Introduction
The use of ropes as a training element to improving physical conditioning has been studied for more than 30 years (13,25). For example, jump ropes are considered a cardiovascular exercise that allows a stretch-shortening cycle movement (17) and demonstrated to being a good conditioning method to improve cardiovascular function (13), coordination (19), and even have some benefits in shoulder strength (8). A new way of training with ropes is the use of large diameter and heavier ropes called battle ropes. Battle rope training, consisting in undulating a rope with the upper body, has increased its popularity as a physically demanding activity (10). Fountaine and Schmidt (10) showed that 10 sets of 1-minute bouts of battle rope with 45-second rest between sets resulted in elevated heart rates and energy expenditure, providing a vigorous cardiovascular workout. In the same vein, Ratamess et al. (20) recently found that 3 sets of 30-second bouts of battle rope exercise with 2-minute rest intervals between sets resulted in the largest energy expenditure among 13 different traditional resistance exercises performed at moderate-heavy intensity.
As mentioned above, battle rope exercises are normally performed at maximal speed during a given time, allowing a high number of repetitions and resulting in a vigorous cardiovascular workout (10,20). Besides this, the use of battle ropes during a high number of repetitions must also provide a great stress for several muscles, especially for those core muscles that are a base to resist or generate torques. However, the aforementioned literature was conducted to evaluate the metabolic cost, no studies have measured muscle activity during battle rope exercises. Core strengthening has been a hot topic during the last decade because of their important implications in rehabilitation, injury prevention, and sport performance (3,27), especially in those sports performed under unstable environments (3) or involving throwing-type motions (27).
Battle ropes are anchored at a fixed point allowing for different types of waves and movements. For instance, Fountaine and Schmidt (10) used bilateral arm waves in their battle rope protocol, whereas Ratamess et al. (20) used 3 different battle rope variations in the same exercise (unilateral alternating waves, bilateral waves with a half-squat, and bilateral rope slams with a half-squat). Different loading implications and asymmetrical movement patterns have been found during unilateral and bilateral training exercises (15), and muscle activity patterns and levels—as measured with electromyography (EMG)—are therefore likely to vary (6). Unilateral compared with bilateral actions can, in some movements, produce greater core activity because of the contralateral muscle stimulation (23). For instance, unilateral dumbbell shoulder press provoked greater external oblique (22) and higher erector spinae muscle activity than the bilateral counterpart either with absolute (4) or relative loads (22). Greater transverses abdominis and internal oblique activity were also found during the unilateral chest press when compared with bilateral press both performed with absolute loads (4). Similarly, Santana et al. (23) found greater erector spinae, rectus abdominis, internal, and external oblique when performing standing unilateral cable press compared with the typical bilateral bench press.
Proper exercise selection and intensity are crucial factors to induce the desired adaptations (20). As differences were noted in the literature analyzing unilateral vs. bilateral movements especially affecting core musculature and there is no knowledge about the effect of using battle ropes in muscle activity, EMG assessment is needed to measure muscle activity patterns, levels (intensity), and effectiveness (6) during these exercises. Hence, the aim of this study was to analyze muscle activity of various core and upper limb muscles during unilateral alternating waves vs. bilateral waves of battle rope exercise. We hypothesized that unilateral alternating waves would provide higher core muscle activity as compared with bilateral waves.
Methods
Experimental Approach to the Problem
To examine the hypothesis of this study, 21 volunteers participated in a repeated-measures study on 2 different occasions. Normalized EMG was the dependent variable, and the 2 different types of waves were the independent variables. During the first session, subjects were familiarized with the movements and protocol, whereas in the second session, they performed 3 repetitions of each movement with EMG data collection: bilateral waves and unilateral waves (Figure 1) in a randomized order. This assessment allowed us to evaluate the muscle activation differences during the 2 exercises performed. Surface EMG signals were recorded from the anterior deltoid (AD), external oblique (OBLIQ), lumbar erector spinae (LUMB), and gluteus medius (GM). Data obtained from each individual muscle during each dynamic exercise were normalized to the maximal muscle activity obtained during maximum voluntary isometric contractions (MVIC). Specifically, the study design attempted to answer the following research question: “Are there differences in the muscle activity extent during the performance of different wave movements?”
