Characteristics of shoulder range of motion, muscle tightness, and streamlined body position in Japanese female para swimmers with unilateral forearm deficiency and in swimmers with vision impairment: a comparative cross-sectional study

Abstract

[Purpose] To compare the characteristics of shoulder range of motion (ROM), muscle tightness, and streamlined body position in female para swimmers with unilateral forearm deficiency (UFD) to those in swimmers with vision impairment (VI). [Participants and Methods] Female Japanese para swimmers with UFD (n=7) and VI (n=5) were included. Limb circumference, shoulder ROM, lower extremity muscle tightness, gross muscle strength, and streamlined body position were measured. [Results] The maximum upper arm circumference of the deficient arm and shoulder ROM for dominant and deficient flexion, deficient extension, and dominant and deficient external rotation were significantly lower in swimmers with UFD than in those with VI. [Conclusion] Female para swimmers with UFD are characterized by decreased ROM of the shoulder on the dominant and the deficient arms, quadriceps tightness, greater dominant grip strength, and compensated streamlined body position compared to swimmers with VI.

INTRODUCTION

Para swimmers with unilateral forearm deficiency (UFD), including congenital deficiency and acquired amputation, compete within sports class S9 because they have the same functional limitations¹⁾. They must swim without any prosthetic arm, following rules and regulations^{1, 2)}. Therefore, owing to their asymmetrical body structure and fluid force exertion, UDF swimmers may be exposed to localised stresses on their bodies by swimming using disability-specific strategies. Previous studies have indicated that stroke frequency is a significant determinant of front crawl performance in swimmers with UFD^{3, 4)}. This suggests that swimmers with UFD are required to produce propulsion using both arms with a high stroke frequency. Therefore, the unaffected arm may be exposed to more overload stress, leading to fatigue, as it is coordinated with the high-frequency strokes in the deficient/amputee arm.

Range of motion (ROM) of the shoulder can be limited by fatigue from swimming⁵⁾. Shoulder ROM limitation in swimmers leads to associated disorders such as shoulder pain, subacromial impingement, labral tears and nerve entrapment^{6, 7)}. Thus, decreased shoulder ROM in swimmers leads to pain and dysfunction of the shoulder complex, the so-called swimmer’s shoulder, which requires prevention and daily conditioning.

A streamlined body position reduces hydrodynamic drag, which is important for starts and turns in competitive swimming^{8, 9)}. The ideal streamlined body position⁸⁾ requires flexed shoulders and extended elbows and wrists, with the upper arms touching the sides of the head and the head is looking down. The feet are together, and the ankles are plantarflexed. For competitive swimmers, this requires adequate ROM of the joints and spine, whereas para swimmers have compensation for a streamlined body position owing to the restricted passive ROM and acquired disability, as shown in a previous study¹⁰⁾.

An understanding of the characteristics of functional status in para swimmers can facilitate the acquisition of their physical conditioning and sports-specific training. However, there is a lack of research investigating the physical characteristics of para swimmers. The purpose of this study was to clarify the characteristics of physique, static posture, and ROM of the shoulders in elite Japanese female para swimmers with UFD and compare them with swimmers with vison impairment (VI). Swimmers with VI were chosen as the comparison group due to the unavailability of able-bodied swimmers at elite level. Although swimmers with VI have no physical impairment in their limbs and were considered suitable for comparison, it is important to note that differences in the degree of visual impairment may influence the results. It is hypothesised that swimmers with UFD exhibit restricted ROM of the shoulder on the affected arm due to disuse and on the non-affected arm due to localised stress resulting from swimming training.

PARTICIPANTS AND METHODS

Seven female Japanese para swimmers with UFD (height 161.8 ± 3.5 cm, body mass 54.8 ± 2.9 kg, aged 17.7 ± 3.5 years, 6 with congenital deficiency, 1 with acquired amputation) and five with vision impairment (VI) (height 160.9 ± 4.0 cm, body mass 57.5 ± 6.2 kg, aged 23.0 ± 4.7 years, 2 blind swimmers, 3 with amblyopia) participated in this study. Height and weight were measured using a standard stadiometer and digital scale, respectively. Age and duration of disability were confirmed using the internal database of the Japanese Para Swimming Federation. Sports-specific training experience was self-reported by the participants. One participant with UFD had her forearm amputated at the age of three, and her functional impairment was determined to be the same as that of congenital UFD. As the participants in this study had a congenital forearm deficiency or acquired amputation, the short side of the forearm length was defined as the ‘deficient side’ and the healthy side as the ‘dominant side’ for convenience. According to the medical diagnostic form written by their primary medical doctor, none of the participants had any other psychosomatic functional or structural disease. All participants were engaged in competitive swimming at the national and/or international level and had been certified as either elite or youth swimmers by the Japanese Para Swimming Federation. We only included females in this study because none of the male swimmers with unilateral forearm deficiency was certified as elite or youth para swimmers by the Japanese Para Swimming Federation. Each swimmer had a different primary stroke and competed in multiple strokes.

