Muscle Activity During Bridge Exercises on Different Types of Floor Surfaces

Home , Bridge (exercise)

J Phys Fitness Sports Med, 10 (4): 199-203 (2021) DOI: 10.7600/jpfsm.10.199 JPFSM: Regular Article Muscle activity during bridge exercises on different types of floor surfaces

Jumpei Takahashi1*, Hiroto Suzuki2, Naoki Tanaka3 and Toru Nishiyama4

1 Hirosaki University Graduate School of Health Science, 66-1 Hon-cho, Hirosaki-shi, Aomori 036-8564, Japan 2 Department of Rehabilitation, Faculty of Medical Science and Welfare, Tohoku Bunka Gakuen University, 6-45-1 Kunimi, Aoba-ku, Sendai-shi, Miyagi 981-8550, Japan 3 Faculty of Health Care and Medical Sport, Teikyo Heisei University, 4-1 Uruido-minami, Ichihara-shi, Chiba 290-0193, Japan 4 Department of Rehabilitation, Japan Health Care Collage, 6-17-3 Megumino-nishi, Eniwa-shi, Hokkaido 061-1373, Japan

Received: October 27, 2020 / Accepted: November 26, 2020

Abstract Bridge exercises help strengthen the muscles of the lower limbs and trunk. Previ- ous studies have examined muscle activity during bridge exercises using balance balls and balance mats during which the body’s balance is only partially disturbed. However, no study has examined muscle activity during bridge exercises when performed on an air mattress, during which the entire body is not balanced. Therefore, the purpose of this study was to verify the differences in muscle activity during bridge exercises when performed on a hard surface like a platform or on an air mattress. Twenty-four healthy university students were instructed to perform bridge exercises using three different knee joint angles (90°, 110°, 130°) and two different types of floor surfaces. Muscle activity of the erector spinae, gluteus maximus and lateral hamstrings was measured by using a surface electromyograph, Each muscle showed significantly higher levels of muscle activity during certain knee joint angle conditions when performed on an air mat (p < 0.05). In the erector spinae, muscle activity at 90° was significantly higher than at 130° of the knee joint in the air mattress condition. For the gluteus maximus, there were no significant differences among the angles of the knee joint. The results of this study show that muscle activity while performing bridge exercises increases when the entire body is placed on a soft surface. Keywords : muscle activity, bridge exercise, exercise surface

