Use of unstable training devices such as suspension systems for health and to enhance athletic performance are increasingly becoming popular (3–5). In particular, suspension systems are used and adapted by trainers to implement resistance training, providing users with numerous upper-body and lower-body exercise options (8,16). The TRX suspension system (TRX) is one such device that is used for purposes ranging from athletic conditioning to general fitness and rehabilitation (7,17).
Push-up exercises with TRX are performed by altering the degree of body angles from the prone position or by changing the height of the TRX straps from the ground level. In this type of exercise, the body weight is used against the gravity to perform multiplanar and multijoint resistance training (16,19). To accommodate resistance requirements of users, TRX straps are manipulated by modifying length, angles of push-pull, and body positions. With TRX, the loads encountered during the exercise are percentages of the user's body mass. This is important, as the degree of resistance experienced during resistance exercise is the basis of appropriate exercise prescription (14,17).
When resistance training exercises are performed with explicitly labeled masses like dumbbells, weight plates, and machines, training volume and intensity are calculated easily as a percentage of maximum loads (11). However, the quantification of intensity and load in suspension training systems such as TRX push-up is challenging.
There are many studies on push-ups, performed with different hand positions (9,10,12,13,23,24) on different platforms and surfaces (1,4,15) and also using suspension systems with muscle activation (2,8,16,17,19–21).
During standard push-ups, ground reaction forces reached up to 69% of body weight while the elbows were extended, and up to 75% of body weight while elbows were at flexion (10,12,13,18,22). When the hands were elevated on a 30.5-cm box, ground reaction forces dropped to 55% of body weight, and to 41% of body weight when the hands were elevated on a 61.0-cm box (11).
Melrose and Dawes (17) investigated loads during a 5-second static hanging position performed at 4 different body angles, extending elbows until subjects reached the supine position. This study revealed that as the angle increased from 30 to 75° between the subject and the ground, the subjects' arms encountered body mass resistance between 37.4 and 79.4%.
There is no likewise study to assess the load on upper and lower extremities during TRX push-ups at different angles. For this reason, it is vital to compare the impact on the upper and lower extremities during the TRX push-ups. The aim of this study was to assess the loads at different TRX angles as recorded by the ground force platform and the load cells attached to the straps. From these data, the percentage of body weight use was calculated, which provides guidance to prescribe training programs.
Experimental Approach to the Problem
This research was designed to determine the loads applied to the lower and upper extremities during TRX push-up exercises with various angles. The highest loads were recorded when elbows are in flexion and in extension. The effects on the load difference with the angle changes were evaluated. The dependent variables consisted of data recorded from the force platform, load cells (via straps). The independent variables were the 4 different vertical angles of the TRX push-ups.
Twenty-eight male physical education and sports university students (mean age = 24.1 ± 2.9 years, height = 179.4 ± 8.0 m, weight = 78.8 ± 9.8 kg) voluntarily participated in this study. Subjects had a minimum 1 year of resistance training experience, performing at least 2 sessions per week and a minimum of 3 months of suspension training experience, using this kind of training at least 1 time per week. They had no previous history of injuries of the upper and lower limbs in the last 6 months preceding the study. All subject were right handed. During the 0° TRX push-up application; 3 subjects with the upper extremity showing mostly fasciculation tremor, nonspecific pain complaint and/or insufficient stabilization, were excluded from the study. They gave their informed consent for the experimental procedure as required by the Declaration of Helsinki (1964) and Marmara University's ethics committee (Protocol: 0920140213, October 10, 2014).
Each subject took part in 2 sessions: familiarization and experimental, both at the same hour during the morning. The familiarization session was performed 48–72 hours before the data collection in the experimental session. Several restrictions were imposed on the volunteers: no food, drinks, or stimulants (e.g., caffeine) to be consumed 4 hours before the sessions and no arduous physical activities were allowed except daily routines 24 hours before the exercises. The same investigators made all measurements during the morning and the procedures were always conducted in the same laboratory (average temperature at 25° C).
Before testing, participants were familiarized with the push-up exercise on another TRX. Subjects practiced the exercises typically 5 times before tests. Height and body weight were measured with Tanita model BF- 350 (digital scales (0.1 kg) for body weight and fat).
The TRX suspension anchor (TRX angle) was set at right angle (90°) with the ceiling and this alignment was referred to as the zero (0°) angle reference point. The 4 different angles were measured with a goniometer using 2 laser pointer light streams originating at the main anchor, one vertical to the ground and the other aligned with the TRX straps.