The primary outcome of this study was shoulder ROM and the secondary outcomes included limb circumference, muscle tightness, gross muscle strength, and streamlined body position. The ROM of the shoulder was assessed for flexion, extension, external rotation at 90° of shoulder abduction and internal rotation at 90° of shoulder abduction. One physiotherapist was responsible for holding the upper extremity and checking compensatory movement, while the other conducted the measurements using a goniometer (GS11-002, OG Wellness Technologies Co., Ltd., Okayama, Japan) with a degree interval of one. The inter-rater reliability for goniometric measurements of passive shoulder ROM has been reported to be consistently high in previous studies^11,12,13), while highlighting the importance of standardized measurement techniques and suggesting that using the same examiner for repeated measurements may be beneficial to ensure reliability in clinical and research settings.

The heel-buttock distance (HBD) was measured to assess muscular flexibility, reflecting quadriceps femoris muscles¹⁴⁾. The HBD was measured using a measuring tape with the participant in a prone position with the knee bent passively. The passive straight leg raising (SLR) test was used to assess hamstring tightness. The SLR was measured at the end range of passive hip flexion with the knee straight in a supine position. Muscle tightness or resistance indicated full hip flexion, and flexion was achieved without pelvic tilt or knee bending¹⁵⁾. The measurements were taken once using the goniometer.

The maximum circumferences of both the upper arm and thigh were measured utilising a measuring tape with the participant in the supine position. The thigh circumference was measured at 5, 10, and 15 cm above the base of the patella. We measured limb circumference for two reasons: the possibility of low muscle mass on the deficient side and the possibility that muscles in lower limbs might be affected by the biomechanics of swimming⁴⁾, which is a whole-body movement.

Grip strength was evaluated in the relaxed standing position using a grip dynamometer (T.K.K.5401, Takei Scientific Instruments, Tokyo, Japan). The single-leg sit-to-stand test (SLSTST) was used to assess the gross muscle strength of the lower limb. The SLSTST was utilised to estimate the weight-bearing index (WBI), which can be calculated as the ratio of quadriceps strength (kg) to body mass (kg), as previously described in our study¹⁰⁾. The SLSTST procedure was conducted as follows: the participant was seated on a chair with a height of 40 cm, with the knee bent at an angle of 70°. The participant then removed one foot from the floor and stood on the other leg. Subsequent tests were conducted with chair heights of 30, 20, and 10 cm, respectively, for participants who had successfully completed the initial test. A physiotherapist always monitored the participant during the test. If compensatory movements (e.g. shifting the position of the grounded foot when standing up) were observed, the participant were immediately asked to stop the movement, and the record was invalidated.

All measurements were performed by two physiotherapists with a minimum of 16 years of clinical experience. The ROM, HBD, SLR, and circumferences were measured only once. The measurement for the grip strength and the SLSTST were performed twice and the maximum value was used for the analysis. Although blinding of assessors was not feasible due to the physical characteristics of the participants, standardized measurement protocols was implemented to minimize bias. Even though the measurements were taken during the competition season, none of the participants competed within three weeks of the measurement date.

The streamlined body position was qualitatively evaluated by observing digital photographs taken from the sagittal plane in a standing position while swimmers maintained their usual streamlined body positions.

Anthropometric and functional values were compared between the two groups (swimmers with UFD vs. swimmers with VI). The preliminary assessment of data normality was conducted through the implementation of the Shapiro–Wilk normality test. The difference in each variable between the swimmers with UFD and those with VI was compared using either an unpaired t-test or the Mann–Whitney U test, depending on the normality of the data. All comparisons were conducted using IBM SPSS Statistics version 24 (IBM Corp., Armonk, NY, USA), and statistical significance was defined as p<0.05. The streamlined body position of each participant was qualitatively assessed through observation and compared with the ideal streamlined body position as defined in previous studies^{8, 9)}. The similarities of the streamlined body position between the UFD and the VI were then extracted and the differences were compared by two physiotherapists with a minimum of 16 years of clinical experience. As there are no parameters available for the evaluation of the streamlined body position, the kinematic landmarks were utilised instead, including the curvature of the spine, the angle of the joints, and the positions of the body’s various segments.

