Effects of Toe Tube Training on Intrinsic Foot Muscle Strength and Reactive Strength Index in Runners: A Randomized Controlled Trial

Abstract

Long-distance runners are known to be at a high risk of lower limb disorders due to a decline in the function of the intrinsic foot muscles (IFMs). The aim of this study was to examine the effects of toe tube training using elastic tubes. First, a crossover study was conducted with 13 healthy adults in three conditions: tube training, short foot exercise, and control. Changes in the IFMs pre- and post-exercise were confirmed using ultrasound echo. Next, 19 university long-distance runners were randomly divided into two groups (tube training or short foot exercise) and underwent a five-week training intervention. The toe grip strength, toe gap strength, and reactive strength index were measured pre- and post-intervention. In a crossover study, the tube training and short foot exercise showed a significant interaction effect on the abductor hallucis brevis (F = 5.63, p = 0.010, partial η² = 0.32) and flexor digitorum brevis (F = 15.29, p < 0.001, partial η² = 0.56), confirming an immediate effect of tube training and short foot exercise. In an intervention study with runners, no interaction was observed but a main effect of time was found, with both groups showing significant improvements in toe grip strength (F = 25.64, p < 0.001, partial η² = 0.60), toe gap strength (F = 11.26, p = 0.004, partial η² = 0.40), and RSI (F = 4.81, p = 0.042, partial η² = 0.22). Tube training may be an effective alternative for runners who find short foot exercise difficult and want to adjust the exercise load.

1. Introduction

In sports, lower limb disorders include a variety of disorders such as medial tibial stress syndrome, tibial overtired fatigue fractures, and chronic exercise compartment syndrome [1]. These are known to occur more frequently, particularly in long-distance runners [1]. Reduced intrinsic foot muscle (IFM) function is one of the contributing factors. A decrease in the medial longitudinal arch height (navicular drop) due to reduced IFM causes malalignment [2], which in turn leads to reduced dynamic balance and is associated with disability [3]. IFM exercises have been shown to reduce the incidence of disability [4], and improve vertical and horizontal jump performance [5]. The IFM strength is important not only for disability prevention but also for performance improvement. Concerning the IFMs, the abductor hallucis (AbH), flexor hallucis brevis (FHB), and flexor digitorum brevis (FDB) muscles play an important role in toe flexion [6] and their muscle size has been reported to correlate with toe strength [7]. Runners with smaller cross-sectional areas of the AbH have also been reported to have a history of injuries such as medial tibial stress syndrome, patellofemoral pain, and plantar fasciitis [8]. In runners, the toe strength is an important factor in injury prevention and competitive performance.

A well-known conventional IFM exercise is the short foot exercise (SF-ex) [6,7,9,10], which has been shown to be effective in supporting the medial longitudinal arch [2]. However, challenges include the difficulty of learning the movement itself, the inability to adjust the load, and the lack of ankle joint movement. SF-ex is an exercise in which the foot is moved in a ‘foot-shortening’ manner without flexing the toes, but the movement itself is difficult to learn as it is not something we are normally aware of. Since SF-ex is difficult to teach and learn, a step-by-step training program is recommended. First, the therapist moves the athlete’s foot to experience the short foot movement in ‘passive mode’, and then the athlete progresses to ‘active support mode’, where they contract the IFMs to achieve the short foot position. Finally, the athlete moves to ‘active mode’, where they perform the exercise independently. These steps are effective, but time-consuming [10]. Load regulation in SF-ex is restricted to sitting or standing. Usually, when the IFMs are mobilized, this is accompanied by movement and therefore ankle joint movement, but SF-ex does not involve ankle joint movement. Conventional exercises such as SF-ex are IFM-specific and there are no functional toe exercises that involve ankle joint and toe movement and are combined with extrinsic muscles. Evidence on effective toe exercises is considered necessary.

