Differences in Muscle Activity During Cable Resistance Training Are Influenced by Variations in Handle Types

Abstract

Rendos, NK, Heredia Vargas, HM, Alipio, TC, Regis, RC, Romero, MA, and Signorile, JF. Differences in muscle activity during cable resistance training are influenced by variations in handle types. J Strength Cond Res 30(7): 2001–2009, 2016—There has been a recent resurgence in the use of cable machines for resistance training allowing movements that more effectively simulate daily activities and sports-specific movements. By necessity, these devices require a machine/human interface through some type of handle. Considerable data from material handling, industrial engineering, and exercise training studies indicate that handle qualities, especially size and shape, can significantly influence force production and muscular activity, particularly of the forearm muscles, which affect the critical link in activities that require object manipulation. The purpose for this study was to examine the influence of three different handle conditions: standard handle (StandH), ball handle with the cable between the index and middle fingers (BallIM), and ball handle with the cable between the middle and ring fingers (BallMR), on activity levels (rmsEMG) of the triceps brachii lateral and long heads (TriH_Lat, TriH_Long), brachioradialis (BR), flexor carpi radialis (FCR), extensor carpi ulnaris, and extensor digitorum (ED) during eight repetitions of standing triceps pushdown performed from 90° to 0° elbow flexion at 1.5 s per contractile stage. Handle order was randomized. No significant differences were seen for triceps or BR rmsEMG across handle conditions; however, relative patterns of activation did vary for the forearm muscles by handle condition, with more coordinated activation levels for the FCR and ED during the ball handle conditions. In addition, the rmsEMG for the ED was significantly higher during the BallIM than any other condition and during the BallMR than the StandH. These results indicate that the use of ball handles with the cable passing between different fingers can vary the utilization patterns of selected forearm muscles and may therefore be advantageous for coaches, personal trainers, therapists, or bodybuilders for targeted training or rehabilitation of these muscles.

Introduction

Handles are commonly used in industry and when performing activities of daily living to hold, move, and transport objects. According to Drury CG (⁹), the literature on handles can be classified into 3 major categories. The first classification is an examination of the type of force or torque produced by the hand on the handle; the second is an evaluation of the effect of the handle parameters; and the third classification is related to design parameters. Studies have shown that during the performance of certain tasks, the handle type, shape, weight, size, and even the type of force applied by the hand to a handle seem to significantly influence the muscle activity of the muscle group involved in the associated task (^4,5,16,22,25).

Design, shape, and weight of tool handles have significantly impacted torque production and muscle utilization patterns during use. Wang and Lin (²⁶) evaluated screwdrivers with different handle designs (square, triangular, circular, and pistol) and blade lengths and found that during maximal supination, the circular handle produced the highest peak torque (5.81 N·m), followed by the triangular (5.69 N·m), pistol (5.30 N·m), and square (3.86 N·m) handles. The electromyographic (EMG) responses in biceps brachii and flexor digitorum also revealed that the circular handle produced a lower rmsEMG when compared with the others. In a second study evaluating the impact of handles on tool use, Böhlemann et al. (⁵) analyzed three different electric hedge-clipper handles and found significantly different muscle activity levels because of the shape and weight of the handles.

Handle types can also influence perceived effort and the way a person grasps and uses tools. Hsia and Drury (¹⁸) performed analyzed optimal handle design comparing single or dual handles, angular deviations relative to the forearm, handle diameter, and handle curvature and found that subjectively reported efficiency differed significantly for each parameter. These results reflected those reported earlier for single and double-handed lifts (⁹), deviation angle (¹¹), handle diameter (^10,24), and shape (⁸). Furthermore, Winges et al. (²⁶) assessed grip force and muscle activity among handles with different compliancy levels and reported that the points of contact where the compliant surfaces were positioned affected the typical coupling between grip force and load force, and levels of muscle activity of the upper arm, forearm, and finger muscles. In addition, Cochran at al. (⁷) compared the grasp force and the perceived grasp force produced while using 5 different sizes of cylindrical handles and reported that for all handles, the grasp force showed a linear relationship with perceived percentage maximal voluntary contraction (MVC) until 80% was reached, at which time the relationship became curvilinear and subjects consistently overestimated the force they were applying. Grant et al. (¹⁶) studied three handle diameters and evaluated the effects of those handles on manual effort during a simulated industrial task. Electromyographic analyses revealed that the muscular effort increased significantly as the handle diameter and resistance increased. Normalized EMG values among handles were significantly different for all muscle groups (flexor pollicis longus, flexor digitorum superficialis, and extensor digitorum [ED]). Also, the smaller handle diameter generated the greatest grip strength compared with the other two handles. Finally, in a study evaluating grip force on cylindrical handle diameters, Kong and Lowe (²²) investigated how 6 cylindrical handle diameters (25, 30, 35, 40, 45, and 50 mm) affected force distribution, and electromyographic efficiency of finger flexor and extensor muscles. The results of the study showed that as the cylindrical handle diameter increased, the total finger forces decreased. In addition, the efficiency of the electrical activity was inversely related to handle diameter; however, the EMG values for finger flexors and extensors were not affected by the handle size.

