Physical Therapy Korea

The range of motion (ROM) of ankle dorsiflexion (DF) refers to the degree to which the foot can be actively or passively flexed towards the shin [1]. A deficiency in DF ROM is associated with various complications, including chronic ankle instability, impaired ankle mechanics, and lower limb dysfunctions [2]. For instance, limited DF during gait may prevent the ankle from achieving the ‘closed pack position’ during mid-stance, increasing the risk of sprain [3]. Therefore, maintaining adequate DF ROM is essential for functional movement in daily activities and exercise [1].

DF play a key role in dynamic activities such as walking. The normal maximum DF ROM of the ankle is approximately 20°, while at least 10° of DF is required for normal foot function and gait [4]. During the stance phase of gait, maximum DF occurs just before heel-off, when the knee is nearly fully extended [5]. If DF is restricted, it can interfere with the full closure of the ankle joint, leading to an unstable stance and an increased risk of injury.

Various interventions and clinical techniques can improve DF ROM. These interventions include methods for releasing gastrocnemius muscle tension, such as stretching exercises, relaxation techniques, and heat therapy [6]. Abe et al. [7] investigated the energy-efficiency of different treadmill inclines and analyzed gait characteristics based on speed and slope. The push-off of uphill treadmill walking requires a greater DF ROM compared to level ground walking and places more strain on posterior structures such as the Achilles tendon and calf muscles [1]. Although previous studies have demonstrated that uphill treadmill walking exercise (UTWE) can increase ankle ROM, research is lacking on the relationship between DF ROM and ankle peak torque in response to exercise interventions.

Therefore, this study aimed to evaluate the immediate effects of UTWE on DF ROM and ankle peak torque in individuals with limited DF. More, we sought to assess the changes in maximum DF ROM during the stance phase of gait, as well as the DF ROM in both open-kinematic-chain (OKC) and closed-kinematic-chain (CKC) conditions, along passive ankle peak torque, following a 30-minute UTWE in individuals with restricted DF mobility.

1. Participants

This study included 20 adults, consisting of 10 males and 10 females, with passive ankle DF of 5°–12° in a non-weight-bearing position and a mean age of 28 years [5]. The exclusion criteria were individuals with neurological disorders, metal implants in the treatment area, inability to walk independently, arthritis or inflammation in the lower extremities, or knee flexion contractures. All participants were fully informed about the study purpose and procedures, and written consent was obtained before inclusion in the study. The study was approved by the Institutional Review Board (IRB) of Yonsei University Mirae Campus (IRB no. 1041849-202404-BM-086-02).

2. Procedure

In this single-group pretest-posttest study, all participants underwent pre-assessments before the intervention, followed by a 30-minute UTWE. Post-assessments were conducted after the intervention.

3. Intervention

The UTWE was performed using a GOLDONE 100 treadmill (GOLDONE). To create the incline, five 5.5 cm blocks were placed under the front support of the treadmill, and a smartphone inclinometer was used to set the incline at 15° (Figure 1) [8]. The participants walked at a speed of 1.25 m/s for 10 minutes per set, completing three sets per session with a 5-minute rest between sets [9]. Although the incline was initially set at 15°, adjustments were made during the intervention to accommodate individual discomfort. Participants were instructed to distribute their weight evenly on both legs and avoid leaning on the handrails. A safety clip was attached to automatically stop the treadmill if the participant moved too far back, and they were advised to lightly hold the handrails for balance.

Figure 1. UTWE was performed on 15°. UTWE, uphill treadmill walking exercise. Revised from the article of Lee et al. (J Back Musculoskelet Rehabil 2024;37:707-13) [8].

4. Maximum DF ROM Measurement

The maximum DF ROM was measured under three different conditions (Figure 2).

Figure 2. Three ankle DF ROM measurement conditions. Maximum ankle DF ROM was measured under three different conditions. (A) Stance phase during gait maximum DF angle was measured until the heel off the ground. (B) OKC condition. (C) CKC condition. DF, dorsiflexion; ROM, range of motion; OKC, open-kinematic-chain; CKC, closed-kinematic-chain.

