Background: Core stability exercises are widely applied in rehabilitation and training programs, but evidence regarding the effects of activation strategies and surface conditions on abdominal muscle recruitment during plank exercise remains inconsistent. Objects: This study aimed to investigate how different activation strategies (hollowing vs. bracing) and surface conditions (stable vs. unstable) influence selective activation of abdominal muscles during the plank exercise. Methods: Thirty-six healthy male adults in their 20s participated. Ultrasound imaging was used to measure the relative thickness of the transversus abdominis (TrA), internal oblique (IO), and external oblique (EO) under four randomized conditions: stable-hollowing, stable-bracing, unstable-hollowing, and unstable-bracing. Relative thickness was calculated as [(contraction – rest) ÷ rest] × 100. Data were analyzed using three-way repeated-measures ANOVA with Bonferroni comparison. Results: No significant three-way interaction was found (p = 0.840). However, a significant muscle × surface interaction indicated that TrA thickness increased more on a stable surface (p < 0.05), while IO and EO showed no difference. A significant muscle × strategy interaction revealed that hollowing induced greater relative thickness in all muscles, particularly in TrA, compared with bracing (p < 0.001). No significant strategy × surface interaction was observed (p = 0.512). Conclusion: Abdominal hollowing and a stable surface independently enhanced TrA thickness during plank exercise. These findings suggest that stable-surface plank exercise with hollowing is an effective strategy for selectively recruiting deep abdominal muscles, providing practical implications for clinical and sports settings. These findings may be specific to anklesling– induced instability and may not extend to other types of unstable surfaces.

Background: Falls represent a critical public health issue involving neuromuscular control strategies to execute appropriate motor plans. While self-initiated falls (SIF) and motor-induced falls (MIF) are common laboratory paradigms, the continuous temporal differences in their underlying neuromuscular strategies remain poorly understood. Objects: We conducted experiments to identify and compare the neuromuscular control strategies between SIF and MIF across three directions using continuous waveform analysis. Methods: Eight healthy young adults performed SIF and MIF in forward, backward, and sideways directions while surface electromyography was recorded from the bilateral tibialis anterior (TA), lateral gastrocnemius, and medial gastrocnemius. Data were normalized via maximum voluntary isometric contraction and reference voluntary contraction and analyzed using statistical non-parametric mapping over the entire fall duration (0%–100%). Results: Neuromuscular divergence was strategically concentrated within three critical windows: initial, mid-to-terminal, and terminal phases. For the TA, MIF elicited significantly higher activation during the initial phase of sideways falls (1%–5%, p < 0.05) and the mid-to-terminal phase of backward falls (62%–75%, p < 0.05). For the GCM, significantly higher activation in MIF was observed during the terminal phase of forward falls (70%–99%, p < 0.05), both early (1%–24%, p < 0.05), and late (58%–98%, p < 0.05) phases of sideways falls, and the initial response phase of backward falls (1%–5%, p < 0.05). Conclusion: The central nervous system is characterized by high-amplitude activation patterns, which may reflect a response to unpredictable threats (MIF) compared to planned descents (SIF). These findings suggest the potential importance of direction-specific and timesensitive neuromuscular training to better prepare for real-world falls.

Background: Pressure biofeedback may facilitate selective rotator cuff activation during shoulder external rotation, but training effects and structural changes are unclear. Objectives: To examine the effects of a 4-week external rotation program with pressure biofeedback on shoulder muscle activity and rotator cuff thickness. Design: Quasi-experimental design. Methods: Thirty healthy adults were randomized to experimental (n=15) or control (n=15). Both performed seated external rotation at 30° with an elastic band (3×12 reps, 4 sessions/week, 4-week); the biofeedback group maintained 40 mmHg scapular adduction pressure. Surface EMG (%MVIC) and ultrasound muscle thickness were assessed pre/post. Paired and independent t-tests were used (α=.05). Results: In the experimental group, teres minor and infraspinatus activity increased, whereas middle and posterior deltoid activity decreased (P<.05). Post-intervention, rotator cuff activity was higher and posterior deltoid activity was lower versus control (P<.05). Muscle thickness showed no significant changes. Conclusions: A 4-week pressure biofeedback training program changed muscle activation during shoulder external rotation by increasing rotator cuff activation and decreasing compensatory deltoid activity. These findings indicate meaningful neuromuscular adaptations during the external rotation task.

