This study aimed to compare the foot muscle morphology and foot posture between healthy adults and lifesavers in sandy beach sports. The participants included 15 lifesaver athletes and 15 healthy adults. Using a non-contact three-dimensional foot measurement device, the foot length, width, and arch height of the right foot were measured while standing and sitting without back support, and the transverse arch length ratio and arch height index were subsequently calculated. Muscle cross-sectional area was measured using an ultrasound imaging device. Muscle cross-sectional areas, arch height, foot width, arch height index, and transverse arch length ratio were larger in the lifesaver than in the healthy adult group. Lifesavers had higher arches and more developed intrinsic and extrinsic muscles than healthy adults. Performing physical activity while barefoot on sandy beaches may effectively develop the foot intrinsic and extrinsic muscles and raise the arch.

Balance is important in lifesaving competitions. We aimed to investigate the relationship between dynamic balance and physical characteristics and functions in elite lifesavers by measuring the foot muscle cross-sectional area, ankle joint muscle strength, toe grasp strength, plantar superficial sensation, and dynamic balance (Y-balance test). In this observational study, we measured the foot muscle cross-sectional area, ankle dorsiflexion, plantar flexion, external flexion, isometric muscle strength, toe grasp strength, and superficial foot sensation of 15 adult lifesavers (12 males). The results show that toe grasp strength and ankle plantar flexion isometric muscle strength are particularly important for the dynamic balance of elite lifesavers working on sandy surfaces. Sand training improves intrinsic muscle strength and dynamic balance function. However, high training intensity may reduce plantar surface sensation; this needs to be verified through sand training interventions in the future.

Athletes need to enhance their foot function to improve their performance and prevent injuries and disability. Although foot function is believed to be improved by stabilizing the body on an unstable surface (e.g., a sandy beach), there have been no relevant studies to our knowledge. Here, we identified the differences in foot and balance functions between beach volleyball and volleyball players and investigated the effects of sandy surface training. We included six male beach volleyball players (BVB group) and six male volleyball players (VB group). The following six parameters were measured and compared between the groups: foot morphology, plantar surface perception, isometric ankle muscle strength, toe grip strength, static balance, and dynamic balance. The BVB group had significantly higher values in sensation perception, isometric ankle dorsiflexion muscle strength, and toe grip strength in the standing posture, with significant intrinsic foot muscle dominance, compared to the VB group. Playing barefoot increases the amount of tactile information received from the surface of the sole, which may lead to enhanced sensory perception by the foot. In addition, owing to the unstable sandy surface, the intrinsic muscles of the foot and lower leg may strengthen to maintain balance; therefore, training on a sandy surface may lead to improved foot and balance functions.

Medial tibial stress syndrome (MTSS) is an overuse injury characterized by pain along the posteromedial tibial border. This region contains several soft tissues, including adipose tissue and the tibialis posterior and flexor digitorum longus tendons. However, few studies have investigated whether these tissues exhibit abnormalities in MTSS. This study aimed to use MRI to evaluate abnormalities in the bone marrow or soft tissues of patients with MTSS and those with a history of medial tibial pain. Eighteen patients with MTSS, 20 uninjured athletes, and 17 individuals with a history of medial tibial pain underwent T1-weighted, T2-weighted, and short T1 inversion recovery imaging. The presence of bone marrow, periosteal, and peritendinous edema and abnormalities in the adipose tissue along the posteromedial tibial border were evaluated. Fisher's exact test was applied to determine the relationship between abnormalities and clinical status. Patients with MTSS exhibited abnormalities in the adipose tissue (27.3%), peritendinous edema (22.7%), bone marrow edema (22.7%), and periosteal edema (59.1%). However, the incidence of these abnormalities showed no statistically significant differences between the three groups. Athletes showed abnormalities in the bone marrow, periosteum or soft tissues, regardless of their clinical status. Various tissues, including the adipose tissue and peritendon along the posteromedial tibial border, may contribute to MTSS, highlighting its complex pathology. Imaging assessments are important for diagnosing MTSS and should complement physical examination and evaluation of the patient's history.

Balance is important in lifesaving competitions. We aimed to investigate the relationship between dynamic balance and physical function in elite lifesavers by measuring the foot muscle cross-sectional area, ankle joint muscle strength, toe grasp strength, plantar superficial sensation, and dynamic balance. In this observational study, we measured the foot muscle cross-sectional area, ankle dorsiflexion, plantar flexion, external flexion, isometric muscle strength, toe grasp strength, and superficial foot sensation of 15 adult lifesavers (12 males). The results showed that toe grasp strength and ankle plantar flexion isometric muscle strength are particularly important for the dynamic balance function of elite lifesavers working on sandy surfaces. Sand training improves intrinsic muscle training and dynamic balance function. However, high training intensity may cause a decrease in plantar surface sensation, which needs to be verified with sand training interventions in the future.