1) Maximum DF ROM during the stance phase of gait

Markers were placed on the lateral side of the 5th metatarsal, the lateral malleolus, and the midpoint between the lateral malleolus and fibular head of the restricted foot [9]. Maximum DF ROM during the stance phase was measured just before heel-off using the Image J software (version 1.54; National Institutes of Health). ROM was calculated by subtracting the flexed angle from the neutral 90° position. For each participant, 10 consecutive steps were recorded, and the middle four steps were analyzed, excluding the first and last three steps, to calculate the mean ROM.

2) DF ROM in OKC condition

In the OKC condition, a single skilled physical therapist used a goniometer to assess the passive ankle ROM. Participants were positioned in a prone position with the restricted foot hanging off the table. The 0° position was defined as the angle at the neutral position of the talocrural joint [10].

3) DF ROM in CKC condition

In the CKC condition, participants stood on their restricted heel, with their big toe positioned 10 cm away from a wall. They were instructed to move their knee forward, aiming for the second toe to touch the wall, without lifting their heel from the ground. Participants were allowed to lightly touch the wall with two fingers for balance [11].

5. DF and PF Peak Torque

Passive DF and plantar flexion (PF) peak torque were evaluated using a Biodex System Isokinetic Dynamometer (Mirion Medical [Biodex]). Participants were seated in the Biodex device with the restricted leg secured according to the user guide. Passive DF and PF were measured between 25° of PF and 15° of DF at a speed of 60 °/s, repeated 10 times (Figure 3) [6].

Figure 3. The Biodex System Isokinetic Dynamometer (Mirion Medical [Biodex]) is an isokinetic device used to measure peak torque values. Revised from the article of Kim et al. (Phys Ther Korea 2020;27:133-9) [6].

6. Statistical Analysis

Data were analyzed using Windows IBM SPSS software version 25.0 (IBM Co.). Descriptive statistics were used to analyze the general characteristics of the participants, and all variables were presented as means and standard deviations. Paired t-tests were performed to compare the differences in DF ROM and ankle peak torque values before and after the intervention, with the significance level set at p < 0.05.

This study enrolled a total of 20 adults, comprising 10 males and 10 females, with a mean age of 28 years and a passive DF range of 5°–12°. Table 1 shows the demographic characteristics and other relevant details of the study participants.

Table 1 . General characteristics (N = 20).

Variable	Value
Age (y)	28.2 ± 3.8
Height (cm)	170.5 ± 7.5
Weight (kg)	72.8 ± 20.1
BMI (kg/m2)	25.0 ± 5.7

Values are presented as mean ± standard deviation. BMI, body mass index..

1. Changes in Maximum DF ROM During the Stance Phase Before and After UTWE

The mean maximum DF ROM in the stance phase during gait increased from 8.54° ± 3.97° pre-intervention to 11.03° ± 4.41° post-intervention (Figure 4). The increase in DF ROM following the UTWE was statistically significant (p < 0.01).

Figure 4. Comparison of maximum DF ROM in the stance phase during gait: pre- and post-intervention. An increase in maximum DF ROM was observed as the angle decreased before and after the intervention. DF, dorsiflexion; ROM, range of motion. **p < 0.01.

2. Changes in DF ROM in OKC and CKC Conditions Before and After UTWE

The mean DF ROM in the OKC and CKC conditions increased from 8.90° ± 0.62° and 21.55° ± 0.72° pre-intervention to 18.00° ± 1.13° and 28.20° ± 1.00° post-intervention, respectively (Figure 5). The increases in DF ROM after the intervention were statistically significant (p < 0.0001).

Figure 5. Comparison of DF ROM in OKC and CKC conditions: pre- and post-intervention. Maximum DF ROM increased after the intervention. DF, dorsiflexion; ROM, range of motion; OKC, open-kinematic-chain; CKC, closed-kinematic-chain. ****p < 0.0001.

3. Changes in Maximum Peak DF and PF Torque Before and After UTWE

The group mean of peak torque values for DF and PF increased from 16.20 ± 1.28 N/m and 25.26 ± 2.51 N/m pre-intervention to 21.52 ± 1.39 N/m and 44.22 ± 4.20 N/m post-intervention, respectively (Figure 6). These changes in torque following the UTWE were statistically significant (p < 0.0002).

