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European Journal of Sport Science logoLink to European Journal of Sport Science
. 2024 Dec 23;25(1):e12243. doi: 10.1002/ejsc.12243

Eight‐week lat pull‐down resistance training with joint instability leads to superior pull‐up endurance performance and reduced antagonist coactivation in recreationally active male college students

Qian Li 1, Jiaqi Yan 1, Minjie Qiao 2, Jiuqing Quan 1, Yiqing Chen 1, Mingxin Gong 1, Wenxin Niu 3, Lejun Wang 1,✉
PMCID: PMC11667758  PMID: 39716392

Abstract

This study aimed to investigate the effects of an 8‐week lat pull‐down resistance training program with joint instability on pull‐up performance in male college students. Thirty‐four healthy recreationally active male college students were randomly assigned to either the joint instability resistance training (IRT) or traditional resistance training (TRT) group. Participants of the TRT and IRT groups performed lat pull‐down training on stable and joint instability conditions for 8 weeks, respectively. Pull‐up endurance (number of repetitions), anthropometry, lat pull‐down maximal voluntary isometric contraction (MVIC) peak force, and movement stability of performing unstable lat pull‐down were tested before and after the 8‐week training. Surface electromyography of biceps brachii (BB), triceps brachii (TB), brachioradialis (BR), anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), pectoralis major (PM), and latissimus dorsi (LD) muscles were recorded during the pull‐up endurance test. The level of significance is set at p ≤ 0.05. The results demonstrated that the pull‐up endurance and lat pull‐down MVIC peak force of both IRT and TRT groups were significantly enhanced after 8‐week training compared to the pre‐training test. Notably, the number of pull‐up repetitions of the IRT group was 45.5% higher than the TRT group. These findings suggest that lat pull‐down training performed with joint instability may lead to greater improvements in pull‐up endurance compared to the stable condition, possibly attributed to enhanced muscle contraction efficiency as indicated by decreased antagonist coactivation activity.

Keywords: biomechanics, coaching, endurance, strength, training

Highlights

  • It is the first study to explore the effects of resistance training with joint instability on improving pull‐up endurance performance.

  • 8 weeks of lat pull‐down resistance training performed on stable and unstable conditions can both enhance pull‐up endurance and lat pull‐down strength for recreationally active young individuals.

  • The lat pull‐down resistance training performed on the unstable condition was superior in pull‐up endurance improvement than stable conditions.

  • The superior training gains of joint instability resistance training may be attributed to enhanced muscle contraction efficiency as indicated by decreased antagonist coactivation.

1. INTRODUCTION

The pull‐up is a resistance exercise widely used in measuring the strength and endurance of the elbow and shoulder girdle, which has been generally scored by counting the maximum number of valid repetitions (Beckham et al., 2018; Sánchez‐Moreno et al., 2020; Thomas et al., 2018). The ability to perform pull‐ups has been shown to significantly correlate with the completion of motor tasks such as climbing, pushing, pulling, lifting, and chopping (Vigouroux et al., 2019; Williford et al., 1999). It is very important for certain occupational settings such as law enforcement, military, and firefighting (Lester et al., 2014; Stone et al., 2020). Moreover, pull‐up has been accepted as a physical fitness test parameter in many areas (Sedliak et al., 2021; Vaz et al., 2021). However, pull‐up may be a challenging exercise as it demands not only stronger muscle strength to lift one’s own body weight but also skills of multi‐joint coordination (Flanagan et al., 2003; Sánchez‐Moreno et al., 2020). For this point, exploring effective interventions to promote pull‐up endurance performance should be encouraged.

Resistance training is an effective tool for improving muscle strength, endurance, and exercise performance by stimulating muscle hypertrophy and neuromuscular adaptations (Grgic et al., 2020; Schoenfeld et al., 2015). In recent decades, performing resistance training with instability challenges, which primarily affect posture and joint stability, has become increasingly popular in both the general fitness world and specialized strength training for competitive sports (Moosaei Saein et al., 2024; Sanchez‐Sanchez et al., 2022). Instability resistance training employs unstable conditions to enhance exercise performance (Panza et al., 2014). This approach often involves performing exercises on unstable surfaces such as balls (Elfateh, 2016) and wobble boards (Clark & Burden, 2005) or using unstable devices and dynamic loads such as elastic bands (Dunnick et al., 2015), water‐filled tubes (Glass & Albert, 2018), and suspended chains (Aguilera‐Castells et al., 2020). It has been demonstrated that instability resistance training can provide a more intense stimulus for the neuromuscular system (Behm & Anderson, 2006) and ensure high muscle activation with less force or torque on joints under moderate instability (Behm & Colado Sanchez, 2013). Research suggest that instability resistance training can bring superior training gains than traditional resistance training in strength (Sparkes & Behm, 2010), endurance (Lima et al., 2018), explosive force (Abuwarda et al., 2024), and countermovement jump (Kibele et al., 2014). However, instability may also impair force, power, velocity, and range of motion due to stiffness of joints (Behm & Anderson, 2006; Behm et al., 2010). As joint stability decreases, muscles may transition from a mobilizing to a stabilizing function by establishing active muscular constraints to minimize the degrees of freedom in joints (Anderson K. G. & Behm, 2004). Therefore, further research is necessary to confirm the effects of resistance training with joint instability on muscle strength and endurance performance.