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Figure 1: Different battle rope exercises: (A) Bilateral waves, (B) Unilateral waves.
Subjects
Young fit male university students (n = 21; age: 23 ± 2.15 years; height: 177.63 ± 7.17 cm; body mass: 79.12 ± 9.1 kg; body fat percentage: 11.82 ± 2.29%) participated in the study on a voluntary basis. Subjects had a minimum of 1 year of resistance training experience, performing at least 2 sessions per week at moderate to vigorous intensity. All subjects were free from musculoskeletal pain, neuromuscular disorders, or any form of joint or bone disease. This study was performed during the spring of 2014. All subjects signed an institutional informed consent form before starting the protocol, and the institutions' review board approved the study. All procedures described in this section comply with the requirements listed in the 1975 Declaration of Helsinki and its amendment in 2008.
Procedures
Each subject took part in 2 sessions: familiarization and experimental sessions, both at the same hour during the morning. The first session occurred 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 3–4 hours before the sessions and no physical activity more intense than daily activities 12 hours before the exercises. They were instructed to sleep at least 8 hours the night before data collection.
During the familiarization session, height (IP0955; Invicta Plastics Limited, Leicester, England), body mass, and body fat percentages (Tanita model BF-350) were obtained. Then, subjects were familiarized with the battle rope exercises (using battle ropes with a 15 m length, 4 cm diameter, and 14 kg weight), movement amplitude, body position, and cadence of movement that would later be used during data collection. Subjects practiced the exercises until they felt confident and the researcher was satisfied that proper form was achieved.
The protocol started with a light warm-up where each subject performed 5 minutes of mobility drills without ballistic movements and performed 1 set of 10 battle rope repetitions (5 repetitions of bilateral and 5 repetitions of unilateral movements). Then, the protocol continued with the preparation of subjects' skin and followed by electrode placement, checking the EMG signal, MVIC collection, and exercise performance. Hair was removed from the skin overlying the muscles of interest, and the skin was then cleaned by rubbing with cotton wool dipped in alcohol for the subsequent electrode placement, positioned according to the recommendations of Cram et al. (7), on the AD, OBLIQ, LUMB, and GM on the dominant side of the body. Pregelled bipolar silver/silver chloride surface electrodes (Blue Sensor M-00-S; Medicotest, Olstykke, Denmark) were placed with an interelectrode distance of 25 mm. The reference electrode was placed between the active electrodes, approximately 10 cm away from each muscle, according to the manufacturer's specifications. All signals were acquired at a sampling frequency of 1 kHz, amplified and converted from analog to digital. All records of myoelectrical activity (in microvolts) were stored on a hard drive for later analysis. To acquire the surface EMG signals produced during exercise, an ME6000P8 (Mega Electronics, Ltd., Kuopio, Finland) biosignal conditioner was used. Before the exercise performance described below, two 5-second MVICs were performed for each muscle and the trial with the highest EMG selected. Participants performed 1 practice trial to ensure that they understood the task. One minute of rest was given between each MVIC, and verbal encouragement was provided to motivate all participants to achieve maximal muscle activity. Participants initiated the MVICs after they hear “ready, steady, go” and then verbal encouragement consisted of the researcher speaking in a loud voice, “harder, harder, harder.” Positions during the MVICs were based on standardized muscle testing procedures for the (a) AD (9), (b) OBLIQ (26), (c) LUMB (14), and (d) GM (14) and were performed against a fixed immovable resistance (i.e., Smith machine). Specifically, (a) deltoid flexion at 90° in a seated position with erect posture and no back support, (b) curl up at 40° with arms on the chest and pressing against the bar in an oblique direction with the participant lying on the bench, with the feet flat on the bench, and the knees bent at 90°, (c) trunk extension with the participant lying on the bench and pelvis fixated, the trunk was extended against the bar, and (d) hip abduction at 30° against the bar with the participant positioned side lying on their nondominant limb.