Prior to undertaking the experimental procedures, all participants volunteered to participate in the study and provided written informed consent. For participants who were minors, written consent was obtained either from the parents or legal guardians. All study procedures were approved by the relevant institutional review board of the institution to which the authors belong (Approval Number: 21-15) and were conducted in accordance with the tenets of the Declaration of Helsinki.

RESULTS

The participants’ basic characteristics are shown in Table 1. A comparison of the basic characteristics of the participants between the groups showed that the mean age of swimmers with UFD was significantly lower than that of swimmers with VI (p<0.05).

Table 1. Basic characteristics of the swimmers with UFD and with VI.

	UFD (n=7)	VI (n=5)
Height (cm)	161.8 ± 3.5	160.9 ± 4.0
Body mass (kg)	54.8 ± 2.9	57.5 ± 6.2
Age (years)*	17.7 ± 3.5	23.0 ± 4.7
Duration of disability (years)	17.1 ± 4.4	15.6 ± 12.0
Sports specific training experience (years)	9.0 ± 3.1	11.8 ± 7.1

Mean ± SD. *p<0.05 t-test for unpaired samples. UFD: unilateral forearm deficiency; VI: vision impairment.

Shoulder ROM, HBD, SLR, SLSTST, and grip strength are shown in Table 2. Swimmers with UFD had significantly smaller shoulder ROM than that of swimmers with VI; for flexion in both dominant (UFD 180.0 ± 13.8° vs. VI 197.8 ± 4.4°, p<0.05) and deficient/non-dominant side (170.1 ± 6.4° vs. 194.2 ± 6.6°, p<0.001), for an extension on deficient/non-dominant side (57.3 ± 13.9° vs. 79.2 ± 13.3°, p<0.05) and for external rotation on both dominant (97.6 ± 11.1° vs. 120.0 ± 17.1°, p<0.05) and deficient/non-dominant side (85.7 ± 15.6° vs. 116.2 ± 16.7°, p<0.05), reporting the large effect size.

Table 2. The maximum upper arm circumference and the maximum thigh circumference of the swimmers with UFD and with VI.

	UFD (n=7)	VI (n=5)	Means difference	ES
	(mean ± SD)	(mean ± SD)	(95% CI)
Maximum upper arm circumference (cm)
Dominant	27.3 ± 3.1	30.4 ± 2.0	1.6 (−6.6 to 0.4)	−1.14
Non-dominant/deficient	23.8 ± 3.7*	30.1 ± 1.8	1.8 (−10.2 to −2.3)	−2.05
Thigh circumference (cm)
5 cm from the base of the patella
Dominant	39.8 ± 1.9	39.0 ± 3.0	1.4 (−2.3 to 3.9)	0.33
Non-dominant/deficient	40.4 ± 2.2	38.9 ± 3.1	1.5 (−1.9 to 4.9)	0.59
10 cm from the base of the patella
Dominant	44.7 ± 4.4	44.3 ± 3.1	1.3 (−2.6 to 3.4)	0.17
Non-dominant/deficient	45.1 ± 2.5	44.2 ± 2.9	1.6 (−2.5 to 4.4)	0.36
15 cm from the base of the patella
Dominant	49.3 ± 2.5	49.5 ± 2.2	1.4 (−1.9 to 2.9)	−0.07
Non-dominant/deficient	50.0 ± 2.2	49.4 ± 2.6	1.4 (−2.5 to 3.7)	0.24

*p<0.05 t-test for unpaired samples.

UFD: unilateral forearm deficiency; VI: vision impairment; ES: Cohen’s d effect sizes.

Swimmers with UFD had significantly greater HBD on the non-dominant side (UFD 8.6 ± 2.2 cm vs. VI 3.6 ± 4.1 cm, p=0.022) than that of swimmers with VI while no difference was observed on the dominant side between groups.

There were no differences in the SLR and SLSTST values on either the dominant or non-dominant sides between the groups.