On the other hand, considering that most students in China cannot even complete one standard pull‐up, and over half of the college students fail to score effectively in pull‐up tests (He & Shi, 2019), a more suitable resistance training method to simulate pull‐up resistance is required. One calisthenics exercise that is analogous to the pull‐up exercise is lat pull‐down (Johnson et al., 2009). The lat pull‐down is a weight‐adjusted cable exercise that closely mimics the vertical pulling‐down motion of the pull‐up. Therefore, the lat pull‐down has been suggested as an alternative for adding volume and building muscle and strength for recreational beginners who have difficulty in completing several pull‐ups. Moreover, the pull‐up endurance has been adopted to predict the 1RM of lat pull‐down, indicating the close relationship between the two exercises. The similarities between the two exercises are especially comparable in situations where the orientation of the forearms and the width of the grip are more equivalent during the exercise (Lusk et al., 2010; Signorile et al., 2002). Hence, lat pull‐down exercise would be a suitable method for pull‐up resistance training. As addressed by some studies on unstable bench press training (Costello, 2022; Lawrence et al., 2021), it is possible to use elastic bands to induce an unstable load and create joint instability in unstable lat pull‐down resistance training. However, as the issue has not been widely concerned, no previous research has discussed the differences between unstable and stable lat pull‐down resistance training in improving pull‐up performance.

Surface electromyography (sEMG) is a noninvasive method used to measure the electrical activity of muscles during contraction. It provides powerful tools to evaluate muscle activity and neuromuscular control strategy (Massó et al., 2010). Specifically, the amplitude of EMG has been proved to have a close relationship with the number of motor unit recruitment and muscle force output and thus may give insights for the assessment of training‐related neuromuscular adaptations (Cavalcanti Garcia & Vieira, 2010).

Based on the above analysis, this study aimed to compare the effects of lat pull‐down resistance training under stable versus unstable conditions on pull‐up endurance and the EMG activity of agonist and antagonist muscles. The findings are intended to provide evidence for optimizing training protocols to enhance pull‐up performance. Referencing previous studies (Behm & Anderson, 2006; Behm & Colado Sanchez, 2013; Costello, 2022; Lima et al., 2018), we hypothesize that the lat pull‐down training with joint instability would provide greater training improvements than stable training.

2. METHODS

2.1. Experimental approach to the problem

As shown in Figure 1, the experimental approach involved four sessions: familiarization, pre‐training test, training interventions, and post‐training test. To specialize in the lat pull‐down exercise, each subject was first required to receive a 1‐week familiarization training. During the familiarization session, a brief training introduction was reported to participants about the training protocol and testing requirements. All participants received both stable and unstable lat pull‐down practice until they were skilled at the exercises. Each participant should perform a lat pull‐down resistance training program for 8 weeks. Pre‐training and post‐training measures were conducted before and after the training intervention.

FIGURE 1.

FIGURE 1

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Experimental approach to the problem.

The test procedure consisted of 2 distinct phases separated by a 72 h interval. During the first phase, participants underwent anthropometric measurements and assessed their one‐repetition maximum (1RM) in the lat pull‐down exercise. In the second phase, the evaluation included the pull‐up endurance, lat pull‐down maximal voluntary isometric contraction (MVIC) peak force, and movement stability during unstable lat pull‐downs. EMG signals were recorded throughout the pull‐up endurance test. To prevent potential injuries, participants performed a dynamic warm‐up that included 3 min of jogging, 5 min of upper‐body stretching, and 5 lat pull‐down repetitions at 30% of their 1RM workload. A 3 to 5 min break was provided during each test session to alleviate fatigue effects. Participants were also instructed to refrain from physical exercises and to avoid food, caffeine, and alcohol consumption for 48 h before the measurements.