Handle types can also influence muscle activity and force production during physical testing situation. For example, Amaral et al. (¹) compared grip strength using 3 different hand-held dynamometers with varying handle configurations. They reported significant differences among the dynamometers because of handle shape. In addition, Blackwell et al. (⁴) used four different handle positions (100, 130, 160, and 180 mm) to analyze the effect of grip span on isometric grip force and fatigue of the flexor digitorum superficialis muscle during 60–65% of MVC. They found that although the EMG values did not differ significantly among the four grip spans, the intermediate grip spans (130 and 160 mm) produced greater absolute forces than the small and large sizes.

Finally, variations in handle shape and size have been shown to influence exercise responses during training. Although we could find no studies examining the impact of these 2 variables as they relate to cable machine handles, bar diameter and shape have been examined during isometric exercise assessments. Fioranelli and Lee (¹³) compared 2 different bar diameters during a unilateral isometric bench press exercise. They found that although MVC did not vary by bar thickness, the thin bar produced greater neuromuscular activity for the pectoralis major and forearm muscles when compared with the thick bar. Drury et al. (¹²) evaluated an alternative to the standard round weightlifting bar and cable handle using a hexagonal handle, the tri-bar. They compared the traditional Olympic bar to the tri-bar using isometric hold times during bilateral body weight hang and a unilateral weighted bucket lift. Results were seen to vary by assessment with longer hang times for the bilateral body weight test using the tri-bar and longer bucket holding times using the traditional cylindrical handle.

Given the variations seen in performance and muscle utilization patterns due to handle design and the lack of information concerning handle design during cable-based resistance training, the purpose of this study was to analyze the differences in upper arm and forearm activity levels among 3 handle types during the triceps pushdown exercise using a commercially available cable machine. Clearly, the forearm musculature as it relates to the sport, daily activity and work environment represent the mechanical “motors” controlling movement of the wrist and hand critical to successful performance. Because the hand and wrist constitute the distal components of the kinetic chains used in tasks such as lifting, grasping, stabilizing, and transferring, targeting these muscles during gross movements is critical to improving performance and optimizing rehabilitation. Knowledge of forearm and upper arm muscle activity patterns using specific training interventions, such as modifications of handle shape and size, is critical to applying targeted interventions.

Methods

Experimental Approach to the Problem

Because the forearm muscles constitute the terminal link in the kinetic chain during many activities of daily living, sports activities, and material handling occupations, this study used a repeated-measures design incorporating three handle types on a selectorized cable machine. Participants were recruited from the student body of the university. After determination of appropriate loading for each handle type, participants performed a standard triceps pushdown exercise in a standing position using each of the 3 handless. The order of handle type use was randomized among subjects. Subjects performed 8 metronome-controlled repetitions for each condition with a 10-minute recovery provided between trials. Given the capacity of EMG analyses to quantify muscle use during exercise, muscular activity levels (rmsEMG) were used to measure differences among muscles for each machine and differences among machines by muscle group. The study design is presented in Figure 1.

Figure 1.: Experimental protocol.

Subjects

Participants were healthy college-aged men and women (19–35 years of age) with at least 2 years recreational resistance-training experience having no history of neuromuscular disease or injuries that might have affected their performances during testing. Participants reported a minimum of 2 training days per week. All procedures were approved by the Committee for the Use and Protection of Human Subjects and participants provided written consent. Participants' characteristics are provided in Table 1.