The subjects performed dynamic warm-up exercises of the upper and lower limbs muscles for 10 minutes before the trials. The subjects were asked to grip the TRX handles set at strap mid length while standing on the force platform. Their feet were positioned shoulder width apart. The subjects adopted a traditional push-up starting position with elbows at extension. They maintained this isometric contraction for 4 seconds while maintaining a neutral spine position. Then the subjects began the flexion phase of the push-up until the correct depth was reached (chest reaching the level of the hands). Finally, the elbows were extended to full length (starting position). This push-up exercise was repeated 5 times and the elbows were kept at extension for 4 seconds after the fifth run. This movement scheme was repeated for all TRX angles, respectively (45, 30, 15, and 0°). Subjects rested 2 minutes between each test. A metronome (Quartz Metronome; Seiko Instruments Inc., Hong Kong, China) was used to control the cadence of the push-up repetitions. Each flexion and extension phase was performed in 1 second (1 second up and 1 second down). Verbal feedback was given to the subjects by an experienced trainer to maintain the range of movement, correct body position, and hand distance during the data collection. A trial was discarded and repeated if participants were unable to perform the exercise with the correct technique.
A TRX Suspension device (TRX Suspension Trainer; Fitness Anywhere, LLC, San Francisco, CA, USA) was used for the suspension push-up exercises. The TRX Suspension Trainer, was anchored to the ceiling according to the manufacture's manual (6). The height for the TRX handles was set at 60 cm (strap mid length) from the ground level.
To record the load on the TRX straps, load cells (Cas Coop, Seol, Korea) were fitted between the cam-buckles on both sides (Figure 1). Data were collected (sampling rate 100 Hz) by the specific indicator (PC30A Data Logger; Kyowa Inc., Korea) and its original software (PCD 30; Kyowa Inc.).
The test was conducted with the subjects' feet placed on the force platform (sampling rate 100 Hz, MatScan System) while gripping the TRX handles (MatScan System; Tekscan, Inc., Boston, MA, USA). The data were recorded by original software for MatScan System. Calibration of the system was performed according to the manufacturer's recommendations in the manual.
TRX push-up trials were conducted at 4 angles (45, 30, 15 and 0°; Figure 2). Body positions and movements were visually monitored and recorded by a 30 fps camera (TRV900E; Sony).
The recorded load data from the load cells integrated in the TRX device were analyzed separately for the extension and flexion phases. Subjects were instructed to do 5 push-ups at each angle. Maximum force values reached in flexion and extension phases during the TRX push-up were used in this study.
The first and fifth repetitions were excluded from data analyses. Only the mean of the second, third, and fourth values were used. The values obtained from the load cells in the TRX straps were classified as loads borne by the TRX straps and those obtained from the force platform as loads borne by the force platform.
The recorded loads were normalized by body weight (loadnorm = load/body weight × 100). Using this normalized loads, the distribution on the straps and on the force platform was expressed as percentages of the total load.
One-way analyses of variance with Scheffé and Dunnett C post hoc procedures were used to compare the difference between measurements of each angle (45, 30, 15, and 0°). Levene homogeneity of variance test performed to decide the equality of variances. According to homogeneity test results, Tukey and Dunnett C post hoc tests were performed. The significance level was set at 0.05.
Force values differences, normalized to subjects' body weights and angles are shown in Table 1. When loads at the varying TRX angles were compared, the differences between the loads were significant both for the flexion and extension phases, and this was valid for the TRX straps as well as for the force platform values (p = 0.000). Post hoc comparisons revealed that between all angles there were significant differences (p ≤ 0.05). The difference between the dominant and nondominant arms was not significant (p > 0.05).
With decreasing angle, the loading on the TRX steadily increased while the loads on the force platform steadily decreased. On the TRX straps, the transition from 45 to 0° resulted in more than a twofold increase of loading for the flexion and in more than a fourfold increase for the extension phase. In comparison, the decrease of loading on the force platform was comparable for the flexion but less pronounced for the extension phase. The transition from 45 to 0° decreased ground reaction forces to less than half for both phases (Table 2).
When the elbow is in flexion, with the increase in the TRX angle, the load on the TRX straps decreases as the load on the force platform increases (Figure 3). And the measurements with the elbow extension, at 0° the load on the TRX straps and the force platform are similar. As the angle increases, the load on the TRX dramatically decreases and the load on the force platform dramatically increases (Figure 4).
As can be seen from Table 3, the distribution of the load on the dominant and nondominant arms was alike. This similarity could also be observed on the force platform.
In this study, it has been determined that with the increase of the angle during the TRX push-up exercise, the load on the straps decreases. When the TRX angle is set at 0° and the elbows were at extension, 50.4% of the body weight was recorded from the TRX straps, and when the elbows were at flexion, 75.3% of the body weight was on straps. This study also shows that with varying angles, the load on the TRX straps are similar for both left and right. Therefore, the subject's dominant and nondominant arms pose no difference in the workload, which means the exercise is symmetrical.
