Saudi Journal of Sports Medicine

ORIGINAL ARTICLE
Year
: 2022  |  Volume : 22  |  Issue : 2  |  Page : 74--81

Effects of concentric and eccentric exercises in the rehabilitation of flexible flat foot - A randomized trial


Hariharasudhan Ravichandran, Kshama Susheel Shetty, Samatha Ashok Shetty 
 Department of Physiotherapy, Alvas College of Physiotherapy, Dakshina Kannada, Karnataka, India

Correspondence Address:
Dr. Hariharasudhan Ravichandran
Department of Physiotherapy, Alvas College of Physiotherapy, Dakshina Kannada - 574 227, Karnataka
India

Abstract

Background: Flexible flat feet are one of the common presentations in the lower limb, which may be associated with postural stability, pathologies, and injuries. There are intrinsic and extrinsic causes for flat feet. Strengthening of muscles supporting the medial arch is the major goal in rehabilitating individuals with flat feet. Both concentric and eccentric strengthening programs are implemented in the rehabilitation of flat feet. Objectives: The objective of the study is to compare the effectiveness of concentric and eccentric exercise programs on improving navicular drop in adults with pronated feet. Materials and Methods: One hundred and four participants, between the age group of 18 and 25 years, were screened for pronated feet. Fifty-four participants fulfilling the inclusion and exclusion criteria were randomly assigned to either concentric (n = 27) or eccentric exercise group (n = 28). Both the groups performed their assigned exercise programs, either concentric or eccentric tibialis posterior strengthening exercises, respectively, for a duration of 6 weeks. Navicular drop test outcomes were assessed at baseline and postintervention. Results: The data were analyzed using IBM SPSS 20.0 version. Within-group analysis was performed using paired “t”-test, while between-group analysis performed using independent “t”-test. Postinterventional outcome was similar in both groups, and concentric group had significant outcomes (P = 0.006) in weight-bearing navicular drop test compared to eccentric group. There exists no statistical significance (P < 0.05) between the groups in improving medial longitudinal arch. Conclusion: Both concentric and eccentric exercises were equally effective in improving the medial longitudinal arch among participants with flexible flat foot. Future studies with long-term follow-up are recommended to validate the results of this study.



How to cite this article:
Ravichandran H, Shetty KS, Shetty SA. Effects of concentric and eccentric exercises in the rehabilitation of flexible flat foot - A randomized trial.Saudi J Sports Med 2022;22:74-81


How to cite this URL:
Ravichandran H, Shetty KS, Shetty SA. Effects of concentric and eccentric exercises in the rehabilitation of flexible flat foot - A randomized trial. Saudi J Sports Med [serial online] 2022 [cited 2022 Oct 3 ];22:74-81
Available from: https://www.sjosm.org/text.asp?2022/22/2/74/355193


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 Introduction



Flat foot is one of the common concerns of individuals who present with musculoskeletal complaint and commonly reported in the physiotherapist practice. Flat feet or pes planus is one of the most common deformities in the foot, characterized by the absence of medial longitudinal arch of the foot.[1] Medial arch helps absorb and equally distribute the forces when the body is bearing weight in the upright posture and serves as a flexible base of support for the entire body.[2] Dynamic and static supporting structures such as muscles, ligaments, and bones contribute to the structure and integrity of the medial longitudinal arch. Any deviations in the supporting structures weaken, flatten, and lead to collapse of medial longitudinal arch.[3]

Structurally, flat foot is characterized by abduction of the forefoot and valgus deformity of the hind foot. It is classified as flexible and rigid, based on the structural and functional abnormalities of the arch. In the former type, the arch is visible in nonweight-bearing positions, but it is absent during weight-bearing activities. It is also characterized by medial rotation and plantar–flexion of talus, eversion of the calcaneus, and collapsed medial arch. In the latter type, the arch is absent during weight-bearing and nonweight-bearing activities.[4] Flexible flat foot, otherwise called adult-acquired flat foot, is most often caused by posterior tibialis tendon insufficiency.[5]

Although flat foot is increasingly common nowadays, its prevalence was commonly reported in the literature and several investigations have been performed related to flat feet by several researchers worldwide. There exists a variation in the prevalence of flat foot. It changes with age, type of population being investigated, and presence of other associated musculoskeletal pathologies. A high prevalence rate of 21%–57% is reported among children between 2 and 6 years, which was found to decline by 13.4%–27.6% in primary school children.[6] In adult population, it is reported as 5%–14% approximately by different researchers.[7],[8],[9] Recently, in one of the studies, the authors investigated the prevalence of flexible flat feet among adults aged between 18 and 21 years using navicular drop test and reported that 12.8% of males and 14.4% of females were affected by flat feet.[10] It affects females more frequently than males.