Background: Grip strength is a widely accepted clinical indicator of upper limb function. The grip strength measurement validity and clinical relevance of the American Society of Hand Therapists (ASHT) and suboptimal postures, such as slumped sitting, remain unclear. Objects: This study aimed to investigate whether sitting postures, including slumped posture, influence grip strength and upper limb muscle activation and to determine the clinical significance of grip strength assessment in the slumped position. Methods: Forty healthy adult males participated in a cross-over design study. Grip strength and surface electromyography of the triceps brachii, biceps brachii, anterior deltoid, and upper trapezius were measured in ASHT-recommended, slumped, and self-balanced postures. The Friedman test was used to compare outcomes across postures, and the relationship between grip strength and muscle activation was determined using Pearson correlation. Results: Grip strength significantly differed across postures (χ² = 25.37, p < 0.001), with ASHT posture having the highest values and slumped posture the lowest. Triceps brachii and upper trapezius showed significant variations in muscle activity across postures (p < 0.05). The electromyography-to-force ratio, representing neuromuscular efficiency, was the highest in ASHT posture. Grip strength strongly correlated with triceps brachii activity (r = 0.72, p < 0.001). Conclusion: Postural alignment significantly affects grip strength and upper limb muscle efficiency. These results highlight the clinical relevance that grip strength assessment should consider both ideal and habitual postures to improve the validity of functional evaluation and rehabilitation planning.

Background: Passive or therapist-assisted stretching, followed by scapular stabilization exercises, has been shown to be effective. However, most previous studies have focused on stretching individual muscles or specific movement directions, often neglecting the role of active scapular stretching. Objects: This study aimed to compare changes in the muscle activity of the lower trapezius (LT), serratus anterior (SA), and upper trapezius (UT), as well as the scapular posterior tilt (SPT) angle before and after scapular circle (SC) stretching during SPT exercise. Methods: Twenty participants were recruited for this study. Electromyography electrodes were attached to the LT, SA, and UT. Muscle activity and the posterior scapular tilt angle were measured while performing the SPT exercises. After the SC stretch, the measurements were repeated in the same manner. The LT, SA, and UT electromyography activities and SPT angles were analyzed using paired t-tests. Results: LT activity was significantly higher in the SC stretch plus SPT exercise compared with in the SPT exercise alone (p = 0.018). There were no significant differences in SA activity between the SPT and SC stretch plus SPT exercise conditions (p = 0.812). UT activity significantly increased in the SC stretch plus SPT exercise compared with that in the SPT exercise (p = 0.001). The SPT angle was significantly enhanced during SPT exercise after the SC stretching compared to that without SC stretching (p = 0.009). The RSP improved by 2.32% compared to the initial posture when only the SPT was performed, and improved by 9.95% when the SPT was performed after the SC stretching. Conclusion: These results suggest that performing SC stretching prior to SPT exercise may effectively improve scapular alignment and posture, even when UT activation increases more than of the LT. Elevated UT activity highlights the need to address muscular balance in corrective exercise design.

Background: During daily activities, stability is maintained to enhance the function of muscles surrounding the lumbopelvic and hip structures. The core muscles such as the rectus abdominis (RA), external oblique (EO), and internal oblique (IO) responsible for this stability. One effective static exercise for strengthening these muscles is the plank. Objects: This study aimed to compare abdominal electromyographic activation when an unstable support surface was applied to the upper and lower extremities during a standard and a knee plank. Methods: A total of 30 adults (15 males and 15 females) participated in this study. Surface electromyography electrodes were placed on the RA, EO, and IO muscles. Data were collected under six conditions for males, including two plank postures (standard and knee planks) and three unstable surface conditions (a dynamic balance cushion applied to the upper extremities, lower extremities, or no cushion). Female participants performed only the knee plank. A mixed-effects model with a random intercept was used to analyze muscle activation across plank posture and surface position, with statistical significance set at α = 0.05. Results: In males, the standard plank elicited greater muscle activation than the knee plank across all muscles (p < 0.0001). Additionally, applying an unstable support surface to the upper extremities significantly increased muscle activation in both plank postures in EO and IO (p < 0.001). Other muscle, RA, was only affected by the unstable support surface in the standard plank position only. In females, the knee plank with upper limb instability resulted in the highest muscle activation for all muscles. Conclusion: These findings highlight the importance of surface instability in core muscle engagement. However, future studies should further investigate abdominal muscle activation with a more detailed analysis and the inclusion of a control group to enhance comparative validity.

