hence contributes to weight-bearing tasks1. Based on the complex biomechanical interplay between muscles and passive structures, the foot contributes to shock absorption, adjusts for irregular surfaces, and generates momentum. Evidence shows that the foot contributes meaningfully to postural stability, walking, and running2,3,4.
According to a new paradigm proposed by McKeon5 in 2015, the foot core is rooted in the functional interdependence of the passive, active, and neural subsystems, which combine into the foot core system controlling foot motion and stability. In this paradigm, the foot bony anatomy forms the functional half dome, which includes the longitudinal arches and transverse metatarsal arches and flexibly adapts to load changes6. This half dome and passive structures, including the ligaments and joint capsules, constitute the passive subsystem. Additionally, the active subsystem consists of foot intrinsic muscles, extrinsic muscles, and tendons. The intrinsic muscles act as local stabilizers responsible for supporting the foot arches, load dependence, and modulation7,8, while the extrinsic muscles generate foot motion as global movers. For the neural subsystem, several kinds of sensory receptors (e.g., capsuloligamentous and cutaneous receptors) in the plantar fascia, ligaments, joint capsules, muscles, and tendons contribute to foot dome deformation, gait, and balance9,10.
Several researchers have speculated that the foot contributes to daily activities in two main ways. One is by mechanical support via the functional arch and the modulation among lower limb muscles. The other is the input of plantar sensory information about the position11. Based on the foot core system, deficits in this system, including foot posture, the strength of intrinsic and extrinsic foot muscles, and sensation sensibility, may predispose to the weakness of mobility and balance9,11,12,13.
However, with advancing age, alterations to the aspect, biomechanics, structure, and function of the foot commonly occur, including foot or toe deformities, weakness of foot or toe strength, plantar pressure distribution, and reduced plantar tactile sensitivity14,15,16,17. The presence of toe deformity and the severity of hallux valgus are associated with mobility and fall risk in the elderly11,18. Moreover, the strength of toe flexor muscles, which used to be overlooked, contributes to balance in elderly people19. Meanwhile, the elderly are also at higher risks to have foot conditions associated with pathologies such as diabetes, peripheral arterial disease, neuropathy, and osteoarthritis20,21.
The assessment, examination, and health care of the foot, especially in the elderly, have attracted increasing attention14,21. However, there is a limited study to explore the comprehensive evaluation for the function of the foot core system. Numerous studies aimed to explore foot pathological problems in the elderly, such as pain and nail, skin, bone/joint, and neurovascular disorders21,22,23. The role of the foot in mechanical support and sensory input during daily activities and as a functional core system needs to be recognized and evaluated, which was ignored in previous studies. Especially, the foot active components, including the intrinsic and extrinsic muscles, works as the local stabilizers and global movers and contribute to the foot stability and behavior in static posture and dynamic movement5.
The toe flexion strength is singularly reported to represent foot muscle strength, and it's also utilized to explore the relationship between foot function and other health situations, such as balance, and mobility24,25,26. Inherently, the foot muscle strength is limited to distinguishing the action of intrinsic and extrinsic muscles. Moreover, several tests, including the paper grip test and an intrinsic positive test, were criticized as non-quantitative tests that have poor reliability and validity7,27. Recently, a new evaluation of foot doming strength was reported to quantify the intrinsic foot muscle strength and it has been shown to have a good validity28. By measuring the doming (short-foot movement) strength, it contributes to directly quantifying the function of intrinsic muscle.
Therefore, a protocol is proposed here aiming to explore the characteristics of the foot in the elderly based on the foot core system, especially the function of the active subsystem. This protocol provides a comprehensive assessment to investigate foot core stability, including the passive, active, and neural subsystem, in the elderly. Moreover, alterations in foot core function have been reported in several health situations, such as plantar fasciitis, flat foot, and diabetes24,29,30. In the future studies, it might help to evaluate the foot function among different populations in a multidimensional measurement.