2.2. Subjects

Referring to relevant previous research (Unhjem et al., 2016), the minimum sample size of 24 (12 per group) was determined to be sufficient utilizing repeated measurements analysis of variance (ANOVA) with the G × Power 3.1 software (Heinrich Heine, Dusseldorf, Germany). The effect size (f2) was set at 0.30 achieving a power of 0.80 at a significance level of 0.05 (Cohen, 1992). Considering potential dropouts, an additional 10 more participants were recruited and the total number of participants enrolled in the training program was 34. Participants were randomly assigned to either the joint instability resistance training (IRT) or traditional resistance training (TRT) group.

Participants were included if they met the following criteria: (1) male college students; (2) recreationally active, engaging in moderate‐intensity physical activity 2–3 times a week for at least 6 months; (3) maintained a body mass index (BMI) within the normal range (18.5–24 kg/m2); (4) right‐handed; and (5) provided written informed consent.

Participants were excluded if they (1) failed to complete one pull‐up; (2) had a history of upper limb or back injuries or surgeries within the past year; (3) suffered from neuromuscular disorders; or (4) participated in systematic upper limb and back strength training, such as rock climbing or rowing, within the past 6 months.

2.3. Training program

The 2 groups (IRT vs. TRT) undertook a regimen of lat pull‐down exercises 3 times weekly over an 8‐week duration, comprising 4 sets per session with 12 repetitions per set. Participants in the TRT group performed exercises on the traditional lat pull‐down strength trainer (Dr. Iron, Dr. Iron Fitness Equipment Company, China). The IRT group utilized a modified setup wherein two elastic bands (Decathlon, France) were affixed to the ends of the barbell inducing an unstable load. Participants in the IRT group grasped the elastic bands positioned 10 cm from the barbell, whereas the seat height was lowered by 10 cm as illustrated in Figure 2. To produce proper movement instability, 3 capacities of elastic bands were used to fit different workloads (type 1–3 elastic bands for the workloads of 0–30, 30–50, and 50–70 kg).

FIGURE 2.

FIGURE 2

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Figure depicts the traditional lat pull‐down resistance training machine (left) and unstable lat pull‐down resistance training machine (right).

Before each training session, participants were asked to complete the 10 min warm‐up routine as previously described. During the lat pull‐down exercises, participants sat on the lat pull‐down strength trainer (Dr. Iron, Dr. Iron Fitness Equipment Company, China). They were instructed to adjust the seat height to initiate the lift with fully extended arms and quadriceps supported. A pronated grip, 10–20 cm wider than shoulder width, was adopted, and the horizontal bar was pulled down in front of the head until reaching beneath the chin. Maintaining a neutral head position was emphasized to prevent chin elevation throughout the full range of motion (Johnon et al., 2009). Each repetition of the lat pull‐down took 6 s to complete, involving a rapid pull‐down phase from the first to the second second, a sustained contraction phase in the third second, and a slow return phase from the fourth to the sixth second. A 3‐min rest interval separated each set. In accordance with previous literature recommending moderate training volumes ranging from 60% to 80% of 1RM for optimal strength gains (González‐Badillo et al., 2005, 2006; Sánchez‐Moreno et al., 2020), the training load was progressively increased by 5% of 1RM every 2 weeks, commencing at 65% of 1RM in the initial 2 weeks and concluding at 80% of 1RM in the final 2 weeks of the intervention period.

2.4. Procedures

Anthropometry. Height and weight were measured using a portable stadiometer and an electronic scale before and after 8 weeks of resistance training. Body mass index (BMI) was then calculated using the following formula: BMI = weight (kg)/height (m)2. To measure the sum of the muscle and subcutaneous fat in the upper arm, participants received the midupper arm conference (MUAC) measurement by laying a flexible nonelastic band at the midpoint between the olecranon process and the acromion (Allen, 2013). Measurement was conducted before participants’ warm‐up and the value of the measurement was recorded as the test result.

Pull‐up Endurance. Before and after the training, participants completed pull‐ups until unable to lift their bodies to the standard horizontal bar using a pronated grip positioned 10–20 cm wider than shoulder width (Lombardi, 1989). After reaching the chin level with the bar, participants slowly returned to the starting position marking a successful pull‐up (Snarr et al., 2017). The researchers verbally monitored the consistency of the pace and rhythm of pull‐ups and recorded the total number of repetitions performed.

