Exercise choice is a critical variable that strength and conditioning professionals must take into consideration when designing resistance training programs (3). Exercise mode can be manipulated by changing body posture, number of muscles used (single- or multi-joint exercises), grip, width of hands and feet, range of motion, or type of device with different stability requirements (i.e., free weights, machines, elastic bands, etc.) (3,4,13). These variations provide several options to design resistance training programs. Consequently, preview studies have evaluated the effects of different modes of resistance exercise on acute and chronic responses to strength training (3,20,26).
Free weight and machine exercises require distinct movement control (15,26). Free weights must be stabilized in the transverse, coronal, and sagittal planes, whereas machines use unidirectional guided movements (15,26,28). These differences in stability requirements influence muscle force production and neuromuscular activity (12,15,20–22,26,28). It has been observed that higher loads can be lifted in the squat when using a Smith machine compared with free weights (12), whereas muscle activation is 34, 26, and 49% less in the gastrocnemius, biceps femoris, and vastus medialis, respectively, using a Smith machine (22). Conversely, studies have found higher loads lifted and higher muscle activation with a free weight barbell chest press when compared with a Smith machine (15,21,26). There also appears to be a difference within free weight exercises because of stabilization requirements. Muscular force production in a dumbbell chest press has been shown to be 17% less when compared with a barbell, whereas muscle activation was higher with dumbbells (20). These results indicate that levels of physiological stress and mechanical strain may be different between free weights and machines for the same muscle group.
Muscle performance may be temporarily reduced for minutes, hours, or several days after resistance exercise (5). This reduction is partially due to the physiological stress and mechanical strain on muscle tissue given the volume and intensity during heavy resistance exercise. Longer-lasting impairment in muscle function characterized by a reduction in range of motion, an increase in inflammatory response, muscle swelling, and delayed onset muscle soreness is termed as exercise-induced muscle damage (5,10,19). Accordingly, the time course of muscle damage recovery is an important factor that can affect the volume and intensity of subsequent training sessions. In addition, an optimal balance between training stimulus and recovery is essential to avoid overtraining and maximize training adaptations (5,8).
Investigating the effects of exercise with different stability requirements on the time course of muscle damage recovery may help strength and conditioning professionals to better design strength training programs across periodization cycles. However, to the best of the authors' knowledge, there are no studies that have investigated this on the long-term time course of muscle recovery (up to 96 hours) in resistance-trained men. We hypothesized that using barbells would result in higher muscle damage and a longer recovery. The rationale for this is based on the higher load lifted during a barbell chest press than with a machine or dumbbells (20,26), as the magnitude of muscle damage seems to be associated with exercise load (6,9). Therefore, the purpose of this study was to compare the time course of muscle damage recovery between 3 modes of chest press exercise with different stability requirements in resistance-trained men.
Experimental Approach to the Problem
Volunteers were randomly assigned, using a random number table, into one of the 3 groups: (a) Smith machine bench press, (b) barbell bench press, or (c) dumbbell bench press. To avoid the repeated bout effect on muscle damage levels and the time course of recovery, the groups were independent and each volunteer only participated in one of the 3 groups. Participants came to the laboratory on 7 occasions. The first visit consisted of familiarization with the experimental procedures and anthropometric and velocity-controlled 10 repetition maximum (RM) load assessments. On the second visit, after 72 hours, a velocity-controlled 10RM re-test was performed. On the third visit, 72 hours after the second, volunteers performed their specific exercise training protocol. Indirect markers of muscle damage were assessed before (pre), immediately after, 24, 48, 72, and 96 hours after the training protocol. To minimize circadian influences, subjects visited the laboratory at the same time each day. Volunteers were instructed to not engage in any vigorous physical activity or unaccustomed exercise and to not take medications or food supplements during the entire study period.
Twenty-seven resistance-trained men (age: 23.5 ± 3.8 years [ranging from 18 to 34 years]; height: 175 ± 6.0 cm; mass: 80.11 ± 7.54 kg) volunteered to participate (Table 1). Volunteers had to be involved with strength training for at least 1 year (4.36 ± 3.12 years) without interruption to be included in the study. In addition, they had to have a bench press 1RM higher than their body weight. Participants were excluded if they had any history of neuromuscular, metabolic, hormonal, or cardiovascular disease or if they were taking any medication that could influence hormonal or neuromuscular function. Participants were informed about the design and experimental procedures of the study and all possible risks and discomforts related to the procedures. They all signed an informed consent form approved by the local institutional review board and was performed in accordance with the Declaration of Helsinki.