Table 1.: Participant characteristics (mean ± SD).*†

Procedures

Participants attended 2 testing sessions. During the first session, 8 repetition maximum loads were established for the standard triceps pushdown exercise using each of 3 different handles attached to a cable machine (Bravo Pro; Cybex Corp., Medway, MA, USA) (Figure 2A). The 3 handle conditions were standard handle (StandH; Figure 2B), ball handle with the cable extended between the index and middle fingers (BallIM, Figure 2C), and ball handle with the cable extended between the middle and ring fingers (BallMR, Figure 2D). To reduce any learning effect, subjects were provided familiarization training with each handle. In addition, to assure similar testing environments across all exercises, subjects maintained the glenohumeral joint at zero degrees of flexion and the exercise was performed starting with the elbow at 90° flexion and extending to the subject's full elbow extension (Figure 3). Participants were instructed to keep the wrist in a neutral position throughout each exercise. When the tester saw deviations from these parameters, the trial was stopped and corrections were made.

Figure 2.: Illustrations of the ball handle and standard handle (A), standard handle condition (B), index-middle fingers ball handle condition (C), and middle-ring fingers ball handle condition (D).

Figure 3.: Illustration of the starting position for the triceps extension exercise.

Participants returned for a second day of testing within 48 hours. After a short warm-up, they performed 8 repetitions of the triceps pushdown exercise in a standing position using each of the 3 handle types. The order of handle types used was randomized among subjects. Subjects performed the repetitions to a metronome set at 1.5 s per contractile stage (concentric, eccentric). Ten-minute recovery periods were provided between trials.

Electromyography

Electromyography was used to quantify neuromuscular activity in the 6 muscles of interest, the triceps brachii lateral head (TriH_LAT), triceps brachii long head (TriH_LONG), brachioradialis (BR), flexor carpi radialis (FCR), extensor carpi ulnaris (ECU), and ED. A bipolar surface configuration was used to maximize the reception area while controlling the potential for crosstalk among the muscles examined (³). To assure accurate electrode placement, the motor point locations of each muscle were determined using a Grass S88 stimulator (Grass Medical Instruments, Quincy, MA, USA) delivering a series of 5-millisecond pulses at a rate of 5 pulses per second at a progressively reduced voltage (starting between 40 and 60 V) until only 1 point on each muscle elicited a response. This was considered the motor point for the muscle. The skin surface proximal to each motor point was shaved, lightly abraded, and cleaned with alcohol to remove dead surface tissues and oils that might reduce the fidelity of the signal. Disposable Ag/AgCl pregelled disk surface electrode pairs (Noraxon USA, Scottsdale, AZ, USA) were positioned at each area parallel with the underlying muscle fibers, as determined by the pennation of the muscle. Electromyographic data during all triceps pushdown exercises were collected from the participant's dominant side.

Raw EMG signals were recorded using a wireless EMG telemetry system (Noraxon USA) with an input impedance of 2 MV and a common mode rejection ratio of 100 db. The gain was set at 2,000 with band pass filtering set between 3 and 500 Hz. Signals were sampled at a speed of 1,500 Hz, digitized using a 16-bit A/D converter (Noraxon USA), and stored on a personal computer. Recorded EMG signals from each muscle were analyzed using a custom software program (Labview Software, National Instruments, Austin, TX, USA) written to quantify the rmsEMG. The rmsEMG was used as a measure of average muscle activation for each muscle during all handle conditions.

Statistical Analyses

Three separate 6-factor (muscle) repeated-measures analysis of variance (ANOVA) were used to evaluate comparative rmsEMG levels among muscles for each of the handle conditions, whereas 6 separate 3-factor (handle condition) repeated-measures ANOVA were used to evaluate rmsEMG levels for each muscle under different handle conditions. Statistical significance was set a priori at p ≤ 0.05. All statistical procedures were performed using the SPSS statistical package (version 22.0; SPSS, Inc., Chicago, IL, USA). When a significant main effect or interaction was detected, the least significant difference post hoc test was used to determine the sources of the differences.

Results

Results Among Muscles Within Handle Types

The repeated-measures ANOVA for the StandH revealed a significant difference across muscle groups (F = 18.432; p < 0.0001; η = 0.445). Figure 4A provides the rmsEMG values for each muscle (mean ± SE), whereas Table 2 provides pairwise comparisons. As can be seen in Figure 4A, the activity levels for the TriH_LAT and TriH_LONG were not significantly different; however, pairwise comparisons revealed significantly higher means for these muscles compared with all others. Moreover, the electrical activities for the BR and FCR were significantly different from all other muscles. Finally, the rmsEMG values for the ECU and ED did not differ significantly.