Electromyography (EMG). In accordance with previously published reports (Behm et al., 2002, 2005) and SENIAM (http://seniam.org/) recommendations, EMG electrodes were placed collar to collar (2 cm) on the midbellies of the biceps brachii (BB), triceps brachii (TB), brachioradialis (BR), anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), pectoralis major (PM), and latissimus dorsi (LD) on the right side of the body. Skin preparation for the electrodes included shaving and light abrading followed by alcohol swabbing. Electromyography was collected using a wireless EMG system (BTS FREEEMG 1000, BTS, Garbagnate Milanese MI, Italy) at a sample rate of 1000 Hz. Before testing pull‐up EMG, muscles’ MVC EMG were measured according to The ABC of EMG for standardization (Konrad, 2006). A fourth‐order Butterworth filter was used to perform band‐pass filtering on the collected surface EMG, with a filtering frequency of 5–500 Hz and a filtering mode of zero‐phase offset filtering. The full‐wave rectification was performed on the surface EMG recorded from the pull‐up test, based on which the root mean squared (RMS) EMG was calculated by moving with the width of the time window of 50 ms, in order to obtain the envelope of the surface EMG. For the EMG activity measures, the RMS EMG of the whole pull‐up period was normalized to MVC EMG to reflect the excitation level (Vigotsky et al., 2017) of the agonist and antagonist muscles. Moreover, antagonist muscle coactivation ratios of TB/(BB + BR), AD/PD, and MD/PD were also calculated referenced to relevant previous research (Latash, 2018; Torres et al., 2017).

One Repetition Maximum Lat Pull Down Test. Each participant completed the lat pull‐down 1RM test to conform the training weight before the 8‐week training program. The 1RM assessment adhered to the prescribed protocols outlined by the American College of Sports Medicine (2017). Weight increments were applied progressively until participants reached their maximal lifting capacity for the exercise. Initially, participants engaged in a 5 min general warm‐up, during which the essentials and safety precautions of the lat pull‐down were elucidated. This was followed by a warm‐up set comprising 8 repetitions at 30% of their estimated 1RM aimed at familiarizing participants with the movement pattern. For the first trial, participants performed repetitions at approximately 50%–70% of their estimated 1RM, with a rest period of 1–3 min following the warm‐up. Following a 3‐min rest interval, the load was increased by 5%–10% of the initial weight. If successful, the weight was incrementally increased until participants could perform only one repetition. Conversely, if unsuccessful, the weight was reduced by 2.5%–5% and another attempt was made. Participants completed the test in four trials, with a rest period between each trial of approximately 3 min, and the final highest load achieved was recorded as the 1RM load.

Lat Pull‐down Maximal Voluntary Isometric Contraction Force. At the outset, participants were securely positioned. Participants held the bar with their hands in an orthogonal position, with a distance of 1.2 times the shoulder width between the 2 hands, and the height of the seat was adjusted so that participants’ shoulder flexion and elbow flexion angles were kept at 90° and 120°, respectively. With this setup, participants were instructed to execute the lat pull‐down movement as swiftly and forcefully as possible, aiming to complete the action within a 5 s timeframe. Two trials were conducted, each separated by a 3 s rest interval. Verbal encouragement was provided throughout the trials to optimize force generation. At the same time, a pull dynamometer (Kinvent Kforce Link, model: K‐Pull; French) connected to the bar monitored participants’ maximal force output at a default sampling rate of 125 Hz. The maximal force measured between the two trials by the application software accompanying the device was taken as the result.

Movement stability of performing unstable lat pull‐down. Following the initial warm‐up, participants were instructed to perform 5 unstable lat pull‐down repetitions using a load equivalent to 30% of their 1RM. The pull‐down tempo matched the training tempo. An inertial motion capture system (STT‐isen, model: IWS, Spanish) was utilized, with a three‐dimensional inertial sensor affixed to the leftmost end of the barbell bar to capture and measure the acceleration. Data acquisition occurred at a sampling frequency of 400 Hz, recording the three‐axis acceleration data (X, Y, and Z axes) corresponding to the frontal, sagittal, and vertical planes of the participants, respectively.

Acceleration signals during rest periods were excluded and signals for each lat pull‐down were captured. Following the methodology of a previous study (Wang et al., 2022), a fourth‐order Butterworth filter was applied to band‐pass filter the acceleration data along the X, Y, and Z axes within the range of 0.8–200 Hz. Subsequently, acceleration data along these axes recorded during the unstable lat pull‐down test were subjected to full‐wave rectification. The average amplitude of acceleration along each axis was then calculated, serving as an index to assess the stability of the unstable lat pull‐down maneuver.