In accordance with a previous protocol (10), subjects started the battle rope with feet shoulder width apart, with the trunk flexed forward to approximately 30–45° and using a half-squat position. Subjects held the ends of the rope with a neutral grip, with the arms straight and relaxed at their side. During the exercise performance, subjects were asked to use minimal lower body and trunk movement as to generate the waves primarily through shoulder flexion when raising the ropes and shoulder extension when crashing the ropes to the floor. Each subject performed 3 consecutive repetitions in the 2 conditions, bilateral waves and unilateral waves, with 2 minutes of resting between exercises. A metronome set at 70 bpm was used to regulate the cadence of each wave movement. Visual feedback was given to the subjects to maintain the range of movement and hand distance during the data collection (Figure 1).
Statistical Analyses
During later analysis, all raw EMG signals obtained during MVICs and during the exercises were digitally filtered, consisting of high-pass filtering at 10 Hz and a moving root-mean-square (RMS) filter of 500 milliseconds. For each individual muscle, peak RMS EMG of the 3 repetitions performed at each level was determined, and the average value of these 3 repetitions was then normalized to the maximal RMS EMG obtained during MVC (12,24).
A 2-way repeated-measures analysis of variance (Proc Mixed, SAS version 9; SAS Institute, Cary, NC, USA) was used to determine if differences existed between exercises and muscles. Factors included in the model were exercise (unilateral and bilateral rope swing), muscle (4 muscles), and exercise by muscle interaction. Normalized EMG was the dependent variable. Values are reported as least square means (SE) unless otherwise stated. p values <0.05 were considered statistically significant.
Results
Table 1 shows normalized EMG during the unilateral and bilateral battle rope waves. For AD, there was no significant difference between conditions (p = 0.227). OBLIQ activation was significantly greater (p = 0.02) with the unilateral waves compared with the bilateral waves. Gluteus medius activity showed no significant difference between conditions, although a tendency was observed (p = 0.054). Lumbar erector spinae signal was significantly higher (p = 0.001) with the bilateral waves compared with the unilateral waves.
Table 1: Normalized muscle activity during bilateral and unilateral waves (n = 21).*†
Discussion
This is the first study to quantify muscle activity during battle rope exercise. Partially in agreement with our hypothesis, unilateral alternating waves generally provided higher core muscle activity as compared with bilateral waves. Our main finding is that unilateral alternating waves produced greater OBLIQ muscle activity than the bilateral waves, whereas the contrary result was found for the LUMB.
Despite the lack of EMG studies investigating battle rope movements, the use of unilateral vs. bilateral actions during other strengthening exercises has been more described. In line with our results, greater OBLIQ activation during a unilateral dumbbell shoulder press was reported by Behm et al. (4) and Saeterbakken and Fimland (22) in comparison with the bilateral action. Similarly, Santana et al. (23) found greater external oblique when performing a standing unilateral cable press with a pulley compared with the bench press. It was stated that unilateral-resisted movements may enhance disruptive torques to the body, producing higher instability conditions (3). In fact, different load and movement patterns were found during a biomechanical comparison of unilateral/bilateral power snatch liftings (15). Because the external oblique acts as a rotator and trunk stabilizer (1), higher muscle activity of the external oblique will be expected when greater disruptive torques are produced during unilateral waves to stabilize the core allowing greater postural control. In addition, the counterbalance that is allowed by bilateral waves decreases the disruptive torques during the exercise and thus the EMG values (22). Literature findings clearly show that unilateral rather than bilateral movements (4,22,23) and standing rather than seated positions (22) are the best options to enhance OBLIQ muscle activity.
