The most common method to increase upper body strength among athletes and recreational lifters is the use of resistance training. Among the most popular exercises in resistance training programs is the bench press. Used as both a test to measure upper body strength and as one of 3 lifts performed in the sport of powerlifting, the bench press is the focus for many athletes looking to increase upper body strength. Due to its popularity, the bench press has many different forms that are incorporated into various training programs, including inclination of the bench (3) use of machines (16,21,22,2316,21,22,2316,21,22,2316,21,22,23), chains (6,176,17), and bands (1,5,6,241,5,6,241,5,6,241,5,6,24). Another method is an unstable surface (2,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,26) designed to not only work on strength but also add trunk stabilization to the exercise (2,7,11,15,262,7,11,15,262,7,11,15,262,7,11,15,262,7,11,15,26).
Owing to its popularity, previous research has examined the effects of different bench press variations and their possible benefits. The common use of a Swiss ball bench press has led some researchers to study the effect unstable surfaces have on muscle activity (2,4,7,11,15,25,262,4,7,11,15,25,262,4,7,11,15,25,262,4,7,11,15,25,262,4,7,11,15,25,262,4,7,11,15,25,262,4,7,11,15,25,26) and max force production (2,4,7,13,252,4,7,13,252,4,7,13,252,4,7,13,252,4,7,13,25). However, the use of an unstable surface is not the only way individuals have added variety to resistance training to increase upper-body strength. Another technique that has gained popularity in recent years is use of an unstable load (UL), commonly called the chaos bench press, for both strength gains and shoulder rehabilitation. Recently, a study investigating an UL in the squat showed significantly greater muscle activation of the rectus abdominus, external oblique, and soleus with a slight decrease in vertical ground reaction force compared with a stable load (SL) (14). However, these effects on muscle activation in the bench press are unknown.
Although the use of a Swiss ball has been shown to increase trunk stabilizer and anterior deltoid muscle activity (2,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,262,7,9,13,15,25,26), it has not been shown to have an effect on maximum force production (2,4,7,13,252,4,7,13,252,4,7,13,252,4,7,13,252,4,7,13,25). However, little to no research has examined the chronic effects of incorporating an unstable surface into a resistance training program. The use of chains and bands has been shown to have a positive effect on strength gains in acute training (1,51,5), but little is known about the chronic effects. With previous research showing greater muscle activation with an unstable surface (10,12,1510,12,1510,12,15), the use of an UL, added to an already unstable barbell, during a bench press to illicit greater muscle activation to increase upper-body strength may have some merit. Therefore, the purpose of this study was to examine upper body muscle activation during the bench press exercise between SLs and ULs with both a high-intensity and low-intensity load. We hypothesized that the use of an UL would show greater upper body muscle activation when compared with a SL.
Experimental Approach to the Problem
In order to analyze muscle activation, 20 participants performed the bench press with a SL and UL at both 60 and 80% 1 repetition maximum (1RM). Unstable loads were created using elastic bands and a pair of 16 kg kettlebells. Electromyography of 5 muscles (pectoralis major, anterior deltoid, medial deltoid, triceps brachii, and latissimus dorsi [LD]) was recorded and compared among conditions.
Twenty trained (≥1 year of resistance training experience) men (age = 24.1 ± 2.05 years, age range = 22–28 years, height = 177.5 ± 5.76 cm, mass = 88.7 ± 13.72 kg) with no upper-body injuries within the last year volunteered to participate (20). They were able to bench press at least their body weight for 1RM (126.4 ± 15.5 kg) and greater than 86.4 kg to accommodate the minimum weight of the kettlebells. All subjects read and signed a University IRB-approved informed consent form before testing began. Subjects were instructed to maintain their regular diet, not to consume supplements and abstain from performing upper-body resistance training throughout testing.
Height and mass were recorded using a scale (ES200L; Ohaus Corporation, Pinebrook, NJ, USA) and stadiometer (Seca, Ontario, CA, USA) before testing. On the first visit, they were measured for their stable bench press 1RM to determine the weight used during experimental trials. Warm-up consisted of 2 sets of 6 reps at 50% estimated 1RM and 3 reps at 80% with 3-minute rest between sets (7,187,18). Subjects used a self-selected grip width that was maintained for both 1RM testing and during trials. They maintained 5 points of contact (back of head, shoulder blades, buttocks, and left and right foot) for 1RM and all trials. A slight pause was required at the bottom of the lift so no bouncing would occur (8). First attempt was at 90% of estimated 1RM, with increases of no more than 15% of the previous attempt, so a 1RM was achieved within 5 attempts. If they failed to lift the desired weight, it was reduced by 2–5%. After 1RM testing, familiarization was performed by having subjects practice the bench press with an UL with 2 sets of 3 lifts with a 2-second cadence. All subjects used a standard barbell with 16-kg kettlebells attached by elastic bands (one on each end; Figure 1). Subjects returned a week later to perform 2 experimental trials on 2 different days with 48-hour rest (23). All trials were counterbalanced with the first subject flipping a coin to determine which condition and intensity they performed. Intensity order was maintained in the second condition.
On the first trial, subjects were fitted with electrodes and performed an isometric bench press (ICCs ranged from 0.83 to 0.96), for electromyographic (EMG) normalization, with the bar set to a height where the upper arm was parallel to the ground. Unstable load trials used 16-kg kettlebells suspended by elastic bands (41″ × 0.5″ × 4.5 mm; Rogue Fitness, Columbus, OH, USA) from the barbell with extra weight added to the bar to achieve the proper weight. Low-intensity trials used 60% 1RM (average weight from kettlebells = 21.4% ± 2.5, 15.6–26.0%), and high-intensity used 80% 1RM (average weight from kettlebells = 16.0% ± 1.8, 11.7–19.0%).