Dominant grip strength in swimmers with UFD was 31.2 ± 2.4 kg (mean ± SD) which was significantly greater than that in swimmers with VI of 27.9 ± 1.9 kg (p<0.05).

The maximum upper arm and thigh circumferences are listed in Table 3. Maximum upper arm circumferences in swimmers with UFD were 27.3 ± 3.1 cm/23.8 ± 3.7 cm (mean ± SD, dominant/deficient) which was significantly smaller than that in swimmers with VI of 30.4 ± 2.0 cm/30.1 ± 2.8 cm, reporting the large effect size. No difference was observed in thigh circumference between the groups in the three thigh positions in both dominant and deficient/non-dominant limbs.

Table 3. Shoulder ROM, lower limb flexibility, and gross muscle strength of the swimmers with UFD and VI.

		UFD (n=7)	VI (n=5)	Mean difference	ES
		(mean ± SD)	(mean ± SD)	(95% CI)
Shoulder ROM (degrees)
Flexion	Dominant	180.0 ± 13.8*	197.8 ± 4.4	6.5 (−32.2 to −3.4)	−1.62
	Non-dominant/deficient	170.1 ± 6.4**	194.2 ± 6.6	3.8 (−32.5 to −15.6)	−3.71
Extension	Dominant	68.0 ± 19.0	76.0 ± 24.0	12.5 (−35.9 to 19.9)	−0.37
	Non-dominant/deficient	57.3 ± 13.9*	79.2 ± 13.3	8.0 (−39.7 to −9.5)	−1.61
External rotation	Dominant	97.6 ± 11.1*	120.0 ± 17.1	8.1 (−40.5 to −4.4)	−1.62
	Non-dominant/deficient	85.7 ± 15.6*	116.2 ± 16.7	9.5 (−51.5 to −9.5)	−1.90
Internal rotation	Dominant†	52.9 ± 9.3	68.8 ± 19.6	n/a	n/a
	Non-dominant/deficient	48.0 ± 18.8	64.8 ± 13.2	9.8 (−38.7 to 5.1)	−1.00
Heel–buttock distance (cm)	Dominant	7.3 ± 1.7	3.7 ± 4.3	n/a	n/a
	Non-dominant/deficient	8.6 ± 2.2*	3.6 ± 4.1	1.8 (0.9 to 9.0)	1.59
Straight leg raising (degrees)	Dominant	81.3 ± 13.5	93.4 ± 12.2	7.6 (−29.0 to 4.8)	−0.93
	Non-dominant/deficient	87.3 ± 12.0	89.6 ± 13.3	7.3 (−18.7 to 14.0)	−0.19
Single leg sit to stand test (cm)	Dominant†	14.2 ± 11.3	18.0 ± 16.4	n/a	n/a
	Non-dominant/deficient†	4.2 ± 5.3	18.0 ± 16.4	n/a	n/a
Grip strength (kg)	Dominant	31.2 ± 2.4*	27.9 ± 1.9	1.3 (−28.5 to 6.2)	1.48
	Non-dominant/deficient	n/a	n/a	n/a	n/a

*p<0.05 t-test for unpaired samples, **p<0.001 t-test for unpaired samples, ^†As the variables were not normally distributed, the Mann–Whitney U test was used. UFD: unilateral forearm deficiency; VI: vision impairment; ES: Cohen’s d effect sizes; ROM: range of motion; n/a: not applicable.

The streamlined body positions of the swimmers in the standing position from the sagittal view are shown in Fig. 1. Qualitative assessment of the streamlined body position showed inadequate shoulder flexion on both the dominant and deficient sides in most swimmers with UFD compared to swimmers with VI. In addition, most swimmers with UFD showed an excessive lumbar lordosis angle, whereas it was observed in only swimmer J among swimmers with VI.

Fig. 1.

Streamlined body position of swimmers with UFD and with VI (Black arrows indicate the deficient shoulder joints of the participants).

UFD: unilateral forearm deficiency; VI: vision impairment.

DISCUSSION

To our knowledge, this is the first study to describe the functional characteristics of swimmers with UFD. Shoulder ROM was significantly reduced in swimmers with UFD compared to those with VI, particularly for flexion, extension, and external rotation on both the dominant and deficient sides. The maximum upper arm circumference of the deficient side was significantly smaller in swimmers with UFD than in those with VI on the non-dominant side. All participants had elbow joints, and the distal end of the deficient limb had no fingers, making grasping movements impossible and infrequent in daily life. This likely results in muscle atrophy in the upper arm muscle group.