Factors such as age, gender, foot length, familial history, practicing the usage of footwear early in infanthood, body mass index, comorbid illness, associated with pain, fatigue in women, and urban residence were reported to be associated with flat foot.[11] Flat feet are also seen secondary to biomechanical causes (ankle equinus, valgus deformities, accessory navicular bone) ligamentous laxity, neuromuscular disorders, hereditary conditions (osteogenesis imperfecta, Down syndrome, and Marfan syndrome), collagen disorders (Ehlers-Danlos syndrome), and so on.[12] It is often difficult to identify the exact reason of flat foot in every individual because of the existence of various factors associated with developing it. Literature suggests three different theories for the development of flat foot. According to one theory, failure of muscles supporting the arch leads to flat foot; according to the second theory, weakness of passive ligamentous support around the arch leads to flat foot; and according to the third theory, failure of both muscles and ligaments leads to flat foot.[13] Many studies demonstrate that the posterior tibialis tendon is the main dynamic stabilizer of the arch with lesser contributions from the peroneus longus, flexor digitorum longus, and flexor hallucis longus. Tightness or any changes in Achilles tendon is associated with dysfunction of tarsal alignment that leads to dorsolateral displacement of the navicular bone cause chronic stress on posterior tibialis tendon eventually, leading to microtrauma and degeneration in the later stages.[3]

The function of posterior tibialis tendon is essential to maintain the gait pattern without any abnormal deviations. During gait cycle, the posterior tibialis tendon function is critical during the push-off phase. Posterior tibialis contracts to invert the foot and maintains the transverse tarsal joints in a closed pack position. Weakness of posterior tibialis tendon leads to failure of stability in the transverse tarsal joints during the push-off phase. The unopposed peroneal muscles abduct the forefoot due to weakness of posterior tibialis tendon. Loss of transverse tarsal joint stability and forefoot abduction displaces the calcaneal tendon laterally, leading to valgus deviation in the foot.[14]

Posterior tibialis tendon dysfunction shall be classified broadly into four stages according to Johnson and Strom. The first two stages I and II were characterized by a still flexible foot structure that can be considered to be ideal to undergo conservative line of management. The other two stages III and IV demonstrate rigid or fixed longitudinal arch which is flattened and associated with loss of integrity in the continuity of the spring ligament complex along with tilt of talus within the mortise in valgus position. Here, active compensation is not able to take place.[15]

Several methods of management techniques have been reported in the management of adult-acquired flat foot. Long-term goal of any flat foot rehabilitation program aims at strengthening of tibialis posterior muscle. Strengthening program begins with isometric and progressed to isotonic exercises. Concentric and eccentric types of exercises were routinely implemented in strengthening programs. Specific characteristics of these two types of exercises in the management of flexible flat foot are not sufficiently reported in the literature. Evidence on tibialis posterior muscle strengthening helps provide insights for rehabilitation professionals to include tibialis posterior-related conditioning program in the management of flexible flat foot. Gastrosoleus is the most commonly prescribed strengthened muscle for flat feet and identifying the deficiency of tibialis posterior muscle, and its rehabilitation remains incomplete in the management of flexible flat feet. Physiotherapy program aims to stretch gastrocnemius and soleus muscle groups to relieve the stress placed on tibialis posterior simultaneously strengthening of tibialis posterior, peroneal, and tibialis anterior were performed. Orthoses and taping were suggested to diminish the demand of the posterior tibialis tendon during the stance phase of gait cycle. Although intrinsic muscle helps in maintaining arch, the tibialis posterior plays an essential role in maintaining the medial longitudinal arch during dynamic weight-bearing and balance activities. For these reasons, strengthening of tibialis posterior muscle is most preferred in individuals with flat foot than the intrinsic muscles. In earlier days, concentric exercises were performed to strengthen the tibialis posterior muscle. Recently, the trend has been shifted toward eccentric strengthening of tibialis posterior muscle. Very few studies analyzed the effects of concentric and eccentric types of exercise in strengthening tibialis posterior muscle. The purpose of this study is to analyze the effects of implementing concentric and eccentric exercises for tibialis posterior in the management of flexible flat feet.