On the other hand, the usefulness of elastic resistance (tubing or bands) for non-IFM exercises using the lower limbs is widely recognized [11,12]. This method has been widely used in rehabilitation medicine and the health and fitness industry for muscle strengthening purposes and has become a staple of training due to its low cost, simplicity, portability, and versatility of use [13]. The load can be adjusted by selecting the type of tubing and adjusting the resistance. The elastic tubing can be simply hooked to the target area of the body to be trained, and exercises with joint movements in any direction can be performed. If the tube is placed between the toes, it is easy to learn how to train the IFMs with ankle joint movement. This is the type of toe tube training that we examined in this study. It has been reported that IFMs can be trained particularly effectively with toe flexion exercises in the plantar flexed position of the ankle joint [14]. The research suggests that in maximum plantar flexion of the ankle joint, the extrinsic muscles are relaxed, but the IFMs are not affected in length by the ankle joint position, so IFM activity is increased. During running, ankle joint plantar dorsiflexion moves from approximately 10 degrees of dorsiflexion to 20 degrees of plantar flexion [15]. Thus, the IFMs would ideally be trained in the movement of the plantar dorsiflexion.

In addition, metatarsophalangeal (MTP) joint dorsiflexion and plantar flexion have been suggested to affect sprint performance [16,17]. In an analysis of energy patterns in the foot during sprinting, the MTP joint energy absorption was observed to be high and energy generation low from the early to late stance phase [18]. The researchers concluded that the performance could be improved by reducing the energy loss at the MTP joint. Furthermore, compared to being barefoot, wearing hard spikes has been shown to promote the plantar flexion of the MTP joint at the time of push-off, increasing the moment arm length and improving propulsion [19]. IFM activity during late stance contributes to plantar flexion of the MTP joint, leading to efficient push-off [20]. However, conventional IFM training, SF-ex, does not include resistance loading for MTP joint plantar flexion and does not involve ankle joint dorsiflexion, so it does not fully reflect the IFM function in actual running situations. On the other hand, toe tube training has the potential to overcome these issues and strengthen the IFMs in a late stance phase in a way that simulates actual running. To our knowledge, no exercises have trained the IFMs using tubing. This study aimed to determine the effects of elastic tube training on the intrinsic foot muscle strength and reactive strength index in runners.

2. Materials and Methods

2.1. Participants

Before the main study, a pilot study of tube training was conducted as a crossover study to verify its effectiveness for IFMs. Participants were 13 healthy adult males ([mean ± standard deviation]: age, 20.4 ± 0.5 years; height, 171.9 ± 7.1 cm; weight, 70.4 ± 14.1 kg; body mass index (BMI), 23.7 ± 3.9 kg/m²). The participants were defined as having no acute trauma (sprain, fracture, etc.) to the lower limbs within the past three months.

Participants for this main study were recruited from male university student runners from the track and field club of the Daiichi Institute of Technology in Kagoshima Prefecture, Japan ([mean ± standard deviation]: age, 19.7 ± 1.3 years; height, 169.6 ± 4.0 cm; weight, 54.0 ± 2.8 kg; BMI, 18.8 ± 0.8 kg/m²; athletic history, 9.1 ± 2.6 years; 5000 m personal best, 15 min 17 ± 24 s), in a randomized controlled trial. Twenty-three competitive runners with at least 5 years of competitive history, practicing six times a week and running an average of approximately 120 km per week, were evaluated; those with a history of back pain, spinal or neurological disease within 6 months or other conditions that might interfere with the performance of the training program were excluded from the sample. The sample size was calculated using G*Power (G*Power version 3.1., Heinrich-Heine-University Düsseldorf, Germany) with a partial eta-squared of 0.35 and an effect size of 0.73 by a previous study comparing toe flexor changes after a toe flexor training intervention in runners with a control group [21]. A power analysis indicated that a total of at least 8 subjects would be required to achieve a power value of 0.80 with p < 0.05. However, the present study planned to recruit 23 runners, similar to this previous study, to account for dropouts.

2.2. Ethics

The study was approved by the Ethics Committee of Daiichi Institute of Technology (21-003) and all participants were informed orally and in writing of the study objectives in accordance with the Declaration of Helsinki. Written consent was also obtained before the start of the study.