2.5. Statistical analyses

Statistical analyses were performed using SPSS version 22.0 Windows (SPSS, Inc. Chicago, IL, United States). All preintervention and postintervention data were expressed as mean ± standard deviation (SD). The normality and homogeneity of variances within data were confirmed with the Kolmogorov–Smirnov and Levene tests, respectively. Comparisons of anthropometry, pull‐up endurance and lat pull‐down MVIC were analyzed by 2‐way ANOVA [2 training groups (IRT vs. TRT) × 2 times (pre‐training vs. post‐training)] with repeated measures. 3‐way ANOVA was adopted to analyze the differences in the movement stability of performing unstable lat pull‐down (2 training groups × 2 times × 3 planes) and EMG activity (2 training groups × 2 times × 5 agonist/3 antagonist muscles). Due to the abnormal distribution of antagonist muscle coactivation ratios, nonparametric tests were applied. The Wilcoxon signed‐rank test compared pre‐training and post‐training differences within each group, whereas the Mann–Whitney U test was used to assess differences between the two groups during the pre‐test and post‐test phases. The level of significance was set at p ≤ 0.05. Effect sizes (ESs) were calculated and reported. Cohen’s d values equal to or greater than 0.2, 0.5, and 0.8 were used to determine whether the effect sizes (magnitude of change) were small, medium, or large.

3. RESULTS

3.1. Pull‐up endurance (number of repetitions)

Figure 3 presents the results of pull endurance tests. After training, pull‐up repetitions increased from 2.18 ± 1.42 and 2.18 ± 1.51 before training to 8.47 ± 3.54 and 5.82 ± 3.36 after training for IRT and TRT groups, respectively. A training group × time interaction (F = 8.61, p < 0.01, and ES = 0.21) was observed. After the training, the number of pull‐ups participants completed showed a 228.38% increase compared to the pretesting period and the IRT group performed significantly more pull‐up repetitions (45.5%) compared with the TRT group.

FIGURE 3.

FIGURE 3

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Figure illustrates pre‐training to post‐training mean and SD of the maximal number of pull‐up repetitions changes with TRT and IRT trained groups. *Detail the significant pre‐training to post‐training increases in the number of pull‐up repetitions.

3.2. Anthropometry

The anthropometric results for subjects in IRT and TRT groups before and after training are shown in Table 1. No significant main effects of training time and group as well as the interaction effect between time and group on anthropometry results (including height, weight, BMI, and MUAC) were found. After 8 weeks of training, subjects did not show significant changes in anthropometry results compared to pre‐training.

TABLE 1.

Anthropometry results of participants.

IRT (Age: 19.00 ± 6.31) TRT (Age: 18.65 ± 0.79)
Pre‐testing Post‐testing Pre‐testing Post‐testing
Height (cm) 175.41 ± 4.87 175.21 ± 5.16 173.64 ± 7.41 173.59 ± 7.24
Weight (kg) 65.17 ± 8.74 63.58 ± 7.64 62.15 ± 7.78 61.06 ± 8.26
BMI (kg/m2) 21.21 ± 2.07 20.70 ± 2.08 20.57 ± 2.25 20.25 ± 2.26
MUAC (cm) 26.33 ± 2.49 26.02 ± 2.45 25.79 ± 2.64 25.52 ± 2.57
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Note: MUAC denotes the midupper arm circumference. No significant difference was found.

3.3. Lat pull‐down maximal voluntary isometric contraction peak force

As shown in Figure 4, a significant main effect of time (F = 96.59, p < 0.001, and ES = 0.75) was detected for lat pull‐down MVIC peak force, indicating that strength increased by 24.9% from pre‐training to post‐training, whereby the IRT group increased their lat pull‐down MVIC peak force by 24.1% compared with a 27.9% increase in the TRT group. In addition, the main effect of the training group factor and the interaction between the training group and time were not observed, indicating no significant differences between the pre‐training or post‐training period.

FIGURE 4.

FIGURE 4

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Figure illustrates mean and SD of the lat pull‐down MVIC peak force changes pre‐training to post‐training for the TRT and IRT groups. *Indicate that both two groups motivated greater power than 8 weeks ago.

3.4. Movement stability of performing unstable lat pull‐down

Table 2 presents the integrated amplitude of shaking acceleration in both groups before and after training. Two interactions were detected: one between the training groups and planes (F = 4.46, p = 0.02, and ES = 0.12) and the other between training time and groups (F = 9.33, p < 0.01, and ES = 0.23).

TABLE 2.

Integrated amplitude of shaking acceleration.

IRT TRT
Pre‐testing Post‐testing p Pre‐testing Post‐testing p
Frontal plane 51.2 ± 13.1 45.3 ± 8.8 0.05* 46.1 ± 11.4 53.1 ± 11.3 0.03*
Sagittal plane 91.5 ± 88.8 80.3 ± 14.7 88.8 ± 14.8 96.5 ± 17.2
Vertical plane 96.8 ± 21.4 89.2 ± 19.0 86.3 ± 16.3 99.6 ± 17.5
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Note: * Indicate significant pre‐training to post‐training changes.

