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ORIGINAL ARTICLE
The effects of knee flexion on muscle activation and performance during chin-up exercise
Abdul Muiz Nor Azmi1ABCD, Mohd Syamil Shafiee2ABCDE, Nor Fazila Abd Malek1BCD, Kevin Tan3BCD, Rajkumar Krishnan Vasanthi4CDE, Zulezwan Ab Malik1BCD, Ali Md Nadzalan1ABCDE 1Faculty of Sports Science and Coaching, Sultan Idris Education University, Malaysia 2Ministry of Education, Malaysia
3Faculty of Health and Life Sciences, Management and Science University, Malaysia 4Faculty of Health and Life Sciences, INTI International University, Malaysia
Authors' Contribution: A-Study design; B - Data collection; C - Statistical analysis; D - Manuscript Preparation; E - Funds Collection Abstract
Background Chin-up is an exercise that is done to improve the strength, muscular endurance and size of the and Study Aim upper back and arm muscles. There are many ways to perform chin-up exercises including by performing it with different forms of knee flexion. This study aims to examine the effects of knee flexion on muscle activation and performance during chin-up exercise.
A total of twenty-one healthy trained male (age 20-25 years old) were recruited and were instructed to perform chin-up exercises in three knee conditions: i) knee fully flexed, ii) partial knee flexed, and iii) straight knee. Chin-up performance was measured by the number of repetitions performed in three sets. Muscle activation was measured using EMG and taken from latissimus dorsi (LD), posterior deltoid (PD), and biceps brachii (BB) during both concentric and eccentric phase. One-way repeated measure Analysis of Variances (ANOVA) were conducted to compare the muscle activation and number of repetitions performed across the three variation of chin-up exercise. Findings showed that during the concentric phase, BB recorded higher muscle activation during straight knee compared to knee fully flexed and partial knee flexed, p < .05. In addition, chin-up performance during straight knee and partial knee flexed were better than knee fully flexed, p < .05. The results of this study demonstrated the importance to consider techniques manipulation during exercises due to its effects on acute responses as shown by number of repetitions and muscle activation in this study that might also affect the long-term outcomes.
chin-up, knee, muscle activation, strength, conditioning, performance
Material and Methods
Results
Conclusions
Keywords:
Introduction
Strength and conditioning practitioner often include chin-up into their resistance training
routines. Chin-up is an activity that can strengthen the upper body and muscle mass, especially for bicep brachii, posterior deltoid, pectoralis major, and latissimus dorsi muscles [1, 2]. The chin-up exercise is performed by hanging the entire body from a horizontal bar and then pulling all the way up till the chin is above the bar [1]. During the chin-up, the palms are facing towards the individual.
Like other exercises, changing or manipulating the techniques during the exercise execution may influence the biomechanics of the movement. Previous studies had shown the manipulation of techniques influences movement mechanics of squat [3, 4], push up [5, 6], deadlift [7, 8] and many more. Among the variables of interest to be seen as a result of techniques manipulation includes the muscle activation. Muscle activation reflect the contraction if muscle during certain movement. © Abdul Muiz Nor Azmi, Mohd Syamil Shafiee, Nor Fazila Abd Malek, Kevin Tan, Rajkumar Krishnan Vasanthi, Zulezwan Ab Malik, Ali Md Nadzalan, 2022 doi:10.15561/26649837.2022.0303
Muscle activation could be obtained through the use of electromyography (EMG) method.
EMG is a method for assessing muscle activation in which the EMG detects the amount of neural drive or voluntary activity in a muscle [9]. A previous study has examined muscle activation using EMG between chin-up exercise and lat pulldown [10]. The findings demonstrated that biceps brachii displayed more muscle activation in the concentric phase of the chin-up than the lat pulldown. The results also showed that in the concentric phase, the agonists' biceps brachii and latissimus dorsi exhibited more muscle activation than the antagonists' pectoralis major and triceps brachii.
Chin-up is a type of strength training exercise that is commonly used to assess or to train upper-body strength [11, 12]. As a simple yet challenging exercise to be done, the exercise can be randomly performed in many ways, such as straight knee, partial knee flexed, and knee fully flexed. However, the study that examined chin-up exercise is scarce. Little information is known on how manipulating the knee conditions would affect acute responses such as performance and muscle activation. Therefore,
the study aims to compare the muscle activation of latissimus dorsi, posterior deltoid, bicep brachii, and successful repetition performance during chin-ups using various knee conditions (straight knee, partial knee flexed, and knee fully flexed).