Figure 6. Comparison of DF and PF peak torque: pre- and post-intervention. Maximum DF ROM increased after the intervention. DF, dorsiflexion; PF, plantar flexion; ROM, range of motion. ***p < 0.001, ****p < 0.0002.

Restricted ROM in ankle DF has been identified as a contributing factor to mechanical dysfunctions in gait and other physical activities, such as walking and running [2]. Various physical therapy interventions, including stretching exercises, myofascial release, and thermotherapy, have been used to improve plantar flexor muscle flexibility and restore ankle function [6,12]. This study aimed to examine the immediate effects of a specially designed dynamic walking intervention, performed on a 15° incline treadmill, on improving DF ROM and torque generation in the ankle dorsiflexor and plantar flexor muscles.

The results showed a significant increase in maximum DF ROM during the stance phase of gait, indicating improved ankle flexibility and mobility post-intervention. Additionally, overall DF ROM significantly increased, highlighting the immediate positive impact of the intervention on joint mobility. Furthermore, torque generation for DF and PF muscles showed notable improvement, reflecting enhanced muscle performance and strength. This study suggests that UTWE offers rapid rehabilitation benefits for patients with limited ankle mobility; with repeated interventions, it has the potential to lead to long-term improvements in ROM, muscle strength, and functional performance.

Moreover, compared to previous studies, this intervention offers a selectively applicable treatment approach that promotes gastrocnemius muscle elongation and reduces muscle tightness, leading to greater ROM improvements [13]. These significant increases in DF ROM observed in both OKC and CKC conditions align with findings by Kwon and Shin [12], further validating the effectiveness of UTWE in improving ankle mobility and function in both non-weight-bearing and weight-bearing conditions. Additionally, the improvements in DF ROM support the findings by Weir and Chockalingam [4], who demonstrated that increased ankle ROM improves gait patterns and overall ankle function. The observed increase in peak torque values for both DF and PF muscles is consistent with the literature, highlighting the critical role of ankle strength in stability and injury prevention [14]. These results support the potential of UTWE to facilitate more functional and stable ankle movement, reducing the risk of injuries like sprains during gait [15].

Furthermore, the observed increases in both DF ROM and peak torque values suggest potential improvements in the length-tension relationship of the ankle muscles, which is crucial for maximizing tension and optimizing ankle functionality [16]. This dynamic improvement in ankle flexibility and strength can lead to improved propulsion during activities such as running and jumping, enhancing performance while reducing the risk of injury [17]. Therefore, these findings have significant implications for rehabilitation and enhancing athletic performance and dynamic movement efficiency, as supported by previous research [14].

However, this study has some limitations. The relatively small sample size limits the statistical power and generalizability of the findings, indicating the need for larger-scale studies to confirm these results. Moreover, only the effects of a single intervention session were examined, leaving the long-term impact of UTWE on ankle DF ROM and muscle torque uncertain. Future studies should consider longer intervention periods with follow-up assessments to determine the sustainability of these benefits. Moreover, the absence of a control or comparison group makes it challenging to attribute definitively the observed improvements solely to the intervention. Despite these limitations, these findings suggest that the UTWE effectively addresses the limitations of restricted ankle DF ROM and contributes to improving functional performance in individuals with limited ankle mobility. Future research should incorporate control groups or compare different interventions to strengthen the validity of the findings.

This study demonstrated that a 15° UTWE significantly improves ankle ROM and peak torque, enhancing ankle flexibility, strength, and function. This intervention could be beneficial for individuals with chronic ankle instability or those recovering from ankle injuries, indicating its potential as an effective method for rehabilitation and performance enhancement.

None.

None to declare.

No potential conflicts of interest relevant to this article are reported.

Conceptualization: SP, HSJ. Data curation: SP, YW, BSK. Formal analysis: SP, YW, BSK, HSJ. Investigation: SP. Methodology: SP, YW, BSK. Project administration: SP, HSJ. Resources: SP. Software: SP. Supervision: SP, YW, BSK, HSJ. Validation: SP. Visualization: SP. Writing - original draft: SP, HSJ. Writing - review & editing: SP, HSJ.