Velocity-Controlled 10 Repetition Maximum Assessment
The load used by each training group was determined by velocity-controlled 10RM testing according to Kraemer and Fry (14). Each group was tested according to their specific exercise, and the load was adjusted with weight plates starting at 1 kg. Volunteers warmed up by performing 10 repetitions at 40% of their estimated 10RM, then 10 repetitions at 60%, with 60 seconds of rest. Finally, their velocity-controlled 10RM load was determined with no more than 3 attempts with 5 minutes of rest between attempts. An electronic metronome was used to control the velocity of each repetition, with 1–2 seconds for the concentric and 2–3 seconds for the eccentric phase.
The training protocols were composed of 8 sets of 10 repetitions with 2 minutes of rest between sets. To avoid a severe drop in the number of repetitions, the initial load was 90% of 10RM. Moreover, in the fourth set, the load was reduced by 20%. Each repetition lasted approximately 4 seconds, with 1–2 seconds for the concentric and 2–3 seconds for the eccentric phase. Range of motion was also controlled for all groups so that for the eccentric phase, they had to touch their chest and return to a position with their elbows fully extended at the end of the concentric phase. During the dumbbell chest press, a plastic stick was placed in each dumbbell bar and the sticks had to touch the chest at the end of the eccentric phase. In addition, their neck, head, shoulders, and hips were kept in contact with the bench throughout the exercise, with their feet on the floor.
Muscle Thickness Assessment
Muscle thickness of the right pectoralis major and triceps brachii were measured by ultrasonography using B-Mode ultrasound (Model BF; Philips-VMI, Ultra Vision Flip, New York, NY, USA). A water-soluble transmission gel was applied to the measurement site, and a 7.5-MHz ultrasound probe was placed perpendicular to the surface, without depressing the skin. Volunteers were measured supine for the pectoralis major and prone for the triceps brachii, after resting 5 minutes. The pectoralis major was measured at the point between the third and fourth rib under the midpoint of the clavicle (29). Triceps brachii was measured at 60% of the distance from the acromial process of the scapula to the lateral epicondyle of the humerus (29). Once the technician was satisfied with the quality of the image, it was frozen on the monitor (7) then digitized and later analyzed with Image-J software (Version 1.37; National Institute of Health, Bethesda, MD, USA). The measurement area was marked at baseline to assure that the same location was assessed at each time point. Volunteers were asked to not clean the mark. Muscle thickness was calculated as the distance from the subcutaneous adipose tissue-muscle interface to the muscle-bone interface (1).
Peak Torque Assessment
Unilateral peak torque of the shoulder horizontal adductors and elbow extensors were measured by an isokinetic dynamometer (Biodex Medical, Inc., Shirley, NY, USA). Volunteers performed 2 sets of 4 repetitions at 60° per second for each exercise with 2 minutes of rest between sets. For shoulder horizontal adduction, volunteers were positioned supine with belts fastened across their trunk, pelvis, and calf to minimize extraneous body movements (Figure 1). The acromial process was used as a marker to align the shoulder with the dynamometer's lever arm, allowing a physiological range of motion from 90° of horizontal abduction to 0° of horizontal adduction (90° total range of motion). These procedures were in accordance with work by Silva et al. (23).
For the elbow extensors, volunteers were seated with their arms placed over a Scott Bench positioned close to the dynamometer, allowing a range of motion from 125° flexion to 5° of extension (120° total range of motion; Figure 2). The lateral epicondyle of the humerus was used to align elbow rotation to the dynamometer's lever arm. The forearm remained in a neutral position throughout the test. Gravity correction was obtained by measuring the torque exerted by the lever arm and the participant's relaxed arm at full extension for both tests. Values for the isokinetic variables were automatically adjusted for gravity by the Biodex Advantage software. Researchers provided verbal encouragement during all tests. Maximal peak torque was defined as the highest torque value (N·m) recorded during the 2 sets.
