An intraclass correlation coefficient (ICC3,1) was used to estimate the test-retest reliability of the EMG recordings. A 1-factor repeated measures analysis of variance (ANOVA) with Bonferroni corrections addressed question 1 whereby we examined differences in EMG activation (%MVIC) for a specific muscle group among the 3 exercise conditions. Similarly, a 1-factor repeated-measures ANOVA with Bonferroni corrections also addressed question 2 where we compared the absolute elbow joint ROM across the 3 exercise conditions. Lastly, question 3 explored the temporal sequence of muscle activation for each of the 3 exercise conditions and was tested with a repeated-measures (3 conditions × 7 muscles) ANOVA. Post hoc analysis of the condition × muscle interaction on timing of peak muscle activation as a percentage of the complete pull-up cycle was performed. Simple effects tests with Bonferroni correction were used to handle multiple comparisons. For all 3 ANOVAs, we used a level of significance of p ≤ 0.05. All data were analyzed with SPSS 15.0 for Windows software (SPSS Inc, Chicago, IL, USA).
During the pull-up test-retest procedure, EMG recordings from 8 subjects were separated by 2 weeks. The ICCs for the 7 muscles were as follows: (a) infraspinatus-0.77; (b) biceps brachii-0.64; (c) lower trapezius-0.64; (d) external oblique-0.57; (e) erector spinae-0.48; (f) latissimus dorsi-0.35; and (f) pectoralis major-0.35.
Electromyographic Exercise Data
During the concentric phase, statistically significant differences existed between the conventional pull-up and the chin-up exercises as follows: (a) the lower trapezius had greater activation (p = 0.006) in the conventional pull-up when compared to the chin-up (mean difference = 10.8% MVIC, 95% confidence interval [CI] = 2.8-18.8% MVIC, effect size = 0.51); (b) the pectoralis major had greater activation (p = 0.009) in the chin-up when compared to the pull-up (mean difference = 13.6% MVIC, 95% CI = 3.0-24.3% MVIC, effect size = 0.3); and (c) the biceps brachii had greater activation (p = 0.03) in the chin-up when compared to the pull-up (mean difference = 17.9% MVIC, 95% CI = 1.5-34.2% MVIC, effect size = 0.54). Values of mean peak activation (percentage) data for the 3 exercise conditions are contained in Figure 6.
Elbow Joint Range of Motion Data
During the concentric phase, we observed a statistically significant difference in absolute elbow joint sagittal plane ROM among the 3 pull-up/chin-up exercises (F2,30 = 4.13, p = 0.03); however, Bonferroni tests for multiple comparisons did not detect significant pairwise differences (Figure 7). Mean absolute elbow joint ROM was 93.4 ± 14.6°, 100.6 ± 14.5°, and 99.8 ± 11.7° for the pull-up, chin-up, and combined pull-up/chin-up performed using the Perfect·Pullup™ twisting handles, respectively.
Muscle Recruitment during the 3 Exercises
The temporal order of peak motor unit recruitment was visualized from RMS processed EMG data to determine the temporal sequence of selected back, shoulder, arm, and abdominal muscles during the complete pull-up cycle for each of the 3 conditions. Timing of peak EMG activation was expressed as a percentage of a complete pull-up, chin-up, or rotational exercise cycle using the Perfect·Pullup™ twisting handles. A repeated measures (3 conditions × 7 muscles) ANOVA detected a statistically significant muscle × conditions interaction (F2,276 = 2.83, p = 0.021), which indicated the presence of differences in the order of peak activation among the pull-up conditions. Sequential muscle activation expressed as a percentage of the complete pull-up cycle and the results of multiple comparisons are displayed in Figures 7-9 for the pull-up, chin-up, and combined pull-up/chin-up using the Perfect·Pullup™ twisting handles, respectively. On average (Figure 10) a complete cycle for each of the 3 exercise conditions lasted about 2,500 milliseconds. The midpoint of each exercise cycle occurred at the point of termination of elbow flexion and signified the completion of the concentric or up-phase of the cycle. Additionally, the timing at which peak activation of a muscle occurred ranged from 12% to 44% of the cycle.
To our knowledge, no one has normalized EMG activity for the pull-up/chin-up exercise to % MVIC, so the primary purpose of this study was to compare the magnitude of action of the 7 muscles across the 3 exercise conditions to determine if the pull-up/chin-up mode of exercise influenced muscle recruitment. On the basis of EMG activation data, DiGiovine et al. (12) classified relative muscular demand into 4 categories: low (<20% MVIC), moderate (20-40% MVIC), high (41-60% MVIC), and very high (>60% MVIC). Moreover, the scheme proposed by DiGiovine et al. agreed with other investigators who contended the threshold value for promoting muscle strength gains during therapeutic exercise required muscle activation greater than 50-60% MVIC (1,4,28). Therefore, we chose to use the EMG signal amplitude (%MVIC) as a method to discuss the relative exercise intensity of the back, shoulder, arm, and trunk muscles when comparing a pull-up, chin-up, and rotational exercise using the Perfect·Pullup™ twisting handles.