position. A method based on varying difficulty of bridge Introduction exercises improves the muscle activity of agonists. During Bridge exercises help strengthen the back muscles. In acute rehabilitation, bridge exercises are sometimes per- rehabilitation, bridge exercises are used to strengthen formed in hospital rooms on soft air mattresses originally hip extensors and back muscles in the supine position1-7). designed to prevent bedsores. The bridge exercise on the Back training exercises like bridge exercises are useful bed is an easy way to perform back-side strength training for healthy individuals and in various disorders such as while lying down. Strengthening the gluteus maximus, lower back pain, trochanteric pain syndrome and cerebral erector spinae and hamstrings can lead to anti-gravity palsy8-14). activities such as walking and standing up movements. It The erector spinae, gluteus maximus and hamstring has been reported that the use of air mattresses is highly muscles are the main muscles involved in bridge exer- effective in preventing bedsores, but it is difficult to move cises. But muscle activity has also been found in the rec- and the muscle activity during movement is different from tus abdominis muscle, the external and internal oblique that of standard mats19). Although muscle training on an muscles, as well as in the gluteus medius muscle and the entirely unstable support base is a necessary exercise to quadriceps femoris2,5-7,15). improve muscle strength for daily activities after recovery Various bridge exercises, like those using variations in from bed rest, it is unknown how it affects muscle activity knee and hip joint angle16), using balance balls and balance during bridge exercises. Moreover, if we can reveal the mattresses2-6,15,17), as well as the one-leg bridge6-8,11,14,17,18) muscle activities of the bridge movement, which is dif- have been studied. The findings suggest that, in most ficult to perform with not only the feet but also the upper cases, muscle activity was greater when bridge exercises body in an unstable state, we can propose this method as a were performed in an unstable position than in a stable strength training method to efficiently increase the muscle activity at the same time. *Correspondence: [email protected] The purpose of our study was to evaluate the difference 200 JPFSM: Takahashi J, et al. between muscle activity during bridge exercises when data taken from the middle 3 seconds. performed on a hard surface, like a platform, or on an air After MVC data were measured, the participants were mattress. Particular focus was given to the hardness of the given time to rest, and measurements during bridge ex- entire floor surface during the exercises. ercises were carried out. The electromyography data was imported into a computer using a 16-bit analog-to-digital converter, with a sampling frequency of 1 kHz. Each test Materials and Methods was performed three times under each condition, and the Participants. Subjects were 30 university students who test order randomized. To avoid the effects of fatigue, consented to the study, and analysis was performed on 24 there was a one-minute pause between each test. of the subjects who had no deficient data. The inclusion EMG data were analyzed using data collected during criteria were no orthopedic or neurological disorders. For the middle 3 seconds of the exercises performed under ethical considerations, purpose, content and potential dan- each condition. The resulting EMG waveforms were sub- gers of our study were explained to the participants ver- jected to a 10-Hz high-pass filter, and the integrated value bally and in written form and consent to participate was was calculated after full-wave rectification. As an index obtained in writing. Measurements were carried out after of the amount of muscle activity, normalized values of the approval by Tohoku Bunka Gakuen University’s Ethics integrated values under each exercise condition were used Committee (approval number: BUNDAI No.14-17). (the integrated value during maximum voluntary contrac- tions