Background: Portable, small computers and smartphones are now considered essential tools in modern society and smartphone ownership and usage rates are rising every year. However, excessive smartphone use can have musculoskeletal and postural implications, leading to “smartphone addiction” and related dysfunctions. Objects: This study aimed to investigate the effects of smartphone addiction on scapular position and muscle activity during shoulder abduction in asymptomatic individuals. Methods: A total of 45 participants were classified into high-risk, middle-risk, and low-risk groups based on their smartphone addiction levels. Scapular position was measured using the scapular index, round shoulder posture (RSP), lateral scapular slide test, and scapulohumeral rhythm spine angle. Muscle activity was assessed using electromyography of the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and anterior deltoid (AD) muscles during shoulder abduction. Results: Smartphone addiction was significantly associated with altered scapular position and muscle activity. The high-risk group exhibited greater forward head posture and more pronounced RSP. Additionally, the high-risk group had lower SA activation and higher UT, LT, and AD muscle activity, indicating compensatory mechanisms due to altered scapular positioning. Conclusion: These findings suggest that excessive smartphone use contributes to postural deviations and altered muscle activation patterns, which may lead to musculoskeletal dysfunction over time. Clinicians should consider smartphone use when assessing patients with scapular dysfunction, and future studies should explore interventions to mitigate these effects.

Background: Prolonged use of computers and mobile devices has contributed to postural abnormalities such as Rounded Shoulder Posture (RSP), which is characterized by muscle imbalances that can lead to pain and functional limitations. Correcting these imbalances through targeted stretching and strengthening exercises was expected to help improve postural alignment and muscle function. Objectives: This study aimed to investigate the effects of a six-week integrated exercise program targeting the pectoralis minor (PM), upper trapezius (UT), and lower trapezius (LT) on postural alignment and muscle activation in female adults with RSP. Design: Single-group pre-post test study. Methods: Eighteen female university students (aged 20–22 years) with RSP participated in a six-week intervention consisting of PM stretching, UT stretching, and LT strengthening exercises. RSP severity was assessed using acromion-to-ground distance, PM length was measured with a caliper, and surface electromyography (sEMG) was used to evaluate UT and LT muscle activity. Normality was verified using the Shapiro-Wilk test, and paired t-tests were conducted for statistical analysis (α=0.05). Results: After the intervention, significant improvements were observed in all measured variables. Acromion-to-ground distance decreased (P<0.001), PM length increased (P<0.001), UT activation decreased (P<0.01), and LT activation increased (P<0.01). Conclusion: The six-week integrated exercise program effectively improved postural alignment and muscle activation in women with RSP by addressing muscle shortening, overactivity, and weakness. These findings suggest that combined stretching and strengthening exercises can serve as a practical and effective approach for RSP correction. Future studies with longer durations and diverse populations are recommended to further validate these results and enhance clinical applicability.

Background: The plank exercise is widely used in rehabilitation to enhance core muscle activation, spinal stability, and reduce the risk of lower back injuries. Objectives: This study investigated the effects of exercise complexity and instability on core muscle activation, with a particular focus on using a sling suspension system during prone bridge exercises. Design: Cross-sectional study. Methods: Twenty healthy adults performed three variations of prone bridge exercises: Both Limb Prone Bridge (BLPB), Single Limb Prone Bridge (SLPB), and Single Limb Prone Bridge with Hip Abduction (SLPBHA). Electromyography (EMG) was used to measure muscle activation in the erector spinae (ES), multifidus (MF), and internal oblique (IO) muscles. Results: Significant increases in ES muscle activation were observed during SLPBHA compared to BLPB and SLPB (P<.05), indicating that exercise complexity and the introduction of instability significantly enhanced ES activation. However, no significant differences were found in MF and IO activation across the exercise variations (P>.05). Conclusion: This study underscores the importance of exercise complexity and instability, particularly SLPBHA, in enhancing ES muscle activation. The findings support the inclusion of these exercises in core stability training programs aimed at improving spinal stability and preventing lower back injuries.