 Materials and Methods



Protocol

This study followed the guidelines of the CONSORT statement [Figure 1].{Figure 1}

Participants

The study was conducted at the Outpatient Physiotherapy Department of Alvas Health Center, Moodbidri, Dakshina Kannada, Karnataka, India. Individuals clinically diagnosed with flat foot by a clinical orthopedician were included in this study. The sample size was estimated with significance of 5% and power of the study 80% using G power version 3.1.9.4 (Franz Faul, Universitat Kiel, Germany). Fifty-five participants included in this study were individuals identified with flexible flat foot, and the participants were randomly allotted to concentric exercise group (n = 27) and eccentric exercise group (n = 28). Lottery method was used for random allocation. The selection criteria of the participants were both the genders, between 18 and 25 years of age, with flexible flat foot. The exclusion criteria included (i) individuals with fixed or rigid flat feet, (ii) individuals with ankle pain or injury or stages III and IV tibialis posterior dysfunction, recent injuries, or any fracture in the lower limb, (iii) individuals whoever not willing to participate, (iv) individuals undergoing some orthotic aids for the management of flat foot, (v) individuals undergoing any other therapies for flat foot, (vi) individuals with deformities in proximal joints, and (vii) individuals with systemic illness.

Ethical approval

Ethical approval for the study was obtained from the Institutional Ethical Committee Review Board (202111-0027002) of Alvas College of Physiotherapy, Moodbidri, Dakshina Kannada, Karnataka, India. Following the ethical committee approval, the study was conducted from November 2021 to February 2022. The study was carried out as per the standards set by the Ethical Committee Review Board of Alvas College of Physiotherapy, Moodbidri, Dakshina Kannada, Karnataka, India.

Outcome measures

Navicular drop test was performed at baseline and posttest following 6 weeks of concentric and eccentric exercises. This test was performed in weight-bearing and nonweight-bearing postures.

Procedures

Participants were screened and those who presented with flat foot were identified. Individuals who fulfilled the inclusion criteria were interviewed for their consent to participate in this study. Written consent was obtained from every participating student. The study purpose and protocol were explained to all the individuals in the regional language that they are familiar with. Their age, height, and weight were recorded for demographic statistics. Baseline navicular drop test was performed. This is a double-blinded study, in which baseline and postintervention assessments were performed by examiners, who were not aware of the participants' group or their allotted treatment. Each group received two different physiotherapists for providing treatment for the participants, and they are blinded from the baseline and postintervention outcomes.

Concentric exercise group

Participants performed following exercises; dorsiflexion with manual resistance, inversion of the foot with manual resistance, towel curls, heel raises with ball, and abduction of the foot with TheraBand. All the exercises were repeated 15 times and 3 sets daily, 4 days per week, for 6 weeks.

Concentric dorsiflexion with manual resistance

The participant is instructed to be seated in long sitting position on a mat with back supported and advised to perform dorsiflexion of the foot, while the therapist is giving resistance on the opposite side [Figure 2].{Figure 2}

Inversion of the foot with manual resistance

The participant is instructed to position in the long sitting position on a mat with back supported and advised to invert the foot, while the therapist is giving resistance on the opposite side [Figure 3].{Figure 3}

Towel curls

The participant is instructed to sit on a chair with back supported with towel placed below the feet and advised to lift the arch toward the body and repeat the process [Figure 4].{Figure 4}

Heel raises with ball

The participant is instructed to stand straight with ball placed between the malleolus of the participant and advised to balance the ball and raise the heel [Figure 5].{Figure 5}

Foot abduction with TheraBand

The participant is instructed to sit on a chair with feet touching the floor. One end of the TheraBand is fixed around the feet, and the other end of the band is held by the therapist to maintain resistance, and the subject is advised to abduct the feet [Figure 6].{Figure 6}

Eccentric exercise group

Participants in the eccentric exercise group performed the above-mentioned exercise by lengthening the muscle so that muscles contract eccentrically instead of concentric. Plantar flexion with manual resistance, eversion with manual resistance, towel curls, abduction of foot with TheraBand, and heel raises with ball on a stepper were all performed eccentrically. All the exercises were repeated 15 times and 3 sets daily, 4 days per week, for 6 weeks.