Regarding the LUMB muscle results, our findings were not expected because we found that bilateral waves induced higher activation than unilateral waves. In contrary, Santana et al. (23) found greater LUMB activity during a standing unilateral chest press with a pulley compared with the chest press. Similarly, other authors reported higher LUMB muscle activity either with absolute (4) or relative loads (22) when the shoulder dumbbell press was performed unilaterally compared with bilaterally during seated (4) and bipedal position (22). The key difference may be that the body needs stabilization primarily in the sagittal plane during battle rope movements, whereas stabilization is required more so in the frontal and transverse plane during unilateral pressing movements. Moreover, although the previous studies used a relative load for each condition, we used the same absolute load that provides the rope. Furthermore, in the investigation conducted by Saeterbakken and Fimland (22), the authors did not find LUMB muscle activity differences during unilateral and bilateral dumbbell presses performed with relative loads in a seated position. In this study, we used a semisquat position that was maintained during the performance of the waves, and maybe the stability disruptions during this position and exercise are not the key factors to enhance LUMB muscle activity. In fact, Saeterbakken and Fimland (22) only found greater LUMB activity when participants progressed to the exercise variation with the highest stability requirements (i.e., standing position). In accordance with our results, a similar body position while subjects performed a bilateral upper extremity flexion reported higher longissimus thoracis activation compared with unilateral shoulder flexions with absolute load (1). Similarly, Behm et al. (4) did not find EMG differences in upper erector spinae during the bilateral and unilateral shoulder exercise. Literature findings suggest that unilateral movements especially affect the abdominal wall musculature, as other muscles such as transversus abdominis and internal oblique (4) or the rectus abdominis and the internal oblique (23) also showed higher activity during these movements compared with their bilateral counterparts. However, levels of MVICs in this study and the previous literature findings (3) suggest that both types of waves during battle rope training provide enough intensity to enhance core motor control and muscle endurance.
Anterior deltoid muscle activity was high during both wave movements, indicating that it is one the primary muscles involved in the action. However, there was no difference between conditions, which is in accordance with the study by Santana et al. (23), who found the same muscle activity during the standing unilateral cable press than during the bench press. Higher stability requirements during the performance of an exercise where the AD has a primary mover role seem to provide at least the same muscle activity compared with more unstable conditions as has been reported during stable vs. unstable push-ups (11) or during suspended push-ups when the participants used the most stable device (5).
Unilateral exercises have been recommended to activate hip muscles (2). For example, a single-leg squat was more effective than the double-leg squat for activating GM (16). Despite a tendency was observed, GM activity showed no difference between conditions in our study. The GM muscle stabilizes the femur and pelvis during weight-bearing activities (2,21), providing multiplanar stabilization for the trunk/pelvis (21). The bipedal stance and the maintained hip position that we used in this study during the performance of both exercises could be the main reasons for the absence of muscle activity differences. It seems that this muscle is less affected by upper body unilateral and bilateral movements when a bipedal stance is performed. Hence, it is probable that the GM muscle activity that we found is mostly produced because of the stabilizer rather than primary mover role of the muscle as demonstrated in the %MVIC values, which were the lowest in the study.
The length and diameter of the ropes, the velocity and amplitude of the waves (18), and the weight of the ropes determine the amount of intensity during the battle rope exercise. As optimal loads should be calculated for each different exercise to provide the correct intensity and induce positive training adaptations, the use of the battle ropes imply the use of the same weight, length, and diameter of the ropes for everyone. Because of the own properties of the rope, there is no option to individualize the load for each condition, so the exercise was assessed as is usually performed by practitioners, providing a real transference of the results to the usual training situation. However, ropes of differing weight, length, and diameter could have different EMG results.
This study was established in a cohort of young healthy individuals with previous resistance training experience and thus caution should be taken when generalize findings to different populations. Future studies should investigate additional neuromuscular effects of using battle rope training during different exercises and loads and also evaluate chronic adaptations.
Practical Applications
Our results support the use of battle rope exercises to stress upper body muscles and support that unilateral movements may provide a different training stimulus. Data provided on muscle activity should serve as valuable information to improve the effectiveness of the workout or the training program when battle rope exercises are performed. Coaches and practitioners should be aware that both types of waves provide the same stimulus for AD and GM muscles. However, when high OBLIQ muscle activity is desired, unilateral wave movements should be used. On the contrary, bilateral waves are more proper when the purpose is to stress LUMB muscle. Both bilateral and unilateral wave movements can be used to provide variations during a single training session or a periodized training program.
Acknowledgments
The authors thank the participants for their contribution and Bruno Manjol for their assistance during the data collection.
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