The external oblique and erector spinae muscles provide muscular-based or “core stability” to the trunk under destabilizing external forces (3). Both the external oblique and erector spinae are classified as extrinsic muscular stabilizers because they attach partially or totally to the ribs and pelvis, which lie outside the vertebral column (29). During the concentric phase the magnitude of EMG activity for the external oblique ranged from 31 ± 24% MVIC for the pull-up to 35 ± 24% MVIC for the chin-up, whereas the magnitude of EMG activity for the erector spinae ranged from 39 ± 31% MVIC for the pull-up to 41 ± 24% for the chin-up. Both external oblique and erector spinae muscles demonstrated moderate muscle activity (30-40% MVIC), but at a level of recruitment that would not be considered appropriate for strength training (1,4,28). During the pull-up and chin-up exercise the external oblique and erector spinae assisted with stabilization of individual spinal segments within the vertebral column and provided a firm base for the superficial back muscles to move the upper extremities (29). Therefore, on the basis of moderate muscle EMG signal amplitude we would consider the pull-up and chin-up exercise to be useful for promoting endurance training of these extrinsic muscular stabilizers of the trunk (15). Similar to this study results, other investigators have reported EMG signal amplitudes less than 40% MVIC and appropriate for endurance training when healthy subjects perform a variety of core rehabilitation exercises (abdominal crunch, supine bridge, lunge, bent-knee sit-up, active hip abduction in side lying, and quadruped arm and lower extremity lift) that activate the external oblique and erector spinae muscles (15,18,19).
The 5 muscles of the shoulder and arm examined in the present study-pectoralis major, lower trapezius, infraspinatus, latissimus dorsi, and biceps brachii,-displayed high to very high muscle activation at a level that would be appropriate for strength training (1,4,28). Activation of the pectoralis major ranged from 44 ± 27% MVIC for the pull-up to 57 ± 36% MVIC for the chin-up. Compared to values from this study, other investigators have recorded larger magnitudes of pectoralis major muscle activation during upper extremity weight-bearing exercise. For example, Townsend et al. (37) found pectoralis major EMG signal amplitudes of 64 ± 63% MVIC and 84 ± 42% MVIC for a conventional push-up and seated press-up, respectively, whereas Cogley et al. (9) reported mean activation of 94 ± 8% MVIC during the concentric phase of a conventional push-up with hands at shoulder width. Similar to the pectoralis major, the lower fibers of the trapezius in this study displayed high muscle activation ranging from 45 ± 22% MVIC for the chin-up to 56 ± 21% MVIC for the pull-up. Other investigators have reported higher values for the lower trapezius using non-weight-bearing exercises. Moseley et al. (27) and Ekstrom et al. (16) both recorded relatively high EMG activity (60 ± 22% MVIC and 63 ± 41% MVIC, respectively) during elevation of the arm in the scapular plane above 120° using dumbbell weights. Myers et al. (28) reported lower trapezius EMG activity of 88 ± 51% MVIC during external rotation of the shoulder against rubber-tubing resistance with both the arm abducted and elbow simultaneously flexed to 90°. Lastly, Ekstrom et al. (16) recorded peak lower trapezius muscle activation (97 ± 16% MVIC) using a dumbbell load during prone arm raise overhead in line with the muscle fibers.
In this study, the infraspinatus muscle developed very high EMG signals that varied from 71 ± 52% MVIC for the rotational exercise using the Perfect·Pullup™ twisting handles to 79 ± 56% MVIC for the pull-up. Reinhold et al. (32) studied common shoulder external rotation exercises and found side-lying external rotation at 0° abduction against dumbbell resistance produced the peak amount of activity (62 ± 13% MVIC) for the infraspinatus muscle. Earlier Townsend et al. (37) reported infraspinatus muscle activation of 88 ± 25% MVIC when healthy subjects performed prone horizontal shoulder abduction in external rotation with the elbow fully extended against dumbbell resistance. Using a weight-bearing upper extremity exercise, Decker et al. (11) discovered that a push-up with a plus activated the infraspinatus muscle at a level of 104 ± 54% MVIC. The plus movement occurred when the performer pushed his or her upper back toward the ceiling at the conclusion of the traditional up-phase of the push-up. The plus movement has been credited for additional recruitment of motor units within the serratus anterior and rotator cuff muscles (37).