Background: The peroneus longus (PL) and peroneus brevis (PB) function as the primary muscles of eversion, a movement closely associated with tibial external rotation for ankle mortise stability. Ankle motion and tibial rotation vary based on different ankle and knee positions. Objects: This study aimed to investigate the PL, PB, and biceps femoris (BF) muscle activation and eversion strength during side-lying isometric eversion exercise based on different ankle positions (neutral [N] and plantarflexion [PF]) and knee positions (90° flexion [KF] and extension [KE]). Methods: Thirty healthy adults with an Ankle Joint Functional Assessment Tool score of ≥ 22 were recruited (mean age = 24.8 ± 3.1 years). Maximal isometric eversion strength and submaximal muscle activation of the PL, PB and BF were measured during isometric eversion exercise in side-lying. A 2 × 2 repeated measures analysis of variance was performed to investigate differences in muscle activation and strength. Results: The PL and PB muscle activation showed significant main effects with the knee and ankle positions (p < 0.05); activation was greater in the KE and PF positions than in the KF and N positions. The BF muscle activation showed a significant interaction effect with knee and ankle positions, which was greater in knee extension and ankle plantarflexed (KEPF) position than in knee flexion and ankle plantarflexed (KFPF) position (p < 0.05). Eversion strength showed a significant main effect only in ankle position (p < 0.05) and was greater in the N position than in the PF position. Conclusion: The results of this study indicate that the KEPF position can be recommended to facilitate contraction of the PL and PB during side-lying eversion exercise. Furthermore, the effects of the knee-ankle positions should be considered for measuring ankle eversion strength and implementing the isometric submaximal side-lying eversion exercise.

Background: Lateral instability of the ankle is one of the most common causes of musculoskeletal ankle injuries. The peroneus longus (PL) and peroneus brevis (PB) contribute to ankle stability. In early rehabilitation, isometric exercises have been selected for improvement of ankle stability. To effectively train the peroneal muscles during eversion, it is important to consider ankle and body posture. Objects: This study aimed to compare activation of the PL, PB, and biceps femoris (BF) muscles during eversion in different ankle postures (neutral [N], plantarflexed [PF]) and body postures (sitting and side-lying). Methods: Thirty healthy individuals with no history of lateral ankle sprains within the last 6 months were included in the study. Maximal isometric strength of eversion and muscle activation were measured simultaneously. Muscle activation at submaximal eversion was divided by the highest value obtained from maximal isometric eversion among the four postures (percent maximal voluntary isometric contraction [%MVIC]). To examine the differences in muscle activation depending on posture, a 2 × 2 repeated measures analysis of variance (ANOVA) was conducted. Results: There were significant interaction effects of ankle and body postures on PL muscle activation and evertor strength (p < 0.05). The PL muscle activation showed a significantly greater difference in the side-lying and PF conditions than in the sitting and N conditions (p < 0.05). Evertor strength was greater in the N compared to the PF condition regardless of body posture (p < 0.05). In the case of PB and BF muscle activation, only the main effects of ankle and body posture were observed (p < 0.05). Conclusion: Among the four postures, the side-lying-PF posture produced the highest muscle activation. The side-lying-PF posture may be preferred for effective peroneal muscle exercises, even when considering the BF muscle.

Background: Using wearable passive back-support exoskeletons in workplace has attracted attention as devices that support the posture of workers, enhance their physical capabilities, and reduce physical risk factors. Objects: This study aimed to investigate the effect of a wearable passive back-support exoskeleton on the activity of the erector spinae muscles during lifting tasks at various heights. Methods: Twenty healthy adult males were selected as subjects. Electromyography (EMG) was used to assess the activity of the erector spinae muscles while performing lifting tasks at three distinct heights (30, 40, and 50 cm), with and without the application of the Wearable Passive Back Support Exoskeleton. EMG data were gathered before and after the application of the orthosis. Results: The use of the Wearable Passive Back Support Exoskeleton resulted in a significant decrease in muscle activity when lifting a 10 kg object from heights of 30 and 40 cm (p < 0.05). Additionally, there was a significant reduction in muscle activity when lifting from a height of 50 cm compared with that at lower heights (p < 0.05). Conclusion: The use of a wearable passive back-support exoskeleton led to a decrease in the activity of the erector spinae muscles during lifting tasks, irrespective of the object's height. Our results suggest that the orthosis we tested may help decrease risk of lower back injuries during lifting.

본 연구는 EMG(electromyography) 텍스타일 전극 개발을 목적으로 레이어 수의 디자인 및 원단을 다르게 하여 성능 및 신호 획득 안정성을 평가한다. 레이징 및 프레스 공정을 통하여 텍스타일 전극을 제조하며 Layer-0, Layer-1, Layer-2로 레이어 유무 및 수에 따른 결과를 분석했다. 이에 레이어 유무에 따라서는 근활성 측정에 영향을, 수가 많을수록 높은 성능이 나타남을 확인할 수 있었다. Layer-2 구조로 통일하여 5가지의 원단(네오프렌, 스판덱스 쿠션, 폴리에스테르 100%, 나일론 스판덱스, 광목 캔버스)으로 전극을 제조해 실험해 보았다. 성능적인 면에서, 원단의 중 량이 높은 나일론 스판덱스가 높은 성능을 보였으며, 스판쿠션 텍스타일 전극이 근활성도 수득에 높은 안정성을 보 였다. 이에 위 연구는 레이어에 따른 성능 연관성과 전극-피부사이의 닿는 면적 간의 관계 등을 고찰하여 슬리브 전체의 의복압을 늘리는 대신 특정 센서 측정 부위에만 높은 압력을 가함으로 차후 연구에서 레이어의 수 및 물성에 따른 전극의 공학적 설계 가능성을 제시한 의의가 있다.