Figure 4.: The rmsEMG values for each muscle for the standard handle (A), index-middle fingers ball handle (B), and middle-ring fingers ball handle cable positions (C). Muscles with the same letters are not significantly different from each other (p ≤ 0.05). BR = brachioradialis; FCR = flexor carpi radialis; ECU = extensor carpi ulnaris; ED = extensor digitorum.

Table 2.: Differences in muscle activity (rmsEMG) among muscles for the standard cable handle.

A significant difference by muscle group was also detected for the BallIM condition (F = 22.447; p < 0.0001; η = 0.494). The rmsEMG values for individual muscles (mean ± SE) during this condition are show in Figure 4B, whereas Table 3 provides pairwise comparisons. Although the activity levels for the TriH_LAT and TriH_LONG were not significantly different, pairwise comparisons revealed significantly higher mean rmsEMG values for these muscles compared with all others. Furthermore, the rmsEMG values for the FCR and ED did not differ significantly, but were significantly different from all other muscles tested.

Table 3.: Differences in muscle activity (rmsEMG) among muscles for the index-middle finger cable handle.

For the BallMR condition, a significant main effect was again detected by muscle (F = 19.626; p < 0.0001; η = 0.460). Mean ± SE and pairwise comparisons for this condition are seen in Figure 4C and Table 4, respectively. Once again the activity levels for the TriH_LAT and TriH_LONG were not significantly different, but the analyses revealed significantly higher mean values for the TriH_LAT and TriH_LONG compared with all other muscles. Moreover, the electrical activities for the BR were significantly different from all forearm muscles. In addition, the rmsEMG values for the FCR and ED did not differ significantly nor did the rmsEMG values for the ECU and ED.

Table 4.: Differences in muscle activity (rmsEMG) among muscles for the middle-ring finger cable handle.

Results by Exercise

The mean ± SE for the rmsEMG values of individual muscles during the three handle conditions is provided in Figure 5A–F. In examining the differences among handles for different muscle groups, no significant differences were detected for the TriH_LAT, TriH_LONG, BR, FCR, or ECU; however, a significant main effect was detected for the ED (F = 19.719; p < 0.0001; η = 0.462) (Figure 5F). For this muscle, rmsEMG values were significantly higher during the BallIM condition compared with the StanH (mean_diff ± SE = 61.00 ± 11.28 μV; 95% CI (37.67–84.33 μV); p < 0.0001) and BallMR conditions (mean_diff ± SE = 34.14 ± 9.37 μV; 95% CI (14.77–53.51 μV); p < 0.001). The BallMR exercise also presented a significantly higher mean rmsEMG for the ED than the StanH condition (mean_diff ± SE = 26.86 ± 8.34 μV; 95% CI (9.62–44.11 μV); p < 0.004).

Figure 5.: The rmsEMG values for each handle type for the triceps brachii lateral head (A), triceps brachii long head (B), brachioradialis (C), flexor carpi radialis (D), extensor carpi ulnaris (E), and extensor digitorum (F). *Significantly greater than the standard handle condition. **Significantly greater than the standard handle and index-middle finger ball conditions (p ≤ 0.05).

Discussion

The results among muscles for each handle type were consistent with the TriH_LAT and TriH_LONG producing the highest rmsEMG among all muscles and the BR showing the lowest activity levels. The activity patterns for the forearm muscles, however, varied considerably across handles. For the StanH, FCR activity was significantly higher than the ECU and ED, which did not differ from each other. In contrast, for BallIM, the activities of the FCR and ED did not differ significantly, but were both higher than the ECU. Finally, for the BallMR, the rmsEMG for the FCR and ED did not differ nor did the rmsEMG values for the ECU and ED.

In examining differences among handles for each muscle groups, no significant differences were detected for any muscle with the exception of the ED where rmsEMG values were significantly higher during the BallIM than the StanH and BallMR conditions. The BallMR exercise also produced significantly higher activity than the StanH.

The triceps pushdown is a traditional exercise used during resistance training to target the triceps surae group (^15,17). The TriH_LAT originates halfway down the posterior and lateral humerus and lateral intermuscular septum, whereas the TriH_LONG originates at the infraglenoid tubercle of the scapula. Both insert through a common tendon at the posterior olecranon process of ulna (²¹). For the purpose of the triceps extension exercise, they share the common function of forearm extension through the humeroulnar hinge and the humeroradial spheroidal joints. Given the common function of these muscles and the limited degrees of freedom of the elbow joint, the greater activities of these muscles relative to the others tested and their similarities in rmsEMG across handle conditions was expected.