2.3. Procedures

A crossover study was conducted in three randomized intervention orders in three conditions: tube training, SF-ex, and control. Trial order was determined randomly using a random number table created in Microsoft Excel. The washout period was 1 week. Ultrasound echo was used to assess the immediate effect.

In the main study, the baseline assessments included a questionnaire on age, medical history, athletic history, and personal best for 5000 m. Body mass (kg) and height (cm) were determined using a weighing scale (Tanita MC-780A; TANITA, Tokyo, Japan) and a stadiometer (SECA 222; SECA, Hamburg, Germany) to calculate the BMI. Toe grip strength, toe gap strength, and reactive strength index (RSI) were then measured. Random sampling with SPSS version 28.0 (IBM, Armonk, NY, USA) was performed on 19 subjects who met the inclusion criteria for the two groups. They were randomly assigned to either the tube training group (10 participants) or the SF-ex group (9 participants) to ensure that there were no differences in the basic items in each intervention group. This is a centralized randomization system that uses software to automatically assign participants based on their basic information, thereby improving the confidentiality of the allocation. Each group performed the exercises four times a week for five weeks. Figure 1 shows the flowchart of the study.

2.4. Intervention Methods

Tube training consisted of tying a 1 m tube (color/strength: green/heavy, material: natural rubber, Thera-Band tubing; Hygenic Corporation, Akron, OH, USA) at each end in the long sitting position and tying two knots at the mid-ankle joint (Figure 2). The two knots were placed between the great toe and the second toe at the mid-ankle joint. The ankle joint was plantarly dorsiflexed against the elasticity of the tubing with the hand holding the opposite side of the tubing knot. The MTP and interphalangeal (IP) joints were held in a plantar-dorsiflexed position for 5 s with strength applied to the IFM to prevent extension of each joint. All other toes were also flexed while flexing. SF-ex involved shortening the foot in the anterior–posterior direction while trying to move the first metatarsal head (ball of the great toe portion) towards the heel without curling the toes [22]. It was considered to have been performed correctly if the participant raised the navicular tubercle and held the IFM with strength for 5 s without bending the toes or lifting the foot off the floor.

SF-ex started in the sitting position and increased in difficulty to standing on both feet [23]. For both conditions, the number of times per set was increased until each individual felt like a 7 (very hard) on the Borg CR-10 scale [24,25]. Thus, the exercises were performed with individual progressive loads. For example, if the number of repetitions per set was 15 at the beginning of the intervention and was a Borg CR-10 scale 7, the number of repetitions increased to 16, 17, etc. as the person gained practice. Three sets were performed alternating between the left and right leg with a 45 s rest. Each participant received direct instruction from a strength and conditioning specialist with a 16-year career in the field of exercises, which helped to deepen their understanding of the subject. One researcher (YN) assessed whether each participant performed the exercises correctly once a week and assessed the progressive load. The researcher also checked the participant’s exercise record sheet.

2.5. Data Collection and Analysis Methods

In the pilot study, ultrasound echo (SonImage MX1; KONICA MINOLTA, Tokyo, Japan) was used to measure changes in muscle cross-sectional area due to acute muscle swelling [26,27] in AbH, FHB, and FDB before and after each intervention condition. Immediate effects were validated with ImageJ software (ImageJ 1.53t; National Institutes of Health, Baltimore, MD, USA) [28]. The region of interest was calculated by enclosing it along the fascial boundary. The mean of each muscle cross-sectional area was calculated from three images of each muscle of each participant.

Toe grip strength was measured using a toe grip dynamometer (T.K.K.3362; Takei Scientific Instruments, Niigata, Japan). The reliability of this device has been reported [29]. Participants were seated on a 40 cm high chair, with the pelvis in the mid-pelvic position and the hip and knee joints in 90° flexion, according to the methods of previous studies [29]. The ankle joint was placed in a neutral position and strapped to minimize movement. After the heel stopper was adjusted to fit each participant’s heel, the first proximal phalanx was aligned with the grip bar. Measurements were taken twice each, alternating left and right, and the average of the maximum values was adopted. Participants received verbal encouragement while performing the test.