Protocol
Representative Results
Discussion
The presented protocol is used to measure the characteristics of the foot in the elderly, which provides a comprehensive assessment to investigate foot core stability, including the passive, active, and neural subsystems. This new paradigm illuminates the foot function that interacts to stabilize the foot and sustain sensorimotor function in daily activities33. In previous studies, the researchers paid more attention to exploring foot deformity; toe flexion strength; diminished plantar sensory; an…
Divulgations
The authors have nothing to disclose.
Acknowledgements
The authors acknowledge the funding of the Breeding Program of Shanghai Tenth People's Hospital (YNCR2C022).
Materials
| Diagnostic Ultrasound System | Mindray | It is used in clinical ultrasonic diagnostic examination. | |
| ergoFet dynamometer | ergoFet | It is an accurate, portable, push/pull force gauge, which is designed to be a stand-alone gauge for capturing individual force measurements under any job condition. |
|
| Height vernier caliper | It is an accurate measure tool for height. | ||
| LabVIEW | It is a customed program software for strength analysis. | ||
| Semmes-Weinstein monofilaments | Baseline | It consists of 20 pieces, and each SWM haves an index number ranging from 1.65 to 6.65, that is related with a calibrated breaking force. | |
| Two-Point Discriminator | Touch Test | It is a set of two aluminum discs, each containing a series of prongs spaced between 1 to 15 mm apart. |
References
- Guidozzi, F. Foot problems in older women. Climacteric: The Journal of the International Menopause Society. 20 (6), 518-521 (2017).
- Zelik, K. E., Honert, E. C. Ankle and foot power in gait analysis: Implications for science, technology and clinical assessment. Journal of Biomechanics. 75, 1-12 (2018).
- Farris, D. J., Kelly, L. A., Cresswell, A. G., Lichtwark, G. A. The functional importance of human foot muscles for bipedal locomotion. Proceedings of the National Academy of Sciences of the United States of America. 116 (5), 1645-1650 (2019).
- Bruijn, S. M., van Dieen, J. H. Control of human gait stability through foot placement. Journal of The Royal Society Interface. 15 (143), 20170816 (2018).
- McKeon, P. O., Hertel, J., Bramble, D., Davis, I. The foot core system: a new paradigm for understanding intrinsic foot muscle function. British Journal of Sports Medicine. 49 (5), 290 (2015).
- McKenzie, J. The foot as a half-dome. British Medical Journal. 1 (4921), 1068-1069 (1955).
- Soysa, A., Hiller, C., Refshauge, K., Burns, J. Importance and challenges of measuring intrinsic foot muscle strength. Journal of Foot and Ankle Research. 5 (1), 29 (2012).
- Kelly, L. A., Cresswell, A. G., Racinais, S., Whiteley, R., Lichtwark, G. Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch. Journal Of the Royal Society Interface. 11 (93), 20131188 (2014).
- Galica, A. M., et al. Subsensory vibrations to the feet reduce gait variability in elderly fallers. Gait & Posture. 30 (3), 383-387 (2009).
- Park, J. H. The effects of plantar perception training on balance and falls efficacy of the elderly with a history of falls: A single-blind, randomized controlled trial. Archives of Gerontology and Geriatrics. 77, 19-23 (2018).
- Menz, H. B., Morris, M. E., Lord, S. R. Foot and ankle characteristics associated with impaired balance and functional ability in older people. The journals of gerontology. Series A, Biological Sciences and Medical Sciences. 60 (12), 1546-1552 (2005).
- Cobb, S. C., Bazett-Jones, D. M., Joshi, M. N., Earl-Boehm, J. E., James, C. R. The relationship among foot posture, core and lower extremity muscle function, and postural stability. Journal of Athletic Training. 49 (2), 173-180 (2014).
- Koyama, K., Yamauchi, J. Altered postural sway following fatiguing foot muscle exercises. PloS One. 12 (12), 0189184 (2017).