was considered as 100%), and the average of values Experimental design. Bridge exercises were performed obtained from 3 measurements under each condition cal- under 3 different conditions pertaining to the knee flex- culated. ion angle (90°, 110° and 130°). The initial limb position was as follows: the knee joint was placed in the angles Statistical analysis. For statistical analysis, a two-way instructed in each experimental condition, the arms were ANOVA for both factors (bed type and knee flexion folded in front of the chest, and the entire sole surfaces angle) were performed. As a post-hoc test, a paired t-test of both feet were placed in contact with the bed surface. was performed for the comparison of muscle activity by The participants were instructed to carry out bridge exer- bed type. One-way analysis of variance was performed cises while elevating the buttocks to a height where the for the comparison of different knee flexion angles, and hip joint angle was 0° and the posture was maintained for Bonferroni correction was carried out as a post-hoc-test. 5 seconds. The participants were instructed to keep their A p-value < 0.05 was considered as significant. feet sole surfaces on the bed surface while maintaining this posture. Results The bridge exercises were performed on 2 types of surfaces. A platform was used for the conditions using a hard In the erector spinae muscles, the main effects of bed surface, and an air mat ADVAN (molten Co.) was used type were absent, and there were no interactions; only the for the conditions using a soft surface. In both conditions, main effects of the knee joint angle were found. The re- the participant’s entire body was positioned in such a way sults of post-hoc tests suggested that muscle activity was that it rested firmly on the platform or air mattress. significantly higher when using an air mat than a platform The muscle activity data collected during the exercises during the 90° knee joint angle condition (p < 0.05) (95% were used for measurement. By using a surface electro- confidence interval [CI] -5.90 to -0.67). Comparison by myography (EMG), the data was derived using a bipolar knee angle showed significantly higher muscle activity at lead. The following 3 muscles were examined: erector 90° than at 130° for the air mat condition (Table 1). spinae, gluteus maximus and lateral hamstrings. Elec- In the gluteus maximus muscle, the main effects of bed trodes were attached as follows, referring to the method type were found with interactions. But there was no main of Delagi et al.20): to erector spinae muscles 3 cm lateral effect concerning the knee joint angle. The results of post- to the spinous process, to gluteus maximus muscle half hoc-tests showed that under conditions using knee joint way between the trochanter and the sacral vertebrae, angles of 130° and 90°, the muscle activity was signifi- and to lateral hamstring muscles at the midpoint of the cantly greater under exercise conditions using an air mat- line connecting the peroneal head and sciatic tuberosity. tress (p < 0.05) (95% CI -4.13 to -1.39, -4.21 to -1.41). Before measurements, the skin was exfoliated using medi- However, there was no significant difference in the com- cal sandpaper to minimize electrical resistance, and the parison of knee joint angles (Table 2). electrodes were attached on the right side. EMG data was In the lateral hamstrings, only the main effects of the then collected during maximum voluntary contraction knee joint angle were found. The main effects of bed type (MVC) by using the examiner’s manual resistance. MVC were absent, and there were no interactions. Concerning measurements were performed in a prone position follow- the results of post-tests, muscle activity was significantly ing the manual muscle testing method of Daniel et al.21), higher during the 130° condition when the air mat was with maximum strength being exerted for 5 seconds, and used (p < 0.05) (95% CI -5.89 to -0.67), but the difference JPFSM: Muscle activity during bridge exercises on different types of floor surfaces 201