Shoulder is a value, which can be used to characterise swimmers with UFD. The ROM for deficient shoulder flexion, extension, and external rotation of swimmers with UFD was significantly smaller than that observed on the non-dominant side of swimmers with VI. This result suggests that activities such as hanging are difficult to perform because of the deficient part distal to the forearm. Congenital limb deficiency which was diagnosed in six swimmers with UFD in this study, is a rare disease that affects appearance and daily life. According to a recent nationwide epidemiological study, the estimated prevalence of congenital upper limb deficiencies in Japan was 3.39 per 10,000 live births¹⁶⁾. Swimmers with congenital UFD have few opportunities to use their deficient upper limbs in daily life during development. Previous studies have shown that in Japan, children with congenital unilateral upper limb deficiency are not prescribed or do not use prosthetic hands even though they need them because of their functional impairment^{17, 18)}. James et al.¹⁹⁾ reported that prostheses neither improved the function nor quality of life in children with congenital UFD. This is because many of them can complete their daily activities without using a prosthetic hand.

Restricted shoulder ROM is a parameter that characterizes body function in swimmers with UFD. The hypothesis was that swimmers with UFD would demonstrate restricted shoulder ROM on the deficient arm because of disuse and on the unaffected arm due to an increased training load in swimming. The result showed that shoulder ROM for deficient flexion, extension, and external rotation was significantly smaller in swimmers with UFD than in those with VI. Furthermore, the ROM for dominant shoulder flexion and external rotation in UFD swimmers was markedly reduced as compared to that of the dominant side in swimmers with VI. The reason for the smaller ROM of flexion and external rotation of the shoulder joint on the dominant side may be its asymmetrical body structure and fluid force exertion, which creates a local load on the body by swimming with a disability-specific strategy and increases the stroke frequency on the deficient side. In front crawl swimming, shoulder joint motion on the affected side of top-level UFD swimmers has been reported to be dominated by extension rather than adduction movements²⁰⁾. It can be assumed that the angular velocity of the shoulder joint on the deficient side is higher because of the high stroke frequency caused by the short lever arm, although the generation of propulsive forces by the deficient upper limb is lower. Therefore, the load on the shoulder flexor muscles of the affected side may be higher. During submerged gliding in simultaneous swimming techniques such as breaststroke and butterfly, the long axis of the body is considered to roll towards the sound side because of the deficient arm⁴⁾. Additionally, a healthy upper limb must be used to levitate the body for breathing. Therefore, to keep the body parallel to the water surface, UFD swimmers need to use the upper limbs to generate non-propulsive fluid forces to levitate the body, which tends to place an excessive load on the healthy side. The deficient upper limb does not have a segment that exerts large fluid forces on the hand and forearm and, therefore, generates little or no force in the other directions of propulsion. This is thought to lead to increased fatigue and shortening of primary muscles such as the latissimus dorsi to produce propulsive forces underwater. The latissimus dorsi muscle is primarily responsible for the extension, adduction, and internal rotation of the upper extremities, thereby contributing to the forward propulsive force during front crawl swimming²¹⁾. Repetitive swimming training likely causes in increased muscle stiffness and resistance to elongation, resulting in restricted ROM during shoulder flexion²²⁾. This may trigger restricted ROM during shoulder flexion and external rotation, leading to excessive lumbar lordosis in the streamlined body position owing to postural compensation.

Given that the latissimus dorsi attaches to the iliac crest at its origin, contraction causes the pelvis to tilt anteriorly.