The biceps brachii produced very high EMG signals that varied from 78 ± 32% MVIC for the pull-up to 96 ± 34% MVIC for the chin-up. The chin-up exercise generated greater activation of the biceps brachii when compared to the pull-up because the forearm was supinated-palms facing the subject-when gripping the horizontal bar. Movement scientists have reported the biceps brachii muscle develops its maximal EMG signal (7) and peak torque production (31) with simultaneous elbow flexion and supination. Dynamic upper extremity activities requiring elbow flexion have shown a range of EMG activation signals from the biceps brachii. For example, Koukoubis et al. (23). reported EMG signals were 33 ± 12% MVIC when experienced rock climbers performed finger-tip pull-ups with the forearms pronated. DiGiovine et al. (12) documented that skilled baseball pitchers activated the biceps brachii at a value of 44 ± 32% MVIC during the arm acceleration phase of throwing, whereas Ryu et al. (34) recorded biceps brachii activation of 86% MVIC during the acceleration phase of the tennis forehand.
Of the 7 muscles examined in this study during the pull-up and chin-up procedures, the latissimus dorsi clearly developed the greatest EMG signals ranging from 117 ± 46% MVIC for the chin-up to 130 ± 53% MVIC for the rotational exercise using the Perfect·Pullup™ twisting handles. In comparison, during the arm acceleration phase of baseball pitching (12) the latissimus dorsi elicited 88 ± 53% MVIC activation. The push-up plus (11) and press-up (37), both traditional upper extremity weight-bearing exercises, were reported to generate 49 ± 25% MVIC and 55 ± 27% MVIC activation of the latissimus dorsi, respectively. Furthermore, Signorile et al. (35) discovered that a wide grip anterior lat pull-down exercise normalized to a percentage of each subject's 10RM resulted in muscle activation of 108 ± 8% MVIC.
Data from this study revealed a performer of a pull-up, chin-up, or rotational exercise with the Perfect·Pullup™ twisting handles required about 100° of absolute elbow joint sagittal plane ROM to successfully complete the exercise. Using data supplied by Antinori et al. (2), we estimated 9 healthy subjects (5 men and 4 women) required about 120° of absolute elbow sagittal plane motion to execute a pull-up. The discrepancy between kinematic elbow data from the present study and those of Antinori et al. could be attributed to differences in methodology. Our data were captured with a computer-aided Vicon MX motion analysis system, whereas Antorini et al. used a videocamera connected to a videorecorder. Meanwhile, Morrey et al. (26) reported a healthy person required a 100° “functional arc” (30-130°) to accomplish routine activities of daily living. Neither a pull-up nor chin-up would be considered a routine activity of daily living, but performance of the exercise is well within the expected normal sagittal plane elbow joint ROM.
We proposed the following rationale to justify a muscle's peak activation during the temporal sequence of the pull-up and chin-up cycle. All 7 muscles studied displayed EMG activity throughout the duration of the cycle for each exercise condition particularly during the concentric phase. The lower trapezius was activated early in the 3 pull-up/chin-up exercises at an average of 14.7% of the pull-up cycle and a magnitude of recruitment ranging from 45 ± 22% MVIC for the chin-up to 56 ± 21% MVIC for the pull-up. At the start of the concentric phase of the cycle, the scapula is positioned close to maximum upward rotation. With the subject's hand gripping the horizontal bar and the torso suspended from the pull-up and chin-up apparatus, the scapula is relatively fixed when compared to the trunk thus reversing the action of lower trapezius. The oblique inferomedial-directed muscle fiber orientation allows the lower trapezius to assist with elevation of the trunk. Judging by visual observation trunk elevation initiated the exercise cycle in preparation for shoulder adduction.
Overall, the second muscle recruited was the pectoralis major with peak activation occurring at 18.0% of the pull-up cycle and a magnitude of recruitment that ranged from 44 ± 27% MVIC for the pull-up to 57 ± 36% MVIC for the chin-up. According to Jenkins (22), the sternocostal portion of the pectoralis major muscle extends the shoulder at the glenohumeral joint when the arm is in a flexed position, and, therefore, it is reasonable to assume why the pectoralis major is active early in the pull-up or chin-up cycle. This finding is in agreement with the report of Ricci et al. (33) whereby the lower fibers (sternocostal) of the pectoralis major are activated early in the initial thrust of the pull-up cycle.
The erector spinae was recruited at 23.9% of the pull-up cycle with a magnitude of muscle activation that ranged from 39 ± 31% MVIC for the pull-up to 41 ± 24% for the chin-up. The erector spinae served 2 primary purposes during the exercise cycle. As the subject approached the bar during the concentric phase of the pull-up, back extension was necessary to permit the subject's head to clear the horizontal bar. Moreover, the erector spinae also assisted with stabilization of the pelvis which provided the latissimus dorsi a stable fixation site to pull from later in the exercise cycle.