The training group × plane interaction demonstrates that shaking acceleration in the IRT group varied considerably across all three planes (frontal vs. sagittal: p < 0.01; frontal vs. vertical: p < 0.01; and sagittal vs. vertical: p < 0.01). In contrast, the TRT group exhibited substantial differences between the frontal and sagittal planes (p < 0.01) as well as the frontal and vertical planes (p < 0.01), whereas the difference between the sagittal and vertical planes was not pronounced. Regarding the interaction between training times and groups, a simple effects analysis showed that shaking acceleration significantly increased (p = 0.03) in the TRT group, whereas it decreased significantly (p = 0.05) in the IRT group after the 8‐week training period. In the post‐test phase, the amplitude of shaking acceleration in the IRT group was significantly 13.8% lower (p = 0.03) than that of the TRT group.

3.5. EMG activity

3.5.1. Agonist muscle activation

The EMG RMS amplitudes of agonist muscles of the subjects during the pull‐up endurance test before and after training are shown in Table 3. The 3‐way ANOVA result indicated a significant main effect of training time (F = 57.45, p < 0.001, and ES = 0.68), showing that EMG RMS amplitude of agonist muscles significantly decreased by 24.2% from pre‐training to post‐training. Additionally, a significant main effect was observed among the agonist muscles (F = 20.80, p < 0.001, and ES = 0.44), highlighting notable differences in different muscle activation levels during the pull‐up performance. Specifically, the RMS amplitudes for BB and BR (p < 0.01), BB and LD (p < 0.01), BR and PM (p < 0.01), BR and PD (p < 0.01), PM and LD (p < 0.01), and LD and PD (p < 0.01) were significantly different.

TABLE 3.

EMG RMS amplitudes (%MVC) of the agonist muscles*.

IRT TRT
Pre‐testing Post‐testing Pre‐testing Post‐testing
BB 66.6 ± 29.5 48.2 ± 12.7 57.1 ± 25.2 52.7 ± 14.7
BR 88.4 ± 31.9 63.7 ± 15.9 95.0 ± 39.0 70.0 ± 14.7
PM 73.6 ± 28.5 47.7 ± 16.2 64.8 ± 22.6 50.3 ± 20.4
LD 92.6 ± 32.3 72.2 ± 28.8 117.2 ± 49.3 85.6 ± 45.6
PD 57.7 ± 18.4 44.4 ± 10.8 55.5 ± 22.9 47.7 ± 10.7
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Note: BB, BR, PM, LD, and PD denote biceps brachii, brachioradialis, pectoralis major, latissimus dorsi, and posterior deltoid fasciculus, respectively. *Indicate significant pre‐training to post‐training changes.

3.5.2. Antagonist muscle coactivation level

Table 4 reveals the EMG RMS amplitudes of antagonist muscles during the pull‐up endurance test before and after training. The main effect of the antagonist muscle factor (F = 119.00, p < 0.01, and ES = 0.82) was identified, showing that the RMS amplitudes of the three antagonist muscles differed from each other. In addition, a significant interaction between the training group and time factors (F = 8.68, p < 0.01, and ES = 0.24) was detected for the RMS amplitudes of antagonist muscles. IRT significantly helped participants in the IRT group reduce the EMG RMS amplitudes by 20.4% (p < 0.01) during the post‐training test compared to pre‐training, whereas TRT did not demonstrate additional differences.

TABLE 4.

EMG RMS amplitudes (% MVC) of antagonist muscles*.

IRT TRT
Pre‐testing Post‐testing p Pre‐testing Post‐testing p
TB 43.5 ± 14.9 34.6 ± 8.2 <0.01* 32.1 ± 9.2 32.4 ± 11.5 0.30
AD 11.8 ± 4.4 8.5 ± 3.5 10.1 ± 3.7 9.7 ± 5.2
MD 19.9 ± 4.4 16.5 ± 4.1 18.6 ± 6.0 15.5 ± 2.9
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Note: TB, AD, and MD denote triceps brachii, anterior deltoid, and middle deltoid muscles, respectively; *Indicate significant pre‐training to post‐training changes.

3.5.3. Antagonist muscle coactivation ratio

The changes in antagonist muscle coactivation ratios before and after training was shown in the Table 5. Independent samples Mann–Whitney tests indicated no significant differences in the coactivation ratios of TB/(BB + BR), AD/PD, and MD/PD pairs between groups before and after training. Paired samples Wilcoxon tests revealed that the coactivation ratios of three pairs in the TRT group did not show significant changes compared to pretraining and post‐training. However, the IRT group experienced a significant reduction of 31.5% coactivation ratio in AD/PD pair, whereas coactivation ratios of TB/(BB + BR) and MD/PD pairs did not demonstrate noteworthy changes before and after training.