The toe gap strength was measured using a toe gap dynamometer (Checker-kun; Nissinsangyo, Saitama, Japan) to measure the pinching strength between the great toe and the second toe [30]. This device has a structure similar to that of a grip dynamometer. The toe gap strength was measured twice each, alternately on the left and right side, in the same posture as the toe gap strength, taking care not to lift the heel, and the average value of the maximum values was adopted. Participants received verbal encouragement during the test.

RSI measures how quickly an athlete can exert strength when moving from a single downward sinking movement (centrifugal movement) to an immediate jumping movement (centripetal movement). This can be measured by the movement of jumping down from a high place and immediately jumping back up, as in a drop jump, and is expressed as the ratio of the height of the jump to the time the athlete was in contact with the ground [31]. In other words, the higher the RSI, the more efficiently you can utilize the rebound from the ground, which is one of the most important factors for the running economy. Previous research has shown a correlation coefficient of 0.58 between the strength of the toe flexors and the rebound jump index [32]. In this study, RSI was calculated using the My Jump2 application (My Jump2 v.6.1.7; Carlos Balsalobre, Madrid, Spain) with the drop jump test filmed on an iPhone XR (Apple, Cupertino, CA, USA) at 1080p/240 fps [33]. This uses the high-frame-rate and high-screen-resolution video recording on the iPhone to derive the jump behavior [33]. The time of flight and all subsequent variables were calculated from the participant’s leg length and weight. RSI variables were provided from the output jump height (cm) and time of flight (ms). Total flight time was measured by manually selecting the first video frame in which the participant took off after the drop and the second frame in which they landed after the jump. My Jump 2 App calculates jump height from flight time using the following equation from Bosco et al.: h = t² × 1.22625 or h = (g × t²)/8. Here, h is the total displacement of the center of gravity in meters (height jumped), t is the total flight time in seconds, and g is the acceleration due to gravity (9.81 m/s²) [34]. Previous studies have confirmed a very high positive correlation coefficient of 0.93 or more between the ground contact time of a 40 cm drop jump using My Jump and a force platform, and the derived RSI [35]. The intraclass reliability of the RSI and contact time has also been confirmed to be 0.92 or more [35]. The participants were instructed to stand on the 40 cm platform with their feet shoulder-width apart, place their hands on their hips, jump straight up with the force of their landing, and jump as high as possible with a short ground contact time. Three measurements were taken to calculate the RSI, and the average value was used.

2.6. Statistical Analysis

Data for each item were expressed as mean ± standard deviation. The normality of data distribution was determined using the Shapiro–Wilk test. The pilot study data were checked for normality, and the effects pre- and post-intervention in the three conditions were compared using repeated measures of two-way analysis of variance. In the runner group, after confirming the normality of the data, the baseline information for each intervention group was compared using Student’s t-test [36]. Repeated measures of two-way analysis of variance were used to compare the effects of tube training and SF-ex on each item. Paired t-tests were used to compare the pre- and post-intervention data for each condition. Partial eta-squared (η²) was used to determine effect size. Effect sizes were defined as trivial (partial η² < 0.01), small (partial η² = 0.01–0.06), medium (partial η² = 0.06–0.14), and large (partial η² > 0.14) [37]. The effect size, Cohen’s d (d), calculated to compare before and after each intervention, met the following criteria: trivial (d < 0.20), small (d = 0.20–0.50), medium (d = 0.50–0.80), and large (d > 0.80) [38]. Statistical analyses were performed using SPSS version 28.0, and the significance level was set at 5%.