Table 1. IEMG of erector spinae m. (%)

ROM of knee flexion 130° 110° 90° Floor surface

Platform*1 30.8±11.7 34.6±12.2 37.9±11.7

Air mattress*1 31.8±12.2 34.6±11.1 41.1±12.7 IEMG; integrated electromyography (Average ± SD) *; p < 0.05

Table 2. IEMG of gluteus maximus m. (%)

ROM of knee flexion 130° 110° 90° Floor surface

Platform 10.1±5.4 11.0±5.9 9.6±4.8

Air mattress 12.9±6.9 11.9±6.7 12.4±5.6 *; p < 0.05 (Average ± SD)

Table 3. IEMG of lateral hamstrings m. (%)

ROM of knee flexion 130° 110° 90° Floor surface

Platform*1 10.5±8.2 2323.0±120±12.4 40.7±17.7

Air mattress*1 11.8±7.9 23.0±13.0 41.3±16.7 *; p < 0.05 (Average ± SD)

was small. Significant differences were found among than on platforms. A previous study suggested that when joint angles, and that smaller joint angles were associated bridge exercises were performed using air cushions under with significantly greater muscle activity (Table 3). the soles, the muscle activity of the erector spinae muscles, biceps femoris muscle and gastrocnemius muscle increased significantly compared to conditions with no air Discussion cushion, whereas muscle activity of the rectus abdominis, The exercises on air mattresses were performed on a rectus femoris and tibialis anterior remained unchanged5). bed whose entire surface was soft. Though there was A similar study using air cushions suggested that the good prevention against pressure ulcers, it was difficult muscle activity of the external oblique muscle, erector to perform exercises with movements such as rolling spinae muscles and biceps femoris muscle increases6). over. Our findings suggest that muscle activity is higher In contrast, concerning bridge exercises performed us- in bridge exercises when performed on air mattresses ing a balance pad and an air cushion or a balance ball 202 JPFSM: Takahashi J, et al. inserted under the soles, the muscle activity of the erector always observed. For the present subjects, it seems that spinae muscles, abdominal muscles, and gluteus maxi- bridge movement in each condition was not enough for mus muscle remained unchanged15). The results of these the changes to be clearly seen. On the other hand, there previous studies showed that the muscle activity of the was a significant difference in the gluteus maximus and erector spinae was not consistent, and the muscle activ- lateral hamstrings at 130°. This may be because the center ity of the gluteus maximus was not affected by unstable of gravity moved upwards while bridge exercises were conditions. However, in the present study, the activity of performed as mats with unstable parts at the trunk level the erector spinae, gluteus maximus and hamstrings was may have sunk (compressed). Yoshida et al.23) reported affected. Unlike previous reports, our findings suggest that when there were two contact points on the floor at that the entire base of support being unstable may have an different heights, the load was applied to the lower con- impact. In the previous studies, exercises were performed tact point. In other words, if the subjects perform a 130° under conditions in which only the soles were unstable. knee flexion bridge on the air mat, more load is added to Depending on the severity of the instability, the impact on the trunk side of the body than at other knee angles, and muscle activity may, therefore, be smaller in some cases. it is expected that the trunk will be pressed against the air However, poor stability affected both the lower limbs and mat and the upper body will be stable. In contrast, since the trunk’s base of support in our study. This can possibly the instability of the foot surface was maintained, it was explain why muscle activity increased more markedly. estimated that the muscle activity of the lateral hamstrings In addition, we thought that more detailed results could at 130°, which is usually considered to be less active, was be obtained by setting up the knee joint angle condition. increased. However, because we did not quantitatively In the erector spinae, there was a significant difference measure the degree of subduction of the trunk, the effect between two floor surface conditions at 90°, and between cannot be clearly examined. 90° and 130° in the platform condition. There was no an- Interestingly, there was no significant increase in any gle effect in the air mattress condition. In both conditions, muscle activity between floor surface conditions at 110° there was a similar trend of increased muscle activity as of knee joint. The position of 110° in this study is defined the angle became smaller, which is similar to data reported as the general flexion angle during bridge movement, and by Lee et al.22). The gluteus maximus muscle did not dif- the movement itself is standard. In other words, since the fer significantly among the knee joint angle conditions, burden on the foot side and the trunk side was not unbal- but there was a significant difference between the floor anced during bridge exercise, the deviation in the center conditions at 90° and 130°, indicating that the influence of gravity did not occur and the efficiency of the muscle of floor surface conditions is more likely to be affected activity may have been good. This issue also needs fur- by small or large knee joint angles. The lateral hamstrings ther investigation in the future. showed a significant difference between the floor condi- This study showed that when bridge exercise was car- tions at a 130° knee joint angle; and furthermore, both ried out on a soft airbed, the exercise load was likely to conditions showed an increase in muscle activity at small- be greater than during exercise workouts conducted on er knee joint angles. The reason why the muscle activities conventional beds. Therefore, we consider that it is a of the erector spinae and lateral hamstring muscles were simple and easy-to-use method for increasing the load of greatest at 90° is because the distance between the trunk strength training that can be adopted immediately. Future and the sole surface increased when the knee joint angle studies should evaluate comparisons of bridge exercises was small during bridge movement. This can possibly ex- performed under conditions in which only the feet are un- plain why muscle activity increased more markedly in the stable, as well as evaluate the features of muscle activity erector spinae muscles (which needs the trunk to be more during exercises performed on a soft bed. stable) as well as in the lateral hamstrings muscle (which needs the lower extremity to be more stable). Similarly, Conflict of Interests a previous report suggests that in bridge exercises performed on a stable bed, an increase in the knee flexion The authors declare that there is no conflict of interests regard- angle was accompanied by an increase in muscle activity ing this article. in the gluteus maximus muscle, and that a decrease in the knee flexion angle is accompanied by increased muscle Author Contributions activity in the hamstring muscles16). In this study, the lateral hamstrings showed similar results, but the gluteus The study was designed by JT, HS and NT. The experiments maximus muscle did not vary with the knee angle. One of were conducted by JT, HS and NT. JT, HS and TN analyzed the the reasons why the activity of gluteus maximus muscle data, and JT and HS wrote the manuscript. All authors approved did not change with knee joint angle is that %MVC val- the final version of the manuscript. ues were too low (about 10%) to reveal the change in muscle activity. Since bridge exercise involves hip exten- sion, the contraction of the gluteus maximus muscle is JPFSM: Muscle activity during bridge exercises on different types of floor surfaces 203

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