- Rodriguez-Sanz, D., et al. Foot disorders in the elderly: A mini-review. Disease-a-Month: DM. 64 (3), 64-91 (2018).
- Osoba, M. Y., Rao, A. K., Agrawal, S. K., Lalwani, A. K. Balance and gait in the elderly: A contemporary review. Laryngoscope Investigative Otolaryngology. 4 (1), 143-153 (2019).
- Gimunova, M., Zvonar, M., Mikeska, O. The effect of aging and gender on plantar pressure distribution during the gait in elderly. Acta of Bioengineering and Biomechanics. 20 (4), 139-144 (2018).
- Cen, X., Jiang, X., Gu, Y. Do different muscle strength levels affect stability during unplanned gait termination. Acta of Bioengineering and Biomechanics. 21 (4), 27-35 (2019).
- Mickle, K. J., Munro, B. J., Lord, S. R., Menz, H. B., Steele, J. R. ISB Clinical Biomechanics Award 2009: toe weakness and deformity increase the risk of falls in older people. Clinical Biomechanics. 24 (10), 787-791 (2009).
- Spink, M. J., et al. Foot and ankle strength, range of motion, posture, and deformity are associated with balance and functional ability in older adults. Archives of Physical Medicine and Rehabilitation. 92 (1), 68-75 (2011).
- Singhal, A., Segal, A. R., Munshi, M. N. Diabetes in long-term care facilities. Current Diabetes Reports. 14 (3), 464 (2014).
- James, K., Orkaby, A. R., Schwartz, A. W. Foot examination for older adults. The American Journal of Medicine. 134 (1), 30-35 (2021).
- Awale, A., et al. Foot function, foot pain, and falls in older adults: The Framingham foot study. Gerontology. 63 (4), 318-324 (2017).
- Stolt, M., Suhonen, R., Voutilainen, P., Leino-Kilpi, H. Foot health in older people and the nurses’ role in foot health care–a review of literature. Scandinavian Journal of Caring Sciences. 24 (1), 194-201 (2010).
- Kusagawa, Y., et al. Toe flexor strength is associated with mobility in older adults with pronated and supinated feet but not with neutral feet. Journal of Foot and Ankle Research. 13 (1), 55 (2020).
- Yamauchi, J., Koyama, K. Toe flexor strength is not related to postural stability during static upright standing in healthy young individuals. Gait & Posture. 73, 323-327 (2019).
- Uritani, D., Fukumoto, T., Matsumoto, D., Shima, M. The relationship between toe grip strength and dynamic balance or functional mobility among community-dwelling Japanese older adults: A cross-sectional study. Journal of Aging and Physical Activity. 24 (3), 459-464 (2016).
- Menz, H. B., Zammit, G. V., Munteanu, S. E., Scott, G. Plantarflexion strength of the toes: age and gender differences and evaluation of a clinical screening test. Foot & Ankle International. 27 (12), 1103-1108 (2006).
- Ridge, S. T., Myrer, J. W., Olsen, M. T., Jurgensmeier, K., Johnson, A. W. Reliability of doming and toe flexion testing to quantify foot muscle strength. Journal of Foot and Ankle Research. 10, 55 (2017).
- Wang, X., Chen, L., Liu, W., Su, B., Zhang, Y. Early detection of atrophy of foot muscles in Chinese patients of type 2 diabetes mellitus by high-frequency ultrasonography. Journal of Diabetes Research. 2014, 927069 (2014).
- Jung, D. Y., Koh, E. K., Kwon, O. Y. Effect of foot orthoses and short-foot exercise on the cross-sectional area of the abductor hallucis muscle in subjects with pes planus: a randomized controlled trial. Journal of Back and Musculoskeletal Rehabilitation. 24 (4), 225-231 (2011).
- Snyder, B. A., Munter, A. D., Houston, M. N., Hoch, J. M., Hoch, M. C. Interrater and intrarater reliability of the semmes-weinstein monofilament 4-2-1 stepping algorithm. Muscle & Nerve. 53 (6), 918-924 (2016).