Eccentric dorsi flexion with manual resistance

The participant is positioned in high sitting with back support and instructed to plantar flex the foot slowly for a count of 10, while the therapist is giving resistance in the dorsum to plantarflex it. Repeat this process 15 times with three sets.

Eccentric invertor muscle contraction with manual resistance

The participant is positioned on side-lying on the test side and instructed to eccentrically contract the invertors so that slow eversion takes place, while the therapist is giving resistance in the opposite direction. Repeat this process 15 times with three sets.

Eccentric heel drop with a ball

The participant is instructed to stand upright on a stepper with heels outside the edge of the stepper, and a ball is placed between both the medial malleolus. The participant is instructed to hold the ball between the malleolus and simultaneously raise the heels and return back to neutral position slowly for a count of 7–10. This is repeated 15 times with three sets.

Towel curls

The participant is seated on a chair with a towel below his feet and instructed to lift the arch toward the body with minimal resistance given by the therapist on the towel and to relax the arch gradually for a count of 10. This is repeated 15 times three sets.

Foot abduction with TheraBand

The participant is seated on a chair with back supported and the foot placed over his knee (cross leg sitting), a TheraBand is fixed around the feet, the other end of the band is held by the therapist to maintain the resistance, and the participant is instructed to abduct the adducted foot slowly returning it back to neutral position. This process is repeated 15 times with three sets.

Data analysis

The statistical analysis for this study was done using IBM SPSS software version 22.0 (IBM Co, NY, USA). Descriptive/baseline data were analyzed for baseline similarity [Table 1]. Kolmogorov–Smirnov test is used to confirm normality of data. To test the hypothesis, t-test statistical analysis was performed to compare the means of two samples. Totally, 55 students provided their consent to participate in this study.{Table 1}

 Results



Mean age (standard deviation) of the participants in the concentric group was 20.88 (1.47) and in the eccentric group was 21.11 (1.55), respectively. Gender distribution occurred by chance and the principal investigator had no role in gender distribution. Right-sided flat foot was the most dominant side that was identified among the participating individuals. In the eccentric exercise group, left-sided flat foot was less compared to the concentric exercise group. There was no significant difference in navicular drop test performed in weight-bearing and nonweight-bearing positions in both the groups. Hence, baseline similarity of participants in both groups was assured [Table 1].

Paired t-test was used to measure the difference between the pretest and posttest values within groups. Independent t-test analysis was used to measure the posttest values between the groups.

One participant from Group B (eccentric exercise) discontinued the study due to personal reasons (out of station for a period of time). There were 27 participants in the concentric group and 27 participants in the eccentric group at the time of completion of the study. Within-group pre- and post-test analysis for weight-bearing navicular drop test was performed using paired t-test, at 5% level of significance. In the concentric exercise group, the calculated t-value for weight-bearing navicular drop test was −2.989, showing high significant (P = 0.006) improvement, whereas t-value for eccentric exercise group in weight-bearing navicular drop test (P = 0.184) and t-value for concentric (P = 0.713) and eccentric exercise in nonweight-bearing navicular drop test was not significant, showing that there is no difference in postinterventional outcomes among these groups in their respective outcomes [Table 2].{Table 2}

Between-group significance was analyzed by independent t-test at 5% level of significance. Posttest t-value obtained for weight-bearing navicular drop test and nonweight-bearing navicular drop test was 0.018 (P = 0.986) and −0.395 (P = 0.694), respectively. There was no significant difference between concentric and eccentric exercise group on weight-bearing navicular drop test and nonweight-bearing navicular drop test outcomes [Table 3].{Table 3}

 Discussion



The purpose of this study was to investigate the effects of concentric and eccentric tibialis posterior muscle strengthening in the management of flat foot. The result of this comparative study demonstrated that concentric and eccentric exercises had no significant differences in improving medial longitudinal arch among subjects with flexible flat foot. All the 54 participants completed the study without any known or serious adverse events. Compliance and adherence to exercise protocol was monitored by physiotherapist dedicated to each group.