Muscle Soreness and Subjective Perception of Muscular Fatigue and Recovery
Muscle soreness of the pectoralis major and triceps brachii were assessed using a 100-mm visual analog scale with “no soreness” (0 mm) on one end and “severe soreness” (100 mm) on the other. Volunteers rated their muscle soreness when the muscle was palpated by the examiner, who applied pressure to the medial part of the pectoralis major and triceps brachii with the third and fourth finger for approximately 3 seconds (27). The same examiner performed all test procedures for all subjects.
To measure subjective perceived muscular fatigue and recovery, subjects rated their perception of physical fitness using a visual analog scale from 0 to 120 mm, where 0 mm was maximum fatigue and not recovered and 100 mm was maximal physical fitness recovery, compared to their fitness the week before the training protocol (2).
Data are presented as mean ± standard deviation. The Shapiro-Wilk test was used to check for a normal distribution. Taking into account that peak torque and muscle thickness data were normally distributed, a 2-way 3 × 6 (group [Smith machine, barbell and dumbbell] × time [pre, immediately post, 24, 48, 72, and 96 hours after exercise]) mixed factor analysis of variance (ANOVA) was used to analyze peak torque and muscle thickness. Physical characteristics were analyzed by one-way ANOVA, and training volume differences were analyzed by 2-way (3 groups × 8 training sets) mixed factor ANOVA. In the case of significant differences, a Fisher's least significant difference post hoc test was used. As muscle soreness and subjective physical fitness data did not present a normal distribution, the nonparametric Mann-Whitney (between groups) and Friedman (within group) tests were used to analyze these variables. The significance level was set a priori at p ≤ 0.05. Reliability of all measurements was calculated by intraclass correlation coefficient (ICC) values using single values. In addition, the effect size calculation was used to determine the magnitude of each condition effect. Cohen's (11) ranges of 0.1, 0.25, and 0.4 were used to define small, medium, and large ƒ values, respectively. SPSS software (version 17.0; SPSS, Inc., Chicago, IL, USA) was used for all data analyses.
Training Performance and Physical Characteristics
Physical characteristics and training status were not different between groups (p > 0.05, Table 1). Test-retest reliability ICCs for the Smith machine, barbell, and dumbbell 10RM tests were 0.96, 0.97, and 0.89, respectively. The load lifted by the dumbbell group (62.8 ± 9.5 kg) was 18.6% lower than the barbell group (74.5 ± 12.5 kg, p = 0.042) and 15.2% lower than the Smith machine group (72.4 ± 9.7 kg, p = 0.05). However, the total amount of weight lifted during each training protocol (10RM loading) did not differ between the Smith machine (14,218.0 ± 3743.0 kg), barbell (14,411.0 ± 3986.9 kg), and dumbbell groups (12,077.0 ± 2915.0 kg) (F = 3.0, p = 0.69). In addition, there was no difference between groups for the number of repetitions performed (F = 0.81, p = 0.64; Figure 3).
Time Course Recovery of Shoulder Horizontal Adductors
Test-retest reliability ICCs for peak torque, muscle thickness, and muscle soreness of the triceps brachii were 0.93, 0.93, and 0.86, respectively. Peak torque of the shoulder horizontal adductors decreased immediately after resistance exercise with no differences between groups (17.1% for the Smith machine, 16.3% for the barbell, and 16.9% for the dumbbell, p = 0.94). In addition, there was no significant group-by-time interaction for shoulder horizontal adductors peak torque (F = 0.43, p = 0.93, power = 0.22, ƒ = 0.2) (Figure 4) or pectoralis major muscle thickness (F = 0.26, p = 0.98, power = 0.11, ƒ = 0.15) (Figure 5). There were also no significant main effects for group for peak torque (F = 0.31, p = 0.74, power = 0.09) or muscle thickness (F = 0.13, p = 0.88, power = 0.07). However, there were significant main effects for time for peak torque (F = 30.11, p < 0.001, power = 1) and muscle thickness (F = 19.02, p < 0.001, power = 1). Each group recovered their shoulder horizontal adductor peak torque by 72 hours after the exercise protocol (p > 0.05), whereas pectoralis major muscle thickness returned to baseline by 24 hours for all groups (p > 0.05).
There was no difference in pectoralis major muscle soreness between groups (p > 0.05, ƒ = 0.11; Figure 6). All groups recovered by 96 hours (Smith machine; χ2 = 29.08, p < 0.001; barbell: χ2 = 31.05, p < 0.001; dumbbell: χ2 = 32.05, p < 0.001).