The low level of activity for the BR compared with the other muscles tested across all handle conditions is consistent with its structure and function. Its origin is on the proximal two-thirds of the lateral supracondylar ridge of the shaft of the humerus and its insertion is on the lateral base of the styloid process of the radius (²¹). It primary function, therefore, is flexion of the elbow, but it also aids in pronation and supination when resistance is applied to forearm (²¹). Therefore, it serves as an antagonist muscle during the triceps pushdown exercise but may also work in stabilizing forearm position.

The ordered levels of electrical activity ranging from highest using during the BallIM to the lowest using the standard handle for all forearm muscles, which reached statistical significance for the ED, are reflective of the hypothesis offered by many strength coaches that thicker lifting bars will more effectively activate forearm muscles throughout selected lifts such as inclined press, chest press, rows, biceps curl variations, and standing latissimus dorsi exercises (⁶). However, Fioranelli and Lee (¹³) reported greater electrical activity in the forearm muscles during the performance of a unilateral isometric bench press using a standard (28 mm) rather than “fat” bar (51 mm). The difference between our results and theirs may have been due to a number of factors, the most obvious of which is the nature of the exercise performed, the dictated vectors of force application, especially given the variation in handles in this study, the different loading characteristics, the nature of the contractions, and the necessity to grasp the handles rather than simply push against a bar. The higher electrical activities of the forearm muscles during the ball conditions reflect the findings by Kong and Lowe (²²) that indicated a reduction in the efficiency of electrical activity with increases in handle diameter.

The fact that the ball handles progressively reduce the ability of the exerciser to make a fist for the StanH, BallIM, and BallMR, respectively, as the cable passes through the spaces between the index and middle compared with the middle and ring fingers may also have increased activity levels of the FCR and ED as the fingers are forced into abduction about the circumference of the ball accounting for the lack of differences between these muscles during the BallIM and BallMR conditions.

The angles at which forces are exerted at the hand/handle interface are also important factors in dictating forearm muscle activation. Böhlemann et al. (⁵) demonstrated that both electrical activity of selected forearm muscles and perceived effort were affected by handle angle when using different hedge-clipper models. In this study, the angle between the cable and shaft of the forearm ranged from approximately 30°–20° when using the ball handles compared with a more efficient range of approximately 20°–15° using the standard handle.

Only 2 studies, to our knowledge, have compared the use of a modified handles to standard handles commonly used in cable training. The first evaluated the Maxagrip handle (Barton Innovations, Waynesfield, OH, USA) (²) and the second evaluated a hexagonal handle called the tri-bar (⁸) as they related to standard handles. Direct comparisons to this study, however, are not possible since neither study examined muscle activity levels during testing. Variables assessed were isometric strength in the former study and endurance in the later, and cable systems were not used during either investigation.

This study had a number of limitations. First, subjects' training histories, especially as they relate to the use of cable systems, were not established. Second, the study could be repeated with a larger number of subjects; however, given the effect sizes, differences in results are doubtful. Third, a training study and an acute study with a prolonged familiarization period are both warranted because participants in the study reported a greater perceived ability to target forearm muscles after 2–3 weeks of regular use of the ball handles. Fourth, using dedicated transducers, the forces among fingers and across the palmar surface of the hand should be measured to better explain our results. Fifth, time of day, nutritional status, and hydration levels were not evaluated. And finally, these handles should be examined across other exercises to determine the feasibility of their use.

Practical Applications

The use of EMG in this study allowed us to quantify muscular activities during each of the handle conditions rather that depending on other less exacting methods such as perceived exertion. This methodology allows us to conclude that given the capacity, albeit somewhat limited, of the ball handles to target specific forearm muscles while allowing similar activity levels for the triceps, they may provide a feasible alternative to standard handles for physical therapists, athletic trainers, and strength and conditioning professionals who wish to target muscles specific to rehabilitation, prevention, or performance. For example, the greater electrical activity levels for the ball handles versus standard handle for all forearm muscles, which reached statistical significance for the ED, are important given their relationship to handgrip performance. Handgrip strength has been shown to be associated with independence and disability in older and middle-aged individuals (²⁰). It is also a critical physical component dictating success in a variety of sports such as rock climbing (¹⁵), tennis (²³), wrestling (¹⁴), and job-related performance such as object manipulation (¹⁹). In addition, competitors such as bodybuilders or form and fitness competitors may find these handles helpful in targeting specific muscles of the forearm.