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Muscle Activation during Different Sit-up Exercises: An Electromyographical Study Hussain, I., Sharma, K., Ahsan, M. & Ansari, N.W. |
Abstract The perfect execution of exercises expands the maneuverability of the intended musculature of a sportsman. Indian trainers, coaches, physical educators and athletes often tend to copy the world-class champions, athletes and performers as research in this field in India has thus far been limited. Copying has become a cyclic trend, which has not revolutionised the result of the designed exercises. This study was designed to electromyographically analyse muscles activation during different abdominal exercises to be performed for maximum advantage. The electromyography amplitudes of contraction of the rectus abdominis, internal oblique and external oblique during three different sit-up exercises were recorded. Ten male subjects selected for the experiment were of All India Intervarsity Level from Aligarh Muslim University, Aligarh. Their mean age, height and weight were 21.4 yrs, 167.4 cm and 62.6 kg respectively. The Student Physiograph was used for EMG recording and all procedures were standardised. Three sets of observations were made on each subject. The electrodes were located over the belly of the muscles and oriented along its longitudinal axis. The sit-up exercises were executed to 720 angles. The undertaken sit-up exercises were analysed by ANOVA. The concentric and the eccentric phase of exercises were examined by paired t-test and compared with statistical significance at 0.05 levels. The time pulse was synchronised to angles of movement. The Optimisation technique was used to obtain the angle of maximum contraction intensity. Results of the research indicates that different quadrants contract optimally at different angles. Our findings support the concept that abdominal strengthening exercises can differentially activate various abdominal muscle groups, but contradict some traditionally held assumptions regarding the effects of specific exercises. Introduction An essential ingredient to the type of complete physique for any sports performance is a trim and well developed anterior midsection (abdominal). The anatomical and kinesiological review of literature of the anterior midsection reveals that the rectus abdominis is the rigid muscle wall across the entire front of the abdominal. It has a crenellated, washboard like appearances, in fact when optimally developed, it can be one of the most highly detailed areas and sharply defined in entire physique. Primarily, the actual muscle that must be developed through strong, scientific and consistent training are those that that control the abdominals. Efficacy of exercises requires practice steming from an acknowledged theoretical model of the functioning organism and must be supported by research designs. However, in India, research is scarce in the field of sports and exercise training. Acute mechanical and methodological issues, along with the complexity of muscular contraction patterns, have imposed limitations on operative research. In addition difficulties in accurately locating the complex muscular actions and force reproduction have been limiting. The abdominal muscle acts virtually in every thing that one does. The abdominals help to stabilise your upper body and acts as a bridge between upper and lower body in sequential transfer of load in motor activities of every day life and rigorous sports activity. The right approach to abdominal training will be of incredible value in achieving the physical goals of sportsman and woman. It is difficult to isolate action to any particular section of the rectus abdominis but there are general rules for which area of the frontal abdominis wall is worked by various types of movement: the upper section works hardest in sit-up work, while various type of leg raises work the lower part of the muscle more intensely. However, recent research has indicated that there are differences in electrical activity in various parts of rectus abdominis. The largest and most frequent force generated within body is by contraction of muscles. Normally, muscles do not contract alone because this would produce a stereotype nonfunctional motion. The role of individual muscle, or a group of muscles in producing movement or stabilising body segments, may be examined by palpating the muscle to judge when it is active and relaxed but there is no record for analysing the timing or magnitude of muscle contractions. Most abdominal exercises designed have been merely empirically derived. Sometimes new procedures have presented as promising, but they have lacked firm theoretical and methodological basis. Electromyography (EMG) has been an important tool in helping to understand proper exercise executions and effects produced on the designated muscle. The onset, duration and peaks of the muscular activity are seen on the EMG. The development of amplifying and recording equipment during World War II made it possible to use improved methods for the study of muscular activity in living human subjects. Eminent researchers and scientists (Inman, 1952; Ralston, 1960; Basmajian, 1978 and Heckathorne, 1981) reported that the sequence of activation and relaxation as well as the relative amount of activity performed by particular muscles produced various isolated and coordinated functions. The recorded amplitude of muscle action potential bears no quantitative relationship with muscular tension (Pocock, 1963). There is a direct linear relationship between integrated EMG and isotonic tensions if the velocity of the movement is held constant (Bigland and Lippold, 1954). Comparatively few Electromyographical (EMG) studies have been done on the abdominal muscles in the applied field of sports and exercises. EMG has been an important contrivance in helping to