Strengthening exercises of the plantar intrinsic foot muscles are often prescribed to flat-footed individuals because of the capacity of the intrinsic muscles to support the medial longitudinal arch of foot. In a recent study by Gheitsai et al.,[16] 36 adolescents with flat feet concluded that intrinsic muscle exercises were more effective in improving flat feet than extrinsic muscle exercises.

It is widely accepted that tibialis posterior provides dynamic stability for the medial longitudinal arch while performing activities such as walking and running. In addition, it is proposed that tibialis posterior muscle works in unison with the peroneus brevis, tibialis anterior, and gastrocnemius muscles during weight-bearing activities. When the tibialis posterior muscle fails, the others may fail as well.[17] However, it is unclear whether the intrinsic foot muscles are sufficient enough to support the medial longitudinal arch of foot.[18] Contrastingly, a study by Lee and Choi[19] demonstrated that combination of extrinsic (tibialis posterior) muscle strengthening and intrinsic muscle strengthening is effective in improving flexible flat feet. Hence, the present study was conducted to determine the effect of concentric and eccentric extrinsic muscle strengthening in improving flexible flat foot.

Similar to this study, Mulchandani et al.[20] stated that gluteal muscle strengthening has a significant effect on improving flat feet. Those authors proposed that gluteal muscle stabilizes the hip and counteracts hip adduction torque, and weak gluteal muscles lead to internal rotation of the femur contributing to the pronation of foot. Similarly, tibialis posterior contraction results in inversion and plantar flexion of the foot and elevated the medial longitudinal arch, which in turn locks the mid-tarsal bones, making the hind-foot and mid-foot rigid. This function of tibialis posterior helps gastrocnemius to work efficiently during the gait cycle. Weakness of tibialis posterior results in progressive collapse of the arch, drifts the heel in valgus, and abducts the forefoot.[21]

In this study, concentric and eccentric exercises of extrinsic (tibialis posterior) muscle are compared to determine the effective type of contraction that improves flexible flat feet. Concentric and eccentric types of muscle contractions are compared because the gains in eccentric training are reported to be superior to concentric training. In this study, pretest and posttest analysis of concentric exercise group revealed significance, which shows that there is some improvement in medial longitudinal arch following concentric exercise. This could be because tibialis posterior directly inserts into the navicular bone and its concentric contraction could pull the navicular bone in an attempt to increase the arch.[22] The pre- and post-test difference among individuals performing eccentric exercise was minimal and not significant. Possible mechanisms for not achieving significant results with eccentric exercise may be due to muscle architecture factors such as fascicle length and pennation angle and other factors such as neural specificity, velocity of movement, and transferability of strength gain to functional movements. Although the concentric exercise had significant P value after the intervention, there exists no significance when the posttest mean is compared between both the groups. This demonstrates that there exists no difference between concentric and eccentric exercise in the management of flat foot.

In this study, intrinsic muscle strengthening or a control group is not included, and hence, concentric or eccentric extrinsic muscle strengthening alone could not able to improve navicular drop significantly, and hence, both concentric and eccentric exercises are considered to be equally effective in the management of flexible flat foot. Limitations of this study were limited sample size, short intervention duration, lack of long-term follow-up data, lack of control group and intrinsic muscle strengthening as an adjunct or background intervention, and outcome measures such as manual muscle testing being not included.

 Conclusion



Although there was a slight improvement in the medial longitudinal arch in the individuals following concentric exercise, the study results conclude that both concentric and eccentric exercises are equally effective in the management of flexible flat foot. Future studies comparing concentric and eccentric, extrinsic muscle strengthening with the inclusion of intrinsic muscle training could provide more insight regarding it.

Acknowledgment

We would like to thank Alvas Education Foundation and Alvas Health Center for the facilities and support provided.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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