Materials and Methods
Participants
Twenty-one university undergraduate male students aged between 20 to 25 years old participated in this study. Participants are trained men and physically active who have experience in strength and endurance tests. The inclusion criterion of participants involved in the study was that they did not have any previous shoulder injury. Participants will be excluded from the research if they have had a past shoulder injury or any injuries that need rehabilitation sessions.
Before the intervention, participants were given a brief explanation of the research's aims, the procedures to be followed, the risks and advantages of participating in the study. The Physical Activity Readiness Questionnaire (PAR-Q) and a consent letter were completed by the participants before data collection. Participants were informed that they could withdraw from the study at any moment and without having to offer a reason. The Ethics Committee of Human Research at Sultan Idris Education University approved the study.
Procedure
The study employed a repeated measure design. Each participant was asked to perform a chin-up using three different knee conditions (i.e., straight knee, partial knee flexed, and knee fully flexed). Figure 1, Figure 2 and Figure 3 showed the chin-up with three knee conditions. Since the study uses a repeated measure design, there may be sequence effects that influence the participants' behavior (e.g., practice effect or tiredness). The counterbalancing approach can be used to address this problem [13]. Thus, participants were randomly divided into three groups, each with seven people (Group A, B, and C). To ensure that the order of the tasks did not affect the findings, each group performed the chin-ups with different orders of the knee position. Participants in Group A performed the chin-ups starting with a straight knee, partial knee flexed, and knee fully flexed. Participants in Group B completed chin-ups with partial knee flexed, knee fully flexed, and straight knee. Participants in Group C conducted chin-ups with a knee fully flexed, a straight knee, and partial knee flexed. Participants have been tested for chin-up using one knee position in a day to avoid fatigue.
Testing procedure
EMG Marker placement
An EMG device and wireless electrodes (Trigno, Delsys, USA) were utilized to measure muscle
activation based on the SENIAM guidelines. The surface EMG for non-invasive evaluation of muscles (SENIAM) was applied for muscle determination. Before using the EMG, participants were given 10 minutes to warm up. After that, the participants' skin was cleaned using an alcohol swab, as alcohol was allowed to evaporate so that the skin was dry before the electrodes were attached. As sweating might make the electrodes' adherence to the skin deteriorate, the skin preparation was done after the warm-up [1].
The area where the electrodes would be attached was shaved and cleansed for a better placement and touch the needed area. The electrodes were placed to the latissimus dorsi (LD), posterior deltoid (PD), and bicep brachii (BB) muscles on both sides of the participants. During the test period, participants were encouraged to wear comfortable but minimum clothes (short and close-fitting athletic shorts) to increase the accuracy of EMG reading. The mean value of muscle activation level during eccentric and concentric phases was observed.
Protocol
In the ready position, the shoulders of the individual are in a straight position while the feet are in a propped position, i.e. standing on the toes. In this phase, the mortar joint aids movement in the shoulder joint. The elbow closes the angular opening to make it easier for the shoulder to close the chin and this movement is called an elevation movement. At this time, the fingers of the hand grasp the bar with the strength of the digitorum extensor muscle. The chin-up began with the arms straight and completely extended on a bar. The participants must pull themselves up until the chain reaches the top of the bar. The test ends when the participant stops or rests for a while. Participants were asked to repeat these procedures for each knee condition. The number of repetitions for each knee condition was recorded in three sets.
Statistical analysis
The Shapiro-Wilk test was utilized to determine the data normality. The results confirmed that the data was normally distributed. The mean and standard deviation of muscle activation and the number of repetitions during the chin-up for each knee condition were calculated using descriptive statistics. One-way repeated measure analysis of variances (ANOVA) was used to compare the muscle activation and the number of repetitions performed. The significance level was set to p < 0.05. The data were analyzed using Statistical Package of Social Science (SPSS) version 20.
Results
Physical characteristics
Table 1 showed the physical characteristics of participants in this study.