TABLE 5.

EMG RMS amplitudes coactivation ratios (%) of antagonist muscles.

IRT TRT
Pre‐testing Post‐testing p Pre‐testing Post‐testing p
TB/(BB + BR) 23.5 ± 11.8 27.9 ± 11.4 0.08 20.2 ± 6.5 25.1 ± 10.0 0.08
AD/PD 21.5 ± 16.9 14.7 ± 7.6 0.03* 15.4 ± 9.5 13.8 ± 6.9 0.98
MD/PD 28.7 ± 18.1 24.0 ± 12.9 0.38 26.7 ± 15.8 25.0 ± 10.2 0.55
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Note: *Indicate significant pretraining to post‐training changes.

4. DISCUSSION

The most important findings of the current study were that both stable and joint instability lat pull‐down resistance training lasted for 8 weeks could significantly improve pull‐up endurance performance. In particular, the IRT group showed superior improvements in pull‐up endurance compared to the TRT group, which is related to significantly lower antagonist muscle coactivation and better movement stability of lat pull‐down movements performed on unstable condition. As far as we know, it is the first study to explore the effects of resistance training with joint instability on improving pull‐up endurance performance.

Up to date, only a few studies have explicitly reported the effects of unstable resistance training on improving muscle endurance performance and the results have not been consistent. For example, in the research of Lima et al. (2018), after the 8‐week push‐up training, the stable group performed 153.3% and 33.8% fewer push‐up repetitions than the group on the unstable Yoak device. Kibele and Behm (Kibele & Behm, 2009) have also demonstrated that unstable resistance training did provide an advantage for improving sit‐ups endurance performance than stable resistance training for inexperienced resistance trainers. However, in the research of Chulvi‐Medrano et al. (2012), the addition of unstable surfaces in push‐up training for 8 weeks does not provide greater improvement in muscular strength and endurance than push‐up training performed on a stable surface in young men. In the current research, the pull‐up endurance performance was all significantly enhanced after 8‐week training compared to baseline tests for both IRT and TRT groups. Specifically, the maximal number of pull‐up repetitions of the IRT group was 45.5% higher than the TRT group. The results were consistent with the research of Lima (Lima et al., 2018), in which the unstable training group showed superior improvements over stable training for neuromuscular efficiency as reflected by a lower antagonist BB EMG activity and lower fatigue indexes with triceps brachii (TB) and serratus anterior (SA) muscles.

In the current research, there was no significant difference in MUAC between pre‐training and post‐training tests for both TRT and IRT group participants, indicating no significant hypertrophy for TB and BB muscles as a result of 8‐week lat pull‐down training on both stable and unstable conditions. The result was consistent with the conclusion that short‐term training programs tend to emphasize neural rather than hypertrophic adaptations (K. Anderson & Behm, 2005; Behm et al., 2010; Sparkes & Behm, 2010). It has been demonstrated that strength gains were mainly attributed to neural adaptations in the first months of resistance training, whereas muscle hypertrophy‐related muscle strength increase began to play roles after at least 12 weeks of resistance training (Häkkinen et al., 1985). The results may suggest that the training gains of the current study may be induced mainly by neural adaptations rather than muscle hypertrophy.

It has been found that the EMG RMS amplitude of each agonist muscle all significantly decreased during the pull‐up endurance test of post‐training compared to pre‐training for both TRT and IRT groups, indicating a lower muscle excitation level relative to MVC after training. Since the resistance load of pull‐ups did not change significantly during the pre‐training and post‐training test, the decline of the EMG RMS amplitude may be mainly due to the increase of the muscle capacity to induce maximum muscle strength, which has been confirmed by the increase of MVIC peak force after training. The decrease of EMG amplitude when performing a constant workload motor task after training was consistent with relevant previous research (Balshaw et al., 2019; Glass & Wisneski, 2023; Holtermann et al., 2005; Lima et al., 2018). It has been suggested that training may prompt the control of muscle activation and regulation in an optimal manner (Baratta et al., 1988; Carolan & Cafarelli, 1992; Dal Maso et al., 2012; Häkkinen et al., 2000), allowing corticospinal inputs of a given intensity to activate fewer motor neurons during a muscle contraction than those recruited before training (Fernandez del Olmo et al., 2006). Therefore, the decrease of EMG amplitude in the present study indicated that the 8 weeks of lat pull‐down resistance training in both stable and unstable conditions can significantly improve the muscle contractility of BB, BR, PM, LD, and PD. Whereas, the training‐related changes in EMG amplitude of agonist muscles showed no significant difference between TRT and IRT groups, indicating that both stable and unstable lat pull‐down resistance training may play the same roles in enhancing agonist muscle contractility.