- Redmond, A. C., Crane, Y. Z., Menz, H. B. Normative values for the Foot Posture Index. Journal of Foot and Ankle Research. 1 (1), 6 (2008).
- McKeon, P. O., Fourchet, F. Freeing the foot: integrating the foot core system into rehabilitation for lower extremity injuries. Clinics in Sports Medicine. 34 (2), 347-361 (2015).
- Navarro-Peternella, F. M., Teston, E. F., Dos Santos Santiago Ribeiro, B. M., Marcon, S. S. Plantar cutaneous sensory stimulation improves foot sensibility and gait speed in older adults with diabetes: A clinical trial. Advances in Skin & Wound Care. 32 (12), 568-573 (2019).
- Felicetti, G., Thoumie, P., Do, M. C., Schieppati, M. Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies. Journal of the Peripheral Nervous System: JPNS. 26 (1), 17-34 (2021).
- Park, D. J., Lee, K. S., Park, S. Y. Effects of two foot-ankle interventions on foot structure, function, and balance ability in obese people with Pes Planus. Healthcare. 9 (6), 667 (2021).
- Garth, W. P., Miller, S. T. Evaluation of claw toe deformity, weakness of the foot intrinsics, and posteromedial shin pain. The American Journal of Sports Medicine. 17 (6), 821-827 (1989).
- Machado, A. S., Bombach, G. D., Duysens, J., Carpes, F. P. Differences in foot sensitivity and plantar pressure between young adults and elderly. Archives of Gerontology and Geriatrics. 63, 67-71 (2016).
- Scott, G., Menz, H. B., Newcombe, L. Age-related differences in foot structure and function. Gait & Posture. 26 (1), 68-75 (2007).
- Protopapas, K., Perry, S. D. The effect of a 12-week custom foot orthotic intervention on muscle size and muscle activity of the intrinsic foot muscle of young adults during gait termination. Clinical Biomechanics. 78, 105063 (2020).
- Mickle, K. J., Angin, S., Crofts, G., Nester, C. J. Effects of age on strength and morphology of toe flexor muscles. The Journal of Orthopaedic and Sports Physical Therapy. 46 (12), 1065-1070 (2016).
- Endo, M., Ashton-Miller, J. A., Alexander, N. B. Effects of age and gender on toe flexor muscle strength. Journal of Gerontology: MEDICAL SCIENCES. 57 (6), 392-397 (2002).
- Mickle, K. J., Nester, C. J., Crofts, G., Steele, J. R. Reliability of ultrasound to measure morphology of the toe flexor muscles. Journal of Foot and Ankle Research. 6 (1), 12 (2013).
- Headlee, D. L., Leonard, J. L., Hart, J. M., Ingersoll, C. D., Hertel, J. Fatigue of the plantar intrinsic foot muscles increases navicular drop. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology. 18 (3), 420-425 (2008).
- Han, J., Park, S., Jung, S., Choi, Y., Song, H. Comparisons of changes in the two-point discrimination test following muscle fatigue in healthy adults. Journal of Physical Therapy Science. 27 (3), 551-554 (2015).
- Greenman, R. L., et al. Foot small muscle atrophy is present before the detection of clinical neuropathy. Diabetes Care. 28 (6), 1425-1430 (2005).
- Viseux, F. J. F. The sensory role of the sole of the foot: Review and update on clinical perspectives. Neurophysiologie Clinique = Clinical Neurophysiology. 50 (1), 55-68 (2020).
- Sakamoto, K., Kudo, S. Morphological characteristics of intrinsic foot muscles among flat foot and normal foot using ultrasonography. Acta of Bioengineering and Biomechanics. 22 (4), 161-166 (2020).
- Cheung, R. T. H., Sze, L. K. Y., Mok, N. W., Ng, G. Y. F. Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis. Journal of Science and Medicine in Sport. 19 (9), 713-715 (2016).