Start
Figure 1. Starting and middle position of straight knee chin-up
Middle
Start
Figure 2. Starting and middle position of partial knee flexed chin-up
Middle
Table 1. Physical characteristics of participants
Variables Mean ± SD
Age (years) 23.50 ± 0.72
Body mass (kg) 68.20 ± 1.02
Height (cm) 170.35 ± 2.10
EMG during concentric phase
Muscle activation in LD, PD, and bicep brachii BB was compared during the concentric phase between straight knee, partial knee flexed, and knee fully flexed (see Table 2). The results of one-way ANOVA demonstrated that there was a significant effect on the BB, F (1, 20) = 301.56, p < .05 during the concentric phase between the three knee conditions. However, there was no significant main effect on the
LD, F (1, 20) = 2.02, p > .05, and PD, F (1, 20) = 1.82, p > .05 during the concentric phase between the three knee conditions.
EMG during eccentric phase Muscle activation in LD, PD, and BB was compared during the eccentric phase between the three knee conditions (see Table 3). The results of one-way ANOVA demonstrated that there was no
Start Middle
Figure 3. Starting and middle position of full knee flexed knee chin-up
Table 2. EMG reading of concentric phase during chin up between positions
EMG Straight knee Partial knee flexed Knee fully flexed
LD mean (% MVIC) 70.50 ± 6.09 72.99 ± 3.15 71.25 ± 6.10
PD mean (% MVIC) 55.10 ± 4.21 56.20 ± 7.47 57.99 ± 5.15
BB mean (% MVIC) 69.38 ± 4.97 b c 61.51 ± 5.21 a 60.35 ± 3.85 a
"Significantly difference from straight knee position; bSignificantly difference from partial knee flexed position; cSignificantly difference from knee fully flexed position; LD - latissimus dorsi; PD - posterior deltoid; BB - bicep brachii; MVIC - maximum voluntary isometric contraction
Table 3. EMG reading of eccentric phase during chin up between positions
EMG Straight knee Partial knee flexed Knee fully flexed
LD mean (% MVIC) 50.71 ± 3.72 51.87 ± 2.39 50.83 ± 2.06
PD mean (% MVIC) 41.76 ± 2.12 40.85 ± 3.83 40.42 ± 4.74
BB mean (% MVIC) 48.01 ± 4.48 48.00 ± 5.37 50.54 ± 6.40
aSignificantly difference from straight knee position; bSignificantly difference from partial knee flexed position; cSignificantly difference from knee fully flexed position; LD - latissimus dorsi; PD - posterior deltoid; BB - bicep brachii; MVIC - maximum voluntary isometric contraction
Table 4. The number of chin-up repetitions using three positions
Variable
Straight knee
Partial knee flexed
Knee fully flexed
Number of repetitions
13.50 ± 0.77c
13.78 ± 0.95c
11.03 ± 0.99ab
aSignificantly difference from straight knee position; bSignificantly difference from partial knee flexed position; cSignificantly difference from knee fully flexed position
significant main effect on the LD, F (1, 20) = 1.63, p > .05, PD, F (1, 20) = 0.32, p > .05, and BB, F (1, 20) = 1.79, p > .05, during the eccentric phase between the three knee conditions.
Number of repetitions
Analysis of the number of chin-up repetitions showed that there was no significant difference between the three knee positions, F (1, 20) = 0.40, p
> .05. Using the pairwise comparison on the number of chin-up repetitions showed that there was a significant difference between the straight knee and knee fully flexed, p = 0.003; and partial knee flexed and knee fully flexed, p = .004. However, there was no significant difference in the number of chin-up repetitions between the straight knee and partial knee flexed, p > .05. Table 4 displayed the mean (SD)
value of the number of repetitions for each knee position during the chin-up exercise.
Discussion
The study aims to compare the muscles' activation and performance during chin-up exercise using a straight knee, partial knee flexed, and knee fully flexed. The findings showed that there was no significant difference in the activation of muscles for LD and PD during the concentric phase between straight knee, partial knee flexed, and knee fully flexed. It shows that LD and PD have the same level of muscle activation when using all three knee conditions. Results in BB showed that straight knee was significantly higher than in partial knee flexed and knee fully flexed position during the concentric phase. Performing the chin-up exercise using a straight knee would produce higher muscle activation in BB during the concentric phase compared to other positions. The muscle activation was also found to be greater during concentric phase compared to eccentric phase, consistent with what has been found in previous study by Doma and Deakin [14], it showed that muscle activation of triceps brachii, pectoralis major, erector spinae, BB and LD was higher when performing chin up in concentric phase might be due to the muscle fibres producing more force during lifting the body upward to overcome inertia compared to the eccentric phase (lowering the body) due to the absence of inertia factor.