3. Results

The pilot study results showed that tube training and SF-ex exhibited a significant interaction for the AbH (F = 5.63, p = 0.010, partial η² = 0.32) and FDB (F =15.29, p < 0.001, partial η² = 0.56), but no significant interaction for the FHB (F = 2.73, p = 0.086, partial η² = 0.19). In the pre- and post-intervention comparison, for the three muscles (AbH, FHB, and FDB), the results for tube training were p = 0.001, d = 1.14, 95% confidence interval (CI) [0.42, 1.83]; p = 0.012, d = 0.82, 95% CI [0.17, 1.44]; and p < 0.001, d = 1.82, 95% CI [0.91, 2.70]. In the SF-ex, the results were p = 0.010, d = 0.85, 95% CI [0.19, 1.47]; p = 0.103, d = 0.49, 95% CI [−0.10, 1.06]; and p < 0.001, d = 1.52, 95% CI [0.69, 2.31]. In the control group, p = 0.574, d = 0.16, 95% CI [−0.70, 0.39]; p = 0.881, d = 0.04, 95% CI [−0.59, 0.50]; and p = 0.267, d = 0.32, 95% CI [−0.24, 0.88]. Therefore, the immediate effects of tube training and SF-ex were confirmed in the AbH and FDB.

In accordance with the exclusion criteria, 4 out of 23 participants were excluded from the analysis, and 19 participants were divided into each intervention. The basic information for each intervention group is shown in

Table 1. Participant characteristics at baseline.

	Tube Training Group (n = 10)	SF-ex Group (n = 9)	p
Age, years	19.4 ± 1.2	20.0 ± 1.5	0.342
Body height, cm	170.4 ± 4.1	168.7 ± 0.4	0.394
Body weight, kg	54.5 ± 3.2	53.6 ± 2.6	0.439
BMI, kg/m2	18.8 ± 0.5	18.8 ± 1.0	0.948
Toe grip strength, kgf	19.4 ± 4.3	20.1 ± 4.9	0.715
Toe gap strength, kgf	3.2 ± 0.9	3.7 ± 1.1	0.306
RSI	2.3 ± 0.3	2.4 ± 0.4	0.625

Data presented as mean ± SD. BMI = body mass index; RSI = reactive strength index.

. No significant differences were found in the basic information at baseline between any of the groups.

In the intervention study targeting runners, no interaction was observed in any of the items, but the main effect of time was confirmed, and both groups showed significant improvements in toe grip strength (F = 25.64, p < 0.001, partial η² = 0.60), toe gap strength (F = 11.26, p = 0.004, partial η² = 0.40), and RSI (F = 4.81, p = 0.042, partial η² = 0.22) (

Table 2. Changes in toe function pre- and post-intervention between groups.

		Between-Group Differences
		Main Effect by Time			Interaction
		F-Value	p	Partial η2	F-Value	p	Partial η2
Toe grip strength	Tube training	25.64	<0.001 **	0.60	0.270	0.610	0.02
	SF-ex
Toe grip strength	Tube training	11.26	0.004 **	0.40	0.656	0.429	0.04
	SF-ex
RSI	Tube training	4.81	0.042 *	0.22	0.670	0.424	0.04
	SF-ex

Data presented as mean ± SD. RSI = reactive strength index. * p < 0.05; ** p < 0.01.

).

Table 3. Changes in toe function pre- and post-intervention within the group.

		Within-Group Differences
		Pre-Intervention	Post-Intervention	Difference [95% CI]	p	Cohen’s d [95% CI]
Toe grip strength	Tube training	19.4 ± 4.3	23.3 ± 3.6	3.98 [1.91, 6.05]	0.002 **	1.37 [0.48, 2.24]
	SF-ex	20.1 ± 4.9	23.4 ± 4.4	3.24 [0.69, 5.80]	0.019 *	0.98 [0.15, 1.76]
Toe gap strength	Tube training	3.2 ± 0.9	3.8 ± 0.9	0.60 [0.29, 0.91]	0.002 **	1.37 [0.48, 2.24]
	SF-ex	3.7 ± 1.1	4.1 ± 1.2	0.37 [−0.24, 0.97]	0.200	0.46 [−0.24, 1.14]
RSI	Tube training	2.33 ± 0.31	2.55 ± 0.39	0.22 [0.01, 0.44]	0.046 *	0.73 [0.01, 1.42]
	SF-ex	2.41 ± 0.44	2.51 ± 0.62	0.10 [−0.16, 0.36]	0.396	0.30 [−0.38, 0.96]