Background: As ways to optimize the mobilization of postural stability muscles for sitting up motions, arm reaching motions and head raising motions have important effects. Objectives: This study was conducted to investigate the effects of reaching to sit-up training on the trunk muscle activity, postural ability, and balance ability of patients with hemiplegia due to stroke. Design: Randomized controlled trial. Methods: This study was conducted with 18 stroke patients who met the selection criteria divided into two groups: a study group of 9 patents and a control group of 9 patients. The study group carried out reaching to sit-up training, which can promote trunk muscles and improve control through trunk interactions. The control group received general physical therapy intervention Results: The activity of the trunk muscle was significantly different before and after intervention in study and control group. The functional reaching test showed significant changes in both the study group and the control group. The timed up and go test showed a significant change in the study group. Conclusion: Reaching to sit-up training for 4 weeks showed increases in trunk muscle activity in stroke patients and was effective in improving balance ability.

Background: A decrease in physical activity has been observed due to the global pandemic, resulting in the onset and progression of musculoskeletal disorders as chronic diseases. Objectives: This study aimed to assess the difference in the degree of contraction of the lower limb muscles between the existing vertical vibration method and a new cross-vibration method. Design: Randomized controlled trial. Methods: The exercise program using whole-body vibration equipment was conducted for 12 sessions, 25 min per session, three times per week for 4 weeks. Results: The changes over time showed a significant difference in cross-alternating vibrations (P<.05), except for the lateral gastrocnemius and tibialis anterior, with no significant difference in sonic vertical vibration (P>.05). The interaction between time and group was significant for all muscles (P<.05), except for the biceps femoris, with differences between before the program and at 2 and 4 weeks after the program revealed in the post-hoc analysis. Conclusion: Future studies should further evaluate the use of CAV exercise devices as auxiliary equipment in exercise by assessing different groups and variations in intensity.

Background: Bird dog exercise (BDE) is one of the lumbar stabilization exercises that rehabilitate low back pain by co-contraction of the local and global muscles. Previous studies have reported the effect of various type of BDEs (for example, practicing the exercises on various surfaces and changing the limb movement) for muscle co-contraction. Objects: This study aimed to investigate the effect of knee joint flexion position of the raised lower limb on abdominal and back muscle activity during BDE in patients with chronic low back pain (CLBP). Methods: Thirteen males participated in this study (age: 32.54 ± 4.48 years, height: 177.38 ± 7.17 cm). Surface electromyographic (SEMG) data of the internal abdominal oblique (IO), external abdominal oblique (EO), lumbar multifidus (MF), and thoracic part of the iliocostalis lumborum (ICLT) were collected in two knee joint flexion positions (90° flexion versus 0° flexion) during BDE. The SEMG data were expressed as a percentage of root mean square mean values obtained in the maximal voluntary isometric contraction. Results: Greater muscle activity of the IO (p = 0.001), MF (p = 0.009), and ICLT (p = 0.021) of the raised lower limb side and the EO (p = 0.001) and MF (p = 0.009) of the contralateral side were demonstrated in the knee joint flexion position compared to the knee joint extension position. Greater local/global activity ratios of the abdominal muscle (i.e., IO and EO) of the raised lower limb (p = 0.002) and the back muscle (i.e., MF and ICLT) of the contralateral side (p = 0.028) were also noted in the knee joint flexion position. Conclusion: BDE with a knee joint flexion position might be recommended as an alternative lumbar stabilization exercise to enhance muscle activity in both the raised lower limb and the contralateral sides of the trunk for individuals with CLBP