understand electrical characteristics of muscle and muscular contraction and explore its uses in motion analysis. EMG provides a measure of the level of muscle activation and has been used to evaluate synergistic patterns associated with exercises. Using surface electrodes for this type of study seems well established. Most of the previously mentioned comparative studies have used surface electrodes (Francis and Scott, 1974; Gough and Ladley, 1971; Jackson, 1973). Alington, et al (1966) used both surface and needle electrodes side by side and found that they produced similar results. Bouisset and Maton (1972), found a linear relationship between integrated EMG activity collected by surface and intra-muscular electrodes. However, the main emphasis in this study is not only the integrated EMG changes but also on the differences in functional output of amplitudes of the muscles of the abdominal at different phases and angles of movement (sit-up exercises). Methodology Participants Ten (10) male All India Intervarsity level players (Football, Hockey and Athletics) from Aligarh Muslim University, Aligarh, volunteered as subjects in the experiment. They range in age from 19 to 24 years (mean of 21.4 years). Prior to testing, all the subjects were informed of the nature of the tests and the appropriate consent was obtained. Surface EMG was recorded from the abdominal muscle using bipolar electrodes. Electromyographic recordings were made of the right abdominal muscles. Descriptive anthropometrics data are provided in the Table 1. Apparatus The Student Physiograph (Biodevices, Ambala) was used for the experiment. Because of the equipment limitation, only one muscle (quadrant) could be recorded at a time. Prior to the subject’s arrival in the laboratory, the instruments were calibrated. The sensitivity for EMG recording was set at 100µv and the paper speed was set at 25 mm/sec. The frequency cut-off marked at 3 Hz. The diameters of the bipolar electrodes were 1.3cm. Procedure The study defined the quantitative characteristics of the abdominal muscles during different abdominal exercises. The measurement record included the amplitude, frequency and time in response to standard procedure. There was no way of measuring the velocity of the movement during exercise but an attempt was made to control the velocity by establishing a set rhythm for performance. The players were given practice of the different variations of abdominal exercises and all were performed with three counts. Subjects were trained to perform the exercises on the count one, two and three. The players practiced for a period of two weeks to do the abdominal exercises in a sequence of beats of watches (along with the counts). The watch beats has been amplified and the exercises were continued at that beat sound. Table 1. Anthropometric Description
No. Subjects | Gender | Age (yrs) | Height (cm) | Weight (kg)
10 | Male | 19-24 | 165-169 | 56-64
The experimental instructions to subjects were as follows: on ‘ready’ subject are to make themselves ready and attentive; on ‘go’ they had to start the abdominal exercises with the count of beat as ‘one’, ‘two’, and ‘three’ (upward), ‘four’, ‘five’ and ‘six’ (downward). The concentric and eccentric phases of the exercise were considered and the eccentric phase was recorded for the second set study. The players performed the following abdominal exercises: (i) Straight Leg Sit-up, (ii) Bent Leg Sit-up, and (iii) Crunches. The reading was recorded for three repetitions to avoid the effect of fatigue and all exercises were performed with an interval of 3 to 5 minutes. Firstly, the abdominal reflexes were elicited while subjects performed the exercises. To determine appropriate electrode placement, the palpation techniques described by Smith, Weiss, and Lehmkuhl (1996) were used. The skin over the target muscles was abraded and cleaned to assure low skin resistance. After the setting up of frequency, paper speed, etc. the electrodes were prepared using conducting gel and the proximal electrodes placed directly over the belly of the designated muscle. The electrodes’ position was maintained consistent from subject to subject. Electrodes were placed distally in line with the muscle fibers. Both sets of electrodes were centered from medial to lateral. The ground electrode was secured slightly superior to the lateral malleolus of the right leg. Electrodes were placed in the Upper Umbilicus and Hypogastria of the rectus abdominis and the external oblique and internal oblique muscles. Electrodes for the external oblique were placed between the lower edge of the rib cage and the anterior superior iliac spine, in a line directly superior to the latter. The electrode on the internal oblique was placed in a small triangular area bounded by the lateral edge of the rectus, the inguinal ligament and a line connecting the Umbilicus and the Anterior Illiac spine. The exact site of placement was immediately inferior to a transverse line through the anterior superior Illiac spine. It is known that during sit-up exercises, the body does not move with the same velocity through out the range of motion. As the change of velocity is very small, the researchers tried to control by reducing and keeping the velocity constant throughout the range of motion. To coordinate the time pulse and motion angles, utmost care was taken that rhythm of the one, two and three count coordinated at mentioned angles. The sit-up exercises were executed to an angle of 72° (degrees). An angle marked scale was constructed using a goniometer and were placed at 24°, 48° and 72°. The base line scale was placed in the line of the segmental line joining the shoulder axis and hip axis for torso motion and for leg motion the scale was placed in line with the hip axis and lateral Malleolus point axis. In this study, the averaged of frequency, duration and amplitudes were used, using