Time Course Recovery of the Elbow Extensors
Test-retest reliability ICCs for peak torque, muscle thickness, and muscle soreness of the pectoralis major was 0.96. Time course recovery of the elbow extensors is presented in Table 2. There were no significant group-by-time interactions for elbow extensor peak torque (F = 1.63, p = 0.11, power = 0.24, ƒ = 0.38) or muscle thickness (F = 0.48, p = 0.90, power = 0.19, ƒ = 0.2). There were also no significant main effects for group for elbow extensor peak torque (F = 0.66, p = 0.52, power = 0.18) or muscle thickness (F = 2.08, p = 0.15, power = 0.38). However, there were main effects for time for elbow extensor peak torque (F = 14.99, p = 0.001, power = 0.96) and muscle thickness (F = 35.64, p < 0.001, power = 1). All groups recovered their elbow extensor peak torque by 48 hours (p > 0.05), whereas triceps brachii muscle thickness returned to baseline by 24 hours (p > 0.05).
The Smith machine and barbell groups recovered from elbow extensor muscle soreness by 72 hours (Smith machine; χ2 = 17.49, p = 0.002; barbell: χ2 = 22.46, p < 0.001), whereas the dumbbell group did not change throughout the entire 96 hours (χ2 = 11.84, p = 0.06). Moreover, muscle soreness was higher in the barbell group at 24 and 48 hours when compared with the dumbbell group (p ≤ 0.05). The effect size was medium (ƒ = 0.25).
Time Course Recovery of Subjective Physical Fitness Recovery
For subjective perception of training, the Smith machine and dumbbell groups recovered by 72 hours (Smith machine; χ2 = 22.67, p < 0.001; dumbbell: χ2 = 25.41, p < 0.001) (Figure 7), but the barbell group did not recover till 96 hours (χ2 = 31.33, p < 0.001). Finally, subjective physical fitness recovery was higher in the dumbbell group at 24 and 72 hours when than in the barbell group (p ≤ 0.05). The effect size was small (ƒ = 0.18).
Tracking the time course of muscle recovery is an important consideration when designing periodized resistance training programs, especially in high-level sports, such as competitive weightlifting, powerlifting, and bodybuilding, because of its known negative relationship with workload, training volume (5,8), and subsequent training stimulus. Thus, the purpose of this study was to compare the time course of muscle damage recovery between 3 modes of chest press exercise with different stability requirements in resistance-trained men. Our initial hypothesis was not confirmed, as there were no differences between groups in recovery time or muscle thickness. However, when examining the 2 free weight modes (barbell vs. dumbbell), elbow extensor muscle soreness of the barbell group was higher and took longer to recover than the Smith machine and dumbbell groups. In addition, despite similar muscle strength recovery of the shoulder horizontal adductors and elbow extensors, the barbell group demonstrated lower readiness (i.e., subjective perception of physical fitness) for training than the other 2 groups.
Several studies have shown higher force production during free weight bench press than a Smith machine bench press (12,20,26). Saeterbakken et al. (20) observed that muscle strength (1RM) in a horizontal barbell chest press was 3% higher than that for a Smith machine and 17% higher than that for a dumbbell chest press. In addition, muscle strength of a dumbbell chest press was 14% less than for a Smith machine. These results are consistent with research by Tillaar et al. (26), who found that the highest 1RM chest press strength was performed in the barbell chest press (106.4 ± 15.5 kg), followed by the Smith machine (103.6 ± 14.8 kg) then dumbbells (89.5 ± 13.7 kg). Another study also reported greater 1RM strength in the barbell chest press in comparison with the Smith machine (12). Although the present study did not show significant differences in training volume between groups, our results are somewhat in agreement with those of previous studies, because the load lifted (10RM) by the dumbbell group was 18.6% lower than the barbell group and 15.2% lower than the Smith machine group.