The difference of training gains between TRT and IRT groups seems to be mainly attributed to the different training effects on antagonist coactivation as a result of training. In the current research, the antagonist coactivation level and ratio of AD/PD pair in the IRT group reduced significantly during the post‐training test compared to the pre‐training test, whereas no significant difference in the antagonist muscle coactivation level or ratio was found in the TRT group. As a lower antagonist muscle coactivation activity may indicate a higher muscle contraction efficiency, the results may demonstrate a superior effect of unstable lat pull‐down resistance training to improve muscle contraction efficiency than training performed on the stable condition.

Actually, it has been proposed that during practice and training, the central nervous system may learn to form a fully formed “internal model” of dynamics in which antagonist muscle coactivation is controlled in a more economical coordination strategy (Gribble et al., 2003; Osu et al., 2002; Wang et al., 2019). As suggested by the research of Carolan and Cafarelli, the 20% decrease in hamstring coactivation could account for a 32.8% increase in net knee extensor torque as a result of training (Carolan & Cafarelli, 1992). Reduced coactivation has been widely accepted as a training‐specific response to increase muscle strength and athletic performance (Wang et al., 2019), although some studies have reported no change in antagonist muscle coactivation after resistance training (Guilhem et al., 2013). Therefore, the results of the current study may indicate that instability conditions exerted during resistance training would prompt the central nervous system to establish a more optimized “internal model” to control the coactivation of antagonist muscles.

In the present research, both groups of subjects effectively increased the number of pull‐up repetitions after 8 weeks of lat pull‐down training under stable and unstable conditions. The results demonstrated that lat pull‐down can be an alternative training maneuver to improve pull‐ups for recreational individuals. It is recommended that coaches use lat pull‐down resistance training to improve strength and endurance in subjects with relatively few pull‐up repetitions. Moreover, resistance training significantly reduced the EMG RMS amplitude of antagonist muscles compared to traditional resistance training and improved the efficiency of muscle contraction and coordination, thereby enabling participants to complete more pull‐ups. Besides, the way we elicit unstable loads with elastic bands in this protocol is easy to replicate in daily teaching and training. It is available for coaches and athletes to incorporate the unstable approach into their training routines to improve movement efficiency.

Absolutely, it should be acknowledged that this study still has several limitations. First, it would be argued that workload should be determined according to the 1RM of the stable and unstable lat pull‐down exercises, respectively. However, in the current research, we were mainly focused on the comparison of stable and unstable resistance training on the pull‐up endurance performance, and thus a constant absolute workload was adopted for the two types of lat pull‐down resistance training exercises to exclude the influence of different workloads on the results. Second, surface EMG data were only collected and analyzed from the upper limbs of the right side and the influence of imbalance performance between left and right sides has not been considered. Third, in this study, we only collected eight main muscles according to previous research, and other muscles, such as trapezius and infraspinatus, have not been tested and analyzed (Dickie et al., 2017; Youdas et al., 2010). Lastly, in the EMG activity assessment, the influence of crosstalk is an inherent concern (Farina et al., 2014). In the current study, we employed a consistent and experienced researcher to position the electrodes according to the previous recommendations, which may help reduce the effects of crosstalk. Nevertheless, the above limitations would reduce the consistency and generalizability of the research findings.

In conclusion, this study demonstrated that an 8‐week of lat pull‐down resistance training performed on stable and unstable conditions can both enhance pull‐up endurance performance. These training gains were associated with increases in agonist muscle contractility as well as muscle contraction efficiency represented by decreases in antagonist muscle coactivation. Particularly, lat pull‐down resistance training performed with joint instability was superior in pull‐up endurance improvement than the stable condition, which may be related to the decrease of antagonist muscle coactivation activities than the stable resistance training method. Future research could further explore the relevant brain mechanisms from a neuroimaging perspective.

CONFLICT OF INTEREST STATEMENT

All the authors disclosed no relevant relationships.

ACKNOWLEDGMENTS

This work was supported by the Shanghai Education Science Research Project (No. C2023195) and the National Natural Science Foundation of China (NSFC) (No. 12272272). The research was approved by the Tongji University Ethical Advisory Committee.

DATA AVAILABILITY STATEMENT

The data used to support the findings of this study are available from the corresponding author upon request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The data used to support the findings of this study are available from the corresponding author upon request.

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