the technique of quantification described by Kelley (1971). Then EMG signal was analysed on the basis of amplitude and time. The amplitude was simply defined as the height of the wave and the time pulses were coordinated with the angles of movement. The optimum EMG amplitudes have been taken as feedback to the corresponding time pulse to generalise the contraction intensity of the muscle. The EMG time and amplitude recordings were synchronised to that of the angles. The measures of average amplitude at every angle were measured to compute the mean value of the sample. These means were subjected to Optimisation Technique to identify the angles at the optimum contraction intensity (amplitude). A program for Optimisation Technique has been developed to operate in FORTRAN-77. Results The performance scores of the first set were subjected to analysis of variance (ANOVA) for repeated measures. A separate analysis of variance (ANOVA) with repeated measures was calculated for each of the four individual muscles. The EMG amplitudes measures for each position for the Rectus abdominis (Upper Rectus and Lower Rectus), Internal Oblique and External Oblique as a whole are presented in Table 2. Statistical study of the ANOVA table confirmed that significant differences were obtained between EMG amplitudes of different groups of muscles [F=8.28; p<0.05; Tab. F=6.94]. The analysis indicated that the different types of abdominal exercises were not significant [F=1.92, p>0.05]. The recordings for all the different abdominal exercises i.e. Straight Leg Sit-up, Bent Leg Sit-up and Crunches were found to be homogenous. While there were differences between different sets of exercises, there were not significant enough to recommend one being the best abdominal exercise for the anterior abdominal muscles. Further statistical analysis shows the differences between the different abdominal muscles with significant differences found between the Rectus abdominis (Upper and Lower Rectus) and Oblique (External and Internal Oblique). There were noted significant difference between the Upper Rectus and Internal Oblique; Upper Rectus and External Oblique; Lower Rectus and Internal Oblique; and Lower Rectus and External Oblique. There were no significant difference between Upper Rectus and Lower Rectus and no significant difference between Internal Oblique and External Oblique. The different sets of exercises showed a very marked activity difference in different groups of muscles. Table 2. The mean values of the average EMG output in Amplitudes
| UR | LR | IO | EO
SLS | 10.00 | 10.51 | 6.54 | 8.4
BLS | 11.10 | 9.52 | 8.47 | 8.79
CR | 10.00 | 12.00 | 9.26 | 8.82
Upper Rectus (UR), Lower Rectus (LR), Internal Oblique (IO) and External Oblique (EO) Straight Leg sit-up (SLS), Bent Leg Sit-up (BLS) and Crunches (CR) The data of all the rectus quadrants (Epigastria (Epi), Upper Umbilicus (Up.umbi), Lower Umbilicus (Lo.umbi) and Hypogastria (Hypo)) of rectus abdominus were put onto the Optimisation Program developed to identify the angle of highest intensity of contraction during the sit-up exercises. The result revealed that the intensity of the muscular contraction during sit up exercises varied at different angles of motion. The amplitudes means of the different quadrants varies. The result indicate that in Straight Leg Sit-Up exercise. The maximum angle is 44.05° for Lower Umbilicus and 34.83° for Upper Umbilicus. The Epigastria and Hypogastria act at maximum between these ranges. In the case of Bent Leg Sit-Ups, the maximum contraction intensity is at 36.25° for Lower Umbilicus and 32.27° for Hypogastria. The Epigastria and Upper Umbilicus act between these two angles of motion. The Crunch has 38.09° for Lower Umbilicus and 31.78° for Epigastria while doing Crunch 38.09° is maximum angle. Concentric and eccentric phases of muscular contraction during the sit-up exercises were subjected to statistical analysis. The mean EMG amplitude values were analysed using a paired t-test for each of the 3 exercises. Reported differences were accepted as statistically non-significant at p > 0.05. The statistical analysis paired t-test showed no significant differences between the concentric and eccentric phase of contraction during the sit-up exercises. The mean EMG data showed variations that for each exercise tested in the Upper Umbilicus (Up.Um.) and Hypogastria (Hypo) region of the rectus abdominis. Table 3. Angle identification
| Epi | Up.Umbi | Lo.Umbi | Hypo
SLS | 35.37° | 34.83° | 44.05° | 35.92°
BLS | 33.89° | 34.84° | 36.25° | 32.27°
CR | 31.78° | 36.32° | 38.09° | 35.31°
Epigastria (Epi), Upper Umbilicus (Up.Umbi), Lower Umbilicus (Lo.Umbi) and Hypogastria (Hypo) Straight Leg sit-up (SLS), Bent Leg Sit-up (BLS) and Crunches (CR) Table 4. The mean values of the EMG Amplitudes of Concentric and Eccentric phase of Abdominal Exercises in Rectus Abdominis muscles
| Upper Umbilicus | Hypogastria
Con. | Ecc. | Con. | Ecc.
SLS | 10.00 | 8.70 | 10.51 | 9.67
BLS | 11.10 | 9.97 | 9.52 | 8.86
CR | 10.10 | 9.31 | 12.00 | 11.49
Concentric (Con), Eccentric (Ecci) Straight Leg sit-up (SLS), Bent Leg Sit-up (BLS) and Crunches (CR) During the straight leg sit-up, the Upper Umbilicus showed a mean differences of 1.35 (con.-10.00 & ecc.-8.70). The same muscle, during a bent leg sit-up, showed a mean difference of 1.13 (con.-11.10 & ecc.-9.97) and of 0.69 (con.- 10.00 & ecc.-9.31) for the crunch exercise. All mean values were not significantly different from each other. The Hypogastria region during straight leg sit-up exercise showed a mean differences of 0.84 (con.-10.51 & ecc.-9.67), bent leg sit-up of 0.66 (con.-9.52 & ecc.-8.86) and the crunches is of 0.51 (con.- 12.00 & ecc.-11.49). All mean values were not significantly different from each other. Table 5. Statistical analyses of concentric and eccentric phases of Sit-up Exercises
Straight Leg Sit-ups | Cal.-