Background: The scapulo-thoracic musculatures including serratus anterior (SA), upper trapezius and lower trapezius can provide shoulder stability and functional shoulder movement. Objects: The muscle activities of upper and lower SA were compared during three different scapular protraction exercises in healthy individuals in sitting position. Methods: Twenty-five healthy subjects were participated. Electromyography device was used to measure muscle activity of upper and lower SA and trapezius muscles. Each subject was asked to perform three different scapular protraction exercises (scapular protraction [SP], SP with self-resistance [SPSR], SPSR with hand-exerciser [SPSRH]) in random order. One-way repeated measures analysis of the variance and a Bonferroni post hoc test were used. Results: The muscle activity of lower SA muscle was significantly different among three conditions (SP vs. SPSR vs. SPSRH) (p < 0.01). The lower SA muscle activity was significantly greater during SPSRH compared to SP and SPSR, which required joint stability more than SP and SPSR (p < 0.01). Conclusion: SPSRH exercise can be recommended to facilitate the muscle activity of lower SA. In addition, the intramuscular variation in the upper and lower SA during scapular protraction exercise is required to consider the effective rehabilitation.

Background: Although the scapular posterior tilt movement could facilitate the lower trapezius (LT) muscle activity, no study identified the effects of the scapular posterior tilt movement on the selective activation of the LT muscle during prone shoulder extension. Objectives: To examine the influences of additional scapular posterior tilt on electromyography (EMG) of the upper trapezius (UT) and the LT muscles during prone shoulder extension. Design: Cross-sectional study. Methods: There were 15 asymptomatic male participants in this study who performed prone shoulder extension with and without scapular posterior tilt movements. For the scapular posterior tilt movements, participants performed visual biofeedback training for scapular movement using motion sensor. During the exercises, the EMG activity of the UT and LT was recorded using surface EMG system. Results: The EMG activity of the LT significantly increased during prone shoulder extension with scapular posterior tilt compared to that of general prone shoulder extension, whereas that of the UT was not significantly different between the two exercises. Moreover, scapular posterior tilt application significantly decreased UT/LT muscle activity ratio. Conclusion: Scapular posterior tilt movement may be emphasized during exercise when facilitating LT muscle activation.

Background: A hip fracture may occur spontaneously prior to the hip impact, due to the muscle pulling force exceeding the strength of the femur. Objects: We conducted falling experiments with humans to measure the activity of the hip muscles, and to examine how this was affected by the fall type. Methods: Eighteen individuals fell and landed sideways on a mat, by mimicking video-captured real-life older adults’ falls. Falling trials were acquired with three fall directions: forward, backward, or sideways, and with three knee positions at the time of hip impact, where the landing side knee was free of constraint, or contacted the mat or the contralateral knee. During falls, the activities of the iliopsoas (Ilio), gluteus medius (Gmed), gluteus maximus (Gmax) and adductor longus (ADDL) muscles were recorded. Outcome variables included the time to onset, activity at the time of hip impact, and timing of the peak activity with respect to the time of hip impact. Results: For Ilio, Gmed, Gmax, and ADDL, respectively, EMG onset averaged 292, 304, 350, and 248 ms after fall initiation. Timing of the peak activity averaged 106, 96, 84, and 180 ms prior to the hip impact, and activity at the time of hip impact averaged 72.3, 45.2, 64.3, and 63.4% of the peak activity. Furthermore, the outcome variables were associated with fall direction and/or knee position in all but the iliopsoas muscle. Conclusion: Our results provide insights on the hip muscle activation during a fall, which may help to understand the potential injury mechanism of the spontaneous hip fracture.

Background: Shoulder horizontal abduction in the prone position (SHAP) has been reported as an effective exercise to strengthen the lower trapezius. However, the effects of pre-emptive scapular posterior tilt on scapular muscle activity and scapulohumeral movements during SHAP have not been examined. Objectives: To examine the effect of the addition of scapular posterior tilt on muscle activity of the trapezius and posterior deltoid, and scapular posterior tilt and shoulder horizontal abduction, during SHAP. Design: Cross-sectional study. Methods: Fifteen healthy male subjects performed two types of SHAP: general and modified SHAP (SHAP combined with pre-emptive scapular posterior tilt). To perform modified SHAP, pre-emptive scapular posterior tilt training was performed prior to the modified SHAP. Muscle activity of the middle and lower trapezius and posterior deltoid, and the amount of scapular posterior tilt and shoulder horizontal abduction, were measured during two types of SHAP. Results: Muscle activity of the lower trapezius and scapular posterior tilt was significantly increased during the modified SHAP, while muscle activity of the posterior deltoid and the amount of shoulder horizontal abduction were significantly decreased. However, the middle trapezius muscle activity did not change during the modified SHAP. Conclusion: The SHAP with pre-emptive scapular posterior tilt can be useful to strengthen the lower trapezius.