Data presented as mean ± SD. RSI = reactive strength index; 95% CI = 95% confidence interval. * p < 0.05; ** p < 0.01.

shows the results of the changes in the toe function pre- and post-intervention within the group. In the tube training, significant increases were observed in all the items, including the toe grip strength (p = 0.002, d = 1.37), toe gap strength (p = 0.002, d = 1.37), and RSI (p = 0.046, d = 0.73). In the SF-ex group, significant increases were observed in the toe grip strength (p = 0.019, d = 0.98), but no significant differences were observed in the toe gap strength (p = 0.200, d = 0.46) and RSI (p = 0.396, d = 0.30).

4. Discussion

4.1. Interpretation of Results

To verify the effectiveness of tube training, this study first confirmed that tube training and SF-ex had a significant immediate effect on the AbH and FDB through a crossover study using ultrasound echo. Next, a randomized controlled trial targeting long-distance runners showed that both tube training and SF-ex equally improved the toe grip strength, toe gap strength, and RSI. In a previous study of 23 competitive runners, a 5-week toe flexor muscle training intervention including SF-ex resulted in a 16% increase compared to baseline [21]. In this study, tube training led to an increase of 20.6% in the toe grip strength, 18.7% in the toe gap strength, and 9.5% in the RSI. SF-ex led to an increase of 16.1% in the toe grip strength, 9.9% in the toe gap strength, and 4.2% in the RSI. Therefore, this training was able to demonstrate results that were equivalent to or better than those of previous research.

Although the SF-ex has shown a certain level of effectiveness, the issues that need to be resolved include the fact that it is difficult to learn, the load cannot be adjusted, and it does not involve movement of the ankle joint. In contrast, the tube training method allows one to feel the resistance of the tube and change the intensity, so it has the potential to be easily implemented according to the individual’s toe function. In addition, tube training involves the movement of the ankle joint. In the plantar flexion position of the ankle joint, the interphalangeal (IP) joint is extended due to the tenodesis action of the foot. This is because the anatomical differences between the extrinsic and intrinsic muscles of the foot cause the flexion and extension of the IP joint to change as the ankle joint moves between plantar and dorsal flexion. The extrinsic muscles of the foot attach to the distal phalanges, but the AbH and FHB muscles stop at the base of the first metatarsal bone via the sesamoid bone, and the FDB muscle stops on the lateral side of the base of the second to fifth metatarsal bones [39]. Therefore, while the extrinsic muscles have a flexion action on the distal interphalangeal (DIP) joint, the IFM does not have a flexion action on the DIP joint. Tube training applies force in the direction of MTP joint extension. When the tube is at its maximum extension and resistance is at its strongest, MTP joint flexion force is exerted. Tube training may have effectively trained the IFM by maintaining MTP joint flexion against the resistance of the tube while the IP joint was extended in the plantar flexion position of the ankle joint. In SF-ex, no force is applied in the direction of MTP joint extension, so these types of loads are not applied, and they would be difficult to understand in voluntary isometric contraction. On the other hand, it has been reported that the extrinsic muscles, the flexor hallucis longus and the flexor digitorum longus, contribute to strengthening toe-off [40]. In addition, the fibular muscles of the extrinsic muscles have been shown to contribute to ankle stability and to be activated during the late stance phase of running [41]. These extrinsic muscles are correlated with toe strength and have been shown to contribute to the generation of greater metatarsophalangeal joint flexion moments during exercise [7]. These studies suggest that both extrinsic and intrinsic muscles contribute to the generation of the metatarsophalangeal joint flexion moment, and that the coordinated activity of both is important. The advantage of tube training is the ability to train with a predominance of extrinsic muscles in the dorsiflexion position of the ankle joint, and with a predominance of the IFM in the plantar flexion position.