During the standard push-up exercise (SPU), the loading with the elbows in flexion was reported to be 75% of the bodyweight, whereas in extension it was 64–69% of the body weight (11,18,22).
In the above-mentioned studies, the values calculated when the elbows at flexion were similar to the ones that were calculated with TRX angle at 0° in this study (the closest position the SPU). During the elbows extension at SPU (11,13,18,22), the values calculated were 27–37% higher compared with this study. The TRX handles being 60 cm higher from the ground and the elbows in extension causes the upper body to be higher from the ground than in the position during the SPU. This position causes the load to be transferred to the lower extremities.
The hand-elevated exercise that Ebben et al. (11) used with the 61-cm box is similar to the exercise used in this study. Ebben et al. (11) showed that for this position where the elbows were in extension, the subject worked with 41% of the body weight. In this study for the same height, the load was found to be 23% higher than the load mentioned in the study of Ebben et al (11). This could be due to the unstable surface of TRX push-up and the difference in the cadence in the study of Ebben et al. (12) (2 seconds up and 2 seconds down). This is also compatible with the argument of Mier et al. (18), which is, “the difference in cadence changes the relative load”. Another source for the difference might be that Ebben et al. (11) collected the data on the average of only 2 push-ups. Gender differences might also be the cause of the dissimilarities in the study of Ebben et al. (11).
Melrose and Dawes (17) used the angle between the subject and the floor instead of TRX's anchor connection point as in our study. The above-mentioned study, even with the differences in the design, has the closest set-up to our study. In the study from Melrose and Dawes (17), the increase in the load on the TRX straps as the angle of the subject decreases from the floor is similar to our study. However, because of the method of angle measurement difference from our study, there has not been a comparison for all the angles.
The loads on the TRX straps increased both in the extension and flexion phases as the TRX angle decreased. The highest load was recorded when the angle was at 0° in flexion phase and the lowest was recorded when the angle was at 45° in extension phase. Both in the flexion and extension phase, decreases in TRX angle result in a linear reduction of the load on the force platform (Figures 3 and 4). As the subject reaches the erect position with the TRX at 45°, most of the body weight is recorded in the force platform. When the TRX angle was set at 0° and elbows extended, the load on the TRX straps and that exerted by the feet on the force platform were nearly equal. However; when the elbows were in flexion and at TRX angle 0°, the load on the straps increased and the load on the force platform decreased. It is stated in the TRX manual that TRX push-ups are harder to perform when the angle is at 0° (6). This can be explained by the challenge in maintaining the body balance and stabilization at 0° in TRX push-up position, and also because of the exposure to the higher loads by the upper-body limbs. The stabilization difficulty of the subject at 0° extension could be due to the bodies and extremities angles (becoming more parallel to the floor) and to the threefold (317%) increase in load at this position (Table 2). This study revealed that the challenge of TRX push-ups mainly originated from the flexion phase at narrow angles between 0 and 15° as the load increased on the upper limbs. For this reason, resistance training of the upper extremities using TRX should be conducted at 0 and 15° angles, especially in the flexion phase.
There are several limitations to the results of this study. Subjects were of single gender, and the loading was not measured at the center of the subject's body.
In future studies, data should be collected from the static halts for the elbows up (extension) and down (flexion) position. Information from the hands on the local distribution of force could also be gathered, using gloves with force sensors. Different heights and angles of the TRX straps can also be evaluated.
The loads on the TRX straps increase by decreasing the TRX push-up application angle (45–0°). Throughout all angles, the applied load is higher during the flexion phase than the extension. During the TRX push-up exercise, the lowest load applied to the arms and the straps of the TRX is at the 45° extension position. For beginners with TRX push-up exercises, it would be advisable to start with isometric exercises at elbows extended position at 45 and 30° instead of TRX push-ups including flexion and extension at 45°. TRX push-ups including flexion and extension at 45–30° can be applied gradually after this phase. There was more than fourfold increase in the loading on the upper extremities when the TRX angle was changed from 45 to 0°. Rapid transition from the angle of low-intensity training at 45–0° without any gradual transition at 30–15°, will result in increased load on the fourfold upper limbs. It is recommended to plan the trainings with a gradual increase to prevent any injuries. Following this, the TRX angle can be reduced to facilitate progression of training intensity. The TRX angle at 0° provides the most challenging upper extremities push-up exercise, particularly as the arms move from extension to flexion.
I thank the employees of Marmara University Medical Faculty Prosthetic and Orthotic Laboratory and Marmara University Center of Sports Sciences and Athletic Health, Dr. Yasar Tatar, Dr. Nusret Ramazanoglu, Dr. Semih Yilmaz for their contributions.
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