Each trial consisted of 3 single concentric and eccentric repetitions at both intensities (ICCs ranged from 0.92 to 0.97). During UL trials, elastic bands were placed 20 cm from the end of the bar sleeve. The bands were doubled and threaded through the kettlebell handle then slid on to the sleeve of the bar. For each repetition, subjects were given a lift-off and few seconds to gain control of the weight. A 2-second cadence was used for eccentric and concentric actions. Subjects were given a command to lower at the top and to lift at the bottom to prevent bouncing and to insure the weight was under control before starting the rep. A velocity transducer (V80-L7-M; Unimeasure, Corvallis, OR, USA) was attached to one end of the barbell to distinguish between concentric and eccentric muscle actions. All data were recorded and analyzed using custom LabVIEW software (version 2013; National Instruments, Austin, TX, USA).
Subjects were fitted with 5 separate bipolar (3.5 cm center-to-center) surface electrodes (EL500 silver-silver chloride; BIOPAC Systems, Inc., Goleta, CA, USA) after shaving the area, abrading the skin, and cleaning with an isopropyl alcohol pad (26). Electrodes were placed longitudinally on the muscle belly away from tendons on the pectoralis major, anterior deltoid, medial deltoid, triceps brachii, and LD. Placement was 2 cm horizontally from the axillary fold on the pectoralis major sternocostal head, 4 cm from the clavicle placed parallel to the anterior deltoid, 3 cm below the acromion placed parallel to the medial deltoid, halfway between the acromion and olecranon process running parallel to the triceps brachii long head 2 cm medially from the midline, and 4 cm from the inferior tip of the scapula running parallel with the LD. Placement on the LD were roughly 3/4 the distance laterally from the spine to prevent subjects from lying on them during trials.
EMG signals were filtered (fourth-order Butterworth, 10–500 Hz) and preamplified using a differential amplifier (Myopac MPRD-101; Run Technologies, Mission Viejo, CA, USA; bandwidth = 1–500 Hz) with a sampling frequency of 1,000 Hz (26).
Before statistical analyses, subjects' EMG amplitude (root mean square) was normalized to their isometric bench press data. The data were then analyzed using a 2 × 2 × 2 × 5 (condition × intensity × action × muscle) analysis of variance (ANOVA) and then followed up with simple ANOVAs. An alpha level of 0.05 was used for statistical significance, and SPSS version 21.0 software (SPSS, Inc., Chicago, IL, USA) was used for all analyses.
There was no significant 4-way interaction (Table 1), but there was a significant 3-way interaction of intensity × action × muscle. This was followed up with five 2-way ANOVAs (action × intensity), one for each muscle. All muscles had a significant interaction. These were followed up with ten 1 × 2 ANOVAs. For all 5 muscles, low-intensity concentric, high-intensity eccentric, and high-intensity concentric were significantly greater than low-intensity eccentric. Also, high-intensity concentric was significantly greater than low-intensity concentric (Figure 2).
The purpose of this study was to examine muscle activation of the upper body musculature during a bench press exercise between SL and ULs and between high and low intensities. Our results demonstrated that there were no significant differences between SL and UL. Therefore, it seems that the use of either an UL or SL confers no advantage or disadvantage relative to upper body muscle activation. Possible factors for this lack of difference could include measurement of only prime movers, intensity, or level of instability.
Our results are typical regarding muscle activation between high and low intensities (16,19,2316,19,2316,19,23) and also eccentric and concentric muscle actions (6,16,21,266,16,21,266,16,21,266,16,21,26). Interestingly, muscle activation of the LD was significantly greater at the higher intensity, which may provide evidence that the LD is a secondary muscle used in the bench press. To our knowledge, this is the first study to examine activation of the LD during the bench press at 2 separate intensities. Owing to the LD role as an adductor of the humerus, it may assist as an important synergist in this movement keeping the elbows tucked into the body during the concentric portion of the lift.
When examining shoulder stability, McCaw and Friday noted that a higher intensity (80%) increased joint stiffness, eliminating the need for the anterior and medial deltoid to work against external rotation and adduction of the humerus (16). The primary reason for testing at 2 intensities in this study was to determine whether the use of an UL would have an effect on muscle activation at a higher intensity. Our results showed no difference between load stability and intensity. Studies that looked at machine and free weight bench press have seen a significant increase in muscle activation of the anterior (16,2116,21) and medial deltoid (16,2316,23) at high intensities. The use of a Chest press or Smith machine showed lower activation of both the anterior and medial deltoid muscles compared with free weights because of having a fixed position only allowing the bar to move in one plane (16,2316,23).
It is also possible that the use of an absolute load to create instability was not as effective as a relative load or ineffective all together. Although we used an absolute load, the average suspended weight was ∼21% of the total weight at 60 and ∼16% at 80%. The use of an absolute load allowed for more control over the tension on the band, but the use of multiple types of bands and kettlebells could lead to different results. Although the use of an UL does seem to require greater muscle activation for stabilization, it is possible that its use is only effective for those who lack the general stability that comes with regular free weight resistance training. Since we used only experienced lifters, our UL may not have been unstable enough to elicit greater muscle activation.
The lack of significant differences in muscle activation between stable and unstable bench press may allow the use of ULs by practitioners to add variety to resistance training programs. Also, since some sports, such as football, require the movement of unstable objects, the use of instability in training may provide a more specific stimulus then stable. However, a lack of difference between conditions in this study demonstrates that there seems to be no advantage or disadvantage to the use of an UL in the bench press.
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