This result is reflected in the characteristics of the streamlined body position, as shown in Fig. 1. Qualitative analysis of the streamlined body position in the sagittal plane by observation showed that all swimmers, except swimmer A, had insufficient shoulder joint flexion on the deficient side and excessive lumbar lordosis. However, the streamlined body posture of swimmers with VI showed that swimmer J had excessive lumbar kyphosis, but the other swimmers did not exhibit inadequate shoulder joint flexion, as observed in swimmers with UFD. This result may be explained by the fact that swimmers with UFD had significantly greater HBD values. Increased HBD values indicate that the muscle group from the hip to the front of the thigh was shortened and/or tightened. Some muscle groups tilt the pelvis forward and increase lumbar lordosis, which is thought to cause streamlined postural irregularities. Zwierzchowska et al.²³⁾ reported that the internal compensatory mechanisms for the original functional impairment occurred as structural changes in the spinal curvature and thoracic and lumbar spine ROM in Polish elite para swimmers. In such circumstances, it is evident that compensatory mechanisms are activated, particularly among those who are mobility impaired. In these cases, the normal functioning of the musculoskeletal system may be compromised owing to congenital or acquired dysfunction²⁴⁾. In the present study, limited shoulder joint ROM and quadriceps stiffness may have caused an uneven streamlined body position through internal compensatory mechanisms. An asymmetrical body structure and excessive load on the affected lower limb due to fluid force exertion may contribute to quadriceps stiffness. In front crawl swimming, the timing of the lower limb kick and forearm deficiency causes a greater role to the deficient side⁴⁾; however, the deficient side generates less or no buoyancy or non-propulsive force required for rollback compared to the sound side²⁵⁾. The kicking action in crawl swimming is responsible for lifting the lower limb in the direction of pitch rotation by vertical upward force generation²⁶⁾. In UDF swimmers the greater force generation from the kicking action on the affected side may assist the rollback of the affected side. Therefore, it is possible that there was excessive loading on the affected lower limb, and that the HBD values of the affected lower limb were significantly greater in forearm-deficient swimmers than in visually impaired swimmers. The results also support this possibility, as the mean SLSTST values of the UFD swimmers were larger on the deficient side, although a statistical analysis was not conducted to identify side-to-side differences.

The final point of interest in this study was the group differences in the grip strength of the dominant hand. The dominant handgrip strength of the patients with UFD was significantly higher than that of the patients with visual impairment. The reasons for this are difficult to explain based on the results of this study. However, there are two possibilities. The first possibility is that people with missing forearms have stronger grip strength on the healthy side because they perform activities of daily living using only one hand. The second possibility is that those with VI perform fewer grasping movements in their daily activities, because holding heavy objects poses a risk of injury.

However, the present study has some limitations. First, it may prove challenging to describe the general characteristics of competitive swimmers with UFD, given that only seven female swimmers were included in this study. The sample size was insufficient for statistical analysis. If the difference in the main outcome of shoulder ROM between the two groups was assumed to be 10° with a standard deviation of 7° and a power of 80% based on the values obtained in our previous preliminary studies which is not published, the number of cases required was calculated to be 8 in each group. Furthermore, this study included both congenital and acquired UFD swimmers may introduce heterogeneity in the sample, as congenital and acquired limb deficiencies could have distinct functional and biomechanical implications. In addition, the primary stroke of the swimmers in this study was different and they competed in different strokes. Therefore, a causal relationship between daily training and joint ROM could not be established. Nevertheless, the number of competitive swimmers with UFD is relatively limited, thus underscoring the need for a larger sample size in future case-control studies to provide more robust evidence. Secondly, this was a cross-sectional study. ROM can be affected by fatigue⁵⁾, which can influence the accuracy of measurements taken. Therefore, it is important to consider the volume of swimming training and the timing of measurements when assessing ROM and flexibility; however, the training load was not assessed in this study. In relation to the evaluation methods employed, the present study examined the streamlined body position on land. Nevertheless, it is important to acknowledge the study’s inability to ascertain whether this position truly reflects the streamlined body position in an underwater context, which constitutes a significant limitation. Third, the study included swimmers with vision impairment as control participants, to compare the physical characteristics of these individuals with those of swimmers with UFD. Although swimmers with VI did not display any physical impairments in their extremities, their physical characteristics may differ from those of their able-bodied swimmers. Furthermore, this study combines blind swimmers and swimmers with amblyopia, but existing literature indicates that performance and physical characteristics differ based on the degree of visual impairment²⁷⁾. This grouping lacks justification and could obscure potential differences in shoulder ROM and other outcomes.

As conclusions, we found that female para swimmers with UFD are characterised by decreased shoulder on both dominant and deficient arms, quadriceps tightness, greater dominant grip strength, and compensated streamlined body position compared with swimmers with VI. These findings suggest that conditioning programs and swim training based on the physical characteristics of swimmers with UFD may be effective in improving athletic performance and preventing sports injuries.

Funding

This work was supported by JSPS KAKENHI Grant Number JP22K17715.

Conflict of interests

None declared.