The magnitude of muscle damage caused by each exercise in this study was in accordance with previous studies that have evaluated muscle recovery after chest press exercise in trained men (16,27). Meneghel et al. (16) investigated changes in indirect markers of muscle damage after 2 bouts of free weight eccentric bench press performed by resistance-trained men. Their participants performed 4 sets of 8 eccentric actions (3 seconds for each repetition) at 70% of their eccentric 1RM with 2 minutes of rest between sets. Similar to this study, they reported a reduction of 10% in 1RM strength and peak muscle soreness of 3.8 mm after exercise. The results reported by Soares et al. (24) also corroborate our findings on the time course of recovery of the elbow extensors after a multijoint exercise. They observed that elbow flexor peak torque recovered at 24 and 72 hours after multijoint exercise (seated row machine), in which elbow flexors were recruited as synergist muscles. Thus, according to Paulsen et al. (19), the muscle damage caused by each exercise in this study could be considered moderate, as overall, volunteers took 72 hours to recover.
As this is the first study to compare the effects of a Smith machine, barbell, and dumbbell chest press on the time course of muscle recovery, the present findings cannot be directly compared with previous studies. Taking into account the fact that resistance load can affect muscle damage recovery (17,18,25), it was expected that the higher load in the barbell chest press reported by previous studies (12,20,26) would result in higher muscle damage. However, besides difference in load between modes in this study, the volume lifted throughout the 8 sets was similar between groups. These results are consistent with Uchida et al. (27) who compared the effects of 4 different intensities of bench press on indirect markers of muscle damage. They tested trained men with 5 intensities: (a) 50% (1RM), (b) 75%, (c) 90%, (d) 110%, and (e) control, whereas total volume was matched between groups. Muscle soreness and plasma creatine kinase levels were not significantly different between groups after exercise. According to the authors, the intensity of the bench press exercise did not affect the magnitude of muscle soreness or blood markers of muscle damage. Thus, it appears that training volume has an important influence on exercise-induced muscle damage independent of instability and load requirements for the same muscle group. However, this topic requires further investigation.
The Smith machine and barbell groups recovered from elbow extensor soreness 48 hours after exercise, whereas the dumbbell group did not present any muscle soreness at all. This difference may be related to the stability requirements of each exercise. Increased stability is required with dumbbells compared with barbells, which is most likely because of the separate movement of the elbow joint, which can increase instability in the frontal and sagittal planes, thus shifting the muscle activation pattern (26). Higher muscle activation in the elbow flexors has been seen in the chest press with different stability requirements (dumbbell higher than barbell), whereas higher elbow extensor activity was observed in a barbell than in a dumbbell chest press (20,26). Thus, the load imposed on elbow flexors (i.e., biceps) may be greater with dumbbells than with a barbell, leading to a distinct and specific time course of muscle soreness recovery.
Another interesting result of the present study was that the subjective perception of physical fitness (Figure 7) was higher in the barbell than the dumbbell group. The barbell group took up to 96 hours to recover, whereas the Smith machine and dumbbell groups took 72 hours. These results may suggest that the barbell imposed a higher physiological demand and are similar to those of Ahtiainen et al. (2) where their trained volunteers took up to 144 hours to recover from 5 sets of 10RM leg press and 4 sets of 10RM squat exercises. However, these findings require further investigation. Moreover, the present study is not without limitation as muscular enzymes and biochemical inflammatory markers were not measured. In addition, only young resistance-trained men were evaluated.
In conclusion, different modes of chest press exercise required similar recovery time for peak torque and muscle thickness in the shoulder horizontal adductors and elbow extensors. In addition, pectoralis muscle soreness recovery was not different between modes. However, the time course of elbow extensor muscle soreness recovery was greater after barbell compared with dumbbell exercise. Whether the similar muscle recovery observed in the present study would result in similar muscle adaptations remains unknown. Thus, further study is necessary to understand what effects free weights vs. machines have on muscle strength and hypertrophy gains. It is also important to evaluate muscle damage recovery in other populations, such as untrained volunteers, women, and the elderly.
The results of the current study suggest that coaches and strength professionals can expect similar muscle damage recovery after Smith machine, barbell, or dumbbell chest press resistance exercise in trained men. However, they might not be able to perform strength training at their maximal intensity until 72 hours after 10RM dumbbell or Smith machine and 96 hours after barbell bench press. Thus, strength and conditioning professionals should consider focusing on regenerative training or lower load protocols, such as muscle power or muscular endurance training, during the recovery period after heavy resistance exercise when maximal muscle force remains reduced. In addition, they can target other muscle groups during this recovery time.
This study received no external funding. The authors declare no conflicts of interest. The results of the present study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association.
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