Based on the EMG results during the eccentric phase, there was no significant difference between the three knee conditions in LD, PD, or BB. It means that all muscles have the same level of muscle activation in all three positions during the eccentric phase. For the chin-up performance, the straight knee and partial knee flexed position were significantly higher than the knee fully flexed in the number of repetitions. Therefore, this study proves that the use of partial knee flexed and straight knee position are more effective to improve performance and is suitable for muscular endurance training. Furthermore, individuals would generate the similar outcome in both postures, either straight knee or partial knee flexed, throughout the chin-up exercise.
Based on the results, during the concentric phase, doing the chin-up exercise with a straight leg produces more muscle activation in BB. This finding was consistent with a prior study that revealed that
BB produced more muscular activation during chin-ups than lat pulldowns [12]. The stability of the chin-up was a factor in the outcome, as opposed to the lat pulldown. The chin-up exercise is considered unstable because the lower body can move freely when the body is suspended when the hands cling to the horizontal bar. When grasping, the lower arm muscles (flexor and extensor carpi radialis) exert a lot of traction, which leads the BB muscle to activate a lot [15].
The LD was shown to have the highest percentage of muscle activation throughout the concentric and eccentric phases in all three knee conditions, followed by the BB and PD. The findings were supported by the previous study where Doma and Deakin [10] found that during the chin-up and lat pulldown exercise, both exercises produced greater muscle activity in the agonists' LD and BB compared to the antagonists' pectoralis major and triceps brachii. A previous study also found that supinated grips stimulated more BB, while pronated grips activated more LD [12, 16].
The current study findings add the knowledge on how manipulating techniques during an upper back exercise affect the muscle activation and performance by individuals [17, 18, 19, 20]. More study is warranted to be conducted on the chronic effects of the exercises performed in various techniques manipulation on physical and physiological adaptation.
Conclusions
This study demonstrated that the BB muscle shows the average production of the highest average level of muscle activation while performing chin-up activity using a straight knee in the concentric phase. The LD and PD muscles demonstrate identical muscular activity when performing the chin-up in concentric and eccentric phases. The combination of partial knee flexed and the straight knee is the most beneficial for enhancing performance and is excellent for muscular endurance training. Therefore, the coach must realize that each method used will change the movement's acute impacts, which are supposed to have a long-term impact.
Conflicts of Interest
The authors declare no conflicts of interest.
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Information about the authors:
Abdul Muiz Nor Azmi; https://orcid.org/0000-0002-2405-1369; [email protected]; Faculty of Sports Science and Coaching, Sultan Idris Education University; Tanjong Malim, Malaysia.
Mohd Syamil Shafiee; https://orcid.org/0000-0003-2420-975X; [email protected]; Ministry of Education, Malaysia; Putrajaya, Malaysia.
Nor Fazila Abd Malek; https://orcid.org/0000-0001-8998-228X; [email protected]; Faculty of Sports Science and Coaching, Sultan Idris Education University; Tanjong Malim, Malaysia.
Kevin Tan; https://orcid.org/0000-0003-3676-5614; [email protected]; Faculty of Health and Life Sciences, Management and Science University; Shah Alam, Malaysia.
Rajkumar Krishnan Vasanthi; https://orcid.org/0000-0001-6866-8224; [email protected]; Faculty of Health and Life Sciences, INTI International University; Nilai, Malaysia.
Zulezwan Ab Malik; https://orcid.org/0000-0002-7817-0574; [email protected]; Faculty of Sports Science and Coaching, Sultan Idris Education University; Tanjong Malim, Malaysia.
Ali Md Nadzalan; (Corresponding author); https://orcid.org/0000-0002-0621-2245; [email protected]. edu.my; Faculty of Sports Science and Coaching, Sultan Idris Education University; Tanjong Malim, Malaysia.
Cite this article as:
Azmi AMN, Shafiee MS, Malek NFA, Tan K, Vasanthi RK, Malik ZA, Nadzalan AM. The effects of knee flexion on muscle activation and performance during chin-up exercise. Pedagogy of Physical Culture and Sports, 2022;26(3):158-164.
https://doi.org/10.15561/26649837.2022.0303
This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/deed.en).
Received: 26.04.2022
Accepted: 20.05.2022; Published: 30.06.2022