After 10 weeks of jump rope training, the RSI increased by 13%, which was associated with improved performance in the 3 km time trial [42]. In this study, the baseline overall RSI was slightly high at 2.37 because the participants were competitive runners in the 40 cm drop jump. And, in the 5-week intervention, the RSI increased by 9.5% in the tube training and 4.2% in the SF-ex. The jump height is the most common and practical indicator for evaluating an athlete’s explosive power [31]. A positive correlation exists between the strength of the toe flexors, including the IFM, and vertical jump performance [32]. In the vertical jump, the force generated by the hip extensors, knee extensors, plantar flexors, and toe flexors pushes against the ground, accelerating the body upwards. The flexor digitorum brevis helps to transmit the force of the lower limbs to the forefoot, and propels the body upwards in the trajectory of the jump [43,44]. This also has the effect of lifting the heel off the ground during a vertical jump, increasing the plantar flexion moment at the ankle joint [45]. Extrinsic toe flexor activity tends to increase in conjunction with an increase in triceps surae muscle activity, suggesting that the energy generated at the ankle joint is transmitted to the metatarsophalangeal joint [46]. From these results, it can be concluded that the toe flexors are important for controlling the generation of force during the push-off phase of the vertical jump, and tube training can strengthen the toe flexors in the plantar flexion position of the ankle joint. The improvement in the toe grip strength, toe grip strength, and RSI indicates that tube training is an effective training method that promotes coordinated activity of both extrinsic and intrinsic muscles.

Medial tibial stress syndrome is a common disorder among runners. In particular, approximately 15% of high school cross-country athletes develop the disorder during the three-month competition season, and approximately 44% develop it over a three-year follow-up period [47,48]. Recovery from this injury takes between six and eleven weeks to return to the original competitive level [49]. These research results suggest the importance of introducing effective programs for prevention and early recovery for runners. In this study, tube training was able to show improvements in toe function equivalent to SF-ex through a 5-week intervention. Tube training does not rely on gravity as resistance [50]. Therefore, the load can be adjusted, enabling the exercise to be performed even during the period of unweighting due to lower limb injury. Tube-training may also be an effective training method for runners who are unable to run due to injury and are recovering the injured area.

4.2. Practical Implications

First, load adjustment is easy: The athlete can easily adjust the load by changing the elastic tube’s color, length, and grip. Athletes can train according to their goals, such as strengthening their feet or rehabilitation. Second, the learning process is easy: Unlike the SF-ex, the resistance object is easy to understand. Third, ankle joint movement is involved: unlike the SF-ex, both the intrinsic and extrinsic muscles of the foot can be trained. Finally, tube training is economical: Elastic tubes are relatively inexpensive. Athletes can easily carry them around with them, and they can be used at home or outdoors, without the need for any special equipment or machines. Tube training will provide athletes with a new option for training their IFMs.

4.3. Limitations and Future Research

This study has several limitations. First, the results of this study cannot be extended to women, other age groups, or athletes from different sports, as the participants were limited to healthy adult male university runners. Second, the relatively small sample size, the lack of a control group, and the fact that the study did not restrict normal running training mean that the results must be interpreted with caution. However, in research involving athletes, the sample size tends to be small because long-term observation is necessary [51]. Thirdly, because we recruited the runners of a university track and field club, selection bias cannot be denied. Finally, this study did not examine how these results affect the actual running performance. Despite the above-mentioned limitations, this study used a highly reliable method of randomized controlled trials, carefully evaluated the pre-intervention state, and conducted a longitudinal analysis. As a result, we were able to clearly show the effects of each exercise. This study suggests that toe tube training may improve the IFMs and their function. Incorporating toe tube training into daily training may be effective in preventing disability and promoting a return to play.

5. Conclusions

In this study, tube training increased the toe grip strength by 20.6%, toe gap strength by 18.7%, and RSI by 9.5%. Although no significant interaction was observed, the training effect was equivalent to or greater than that with SF-ex. This could be an effective alternative for runners who find SF-ex difficult and want to adjust the exercise load.