The fourth muscle recruited was the infraspinatus at 29.6% of the cycle with a magnitude of recruitment that varied from 71 ± 52% MVIC for the rotational exercise using the Perfect·Pullup™ twisting handles to 79 ± 56% MVIC for the pull-up. Neumann (29) commented that during a pull-up exercise the infraspinatus functioned as an arm adductor and extensor. Furthermore, the infraspinatus also provided dynamic shoulder stability to centralize the humeral head against the rigidity of the anterior structures of the shoulder (29).
The biceps brachii was the fifth muscle recruited at 32.4% of the pull-up cycle and a magnitude of recruitment that ranged from 78 ± 32% MVIC for the pull-up to 96 ± 34% MVIC for the chin-up. With the forearm complex stabilized as the subject grasped the bar, the biceps brachii flexed the elbow with reverse action by pulling the humerus toward the fixed forearm. In contrast to data from this study, Ricci et al. (33) commented that the biceps brachii was active during the initial thrust of the pull-up exercise, although the muscle was less active during the remainder of the pull-up cycle.
The penultimate muscle to reach peak muscle activation was the external oblique at 36.4% of the pull-up cycle and a magnitude of activation that varied from 31 ± 24% MVIC for the pull-up to 35 ± 24% MVIC for the chin-up. This muscle primarily functioned as a core stabilizer throughout all 3 exercises. We postulated the late activation displayed in the chin-up was a result of relative trunk flexion when subjects elevated their nose above the horizontal bar near the completion of the concentric phase of the exercise cycle.
The last muscle to reach peak activation was the latissimus dorsi at 37.3% of the pull-up cycle with a magnitude of activation ranging from 117 ± 46% MVIC for the chin-up to 130 ± 53% MVIC for the rotational exercise using the Perfect·Pullup™ twisting handles. This muscle functioned to complete trunk elevation through reverse activation, which is made possible by pelvic stabilization from the erector spinae and external oblique. The latissimus dorsi also completed adduction and hyperextension of the shoulder to finish the concentric phase of the exercise cycle. Results from this study are consistent with the findings by Ricci et al. (33) whereby the most pronounced activity of the latissimus dorsi is at the completion of the concentric phase of the pull-up or chin-up cycle.
We identified an assortment of limitations in our study. As with all motion analysis, reflective markers are designed to measure skeletal kinematics; however, they are indirectly measuring joint angles via skin movement. Soft tissue artifact was inevitable because the only way to truly measure skeletal kinematics is through the use of needle penetration into bone. In addition, as with all EMG systems there is the potential for skin artifact and crosstalk. We minimized this by using standard EMG electrode placement as described by Cram and Kassman (10). The skin was wiped with alcohol, and shaved if needed, to clean the skin of oil and debris. Tape reinforced the EMG electrodes preventing the sensor from falling off the desired muscle motor point. Additionally, we used double-differential electrodes vs. single-differential electrodes which served to minimize the potential for crosstalk. To increase generalizability, future research should include subjects with varying age, activity level, BMI, and gender. Future research should examine joint forces to confirm the manufacturer's claim that joint contact forces are minimized because of the Perfect·Pullup's™ twisting handles allowing the arm to move in a natural motion to improve strength, balance, flexibility, and endurance, while reducing the risk of muscle strain and injury.
The pull-up or chin-up exercise can be used to train muscles used regularly in activities of daily living that involve pulling motions (shoulder extension combined with elbow flexion) of the upper extremity. Back, shoulder, arm, and trunk muscle activation patterns and elbow joint kinematic information are of interest to physical therapists and other fitness professionals when prescribing variations of the pull-up and chin-up exercise to their clients. Excessive emphasis placed on pressing movements in the upper extremity may increase the likelihood of shoulder complex trauma such as rotator cuff injury or strain. To prevent this, pulling movements should be incorporated in rehabilitation programs to achieve a balance between pressing and pulling performance. The 7 muscles of the back, shoulder, arm, and trunk examined in the present study during the pull-up and chin-up displayed high to very high muscle activation at a level that would be appropriate for strength training (1,4,28). Based upon normalized EMG activity alone, the rotational exercise using Perfect·Pullup™ twisting handgrips is not preferable to a conventional pull-up or chin-up when the goal is to produce muscle strengthening of back, shoulder, arm, and trunk muscles.
Funding for this project came from the Mayo Program in Physical Therapy, College of Medicine, Mayo Clinic, Rochester, MN, USA. The authors disclose they have no professional relationship with the company that manufactures the Perfect·Pullup™ device. The results of this study do not constitute endorsement of the Perfect·Pullup™ device by the authors or the National Strength and Conditioning Association. The authors wish to thank Mr. Mike Ilse for constructing the free-standing pull-up and chin-up apparatus.
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Keywords:© 2010 National Strength and Conditioning Association
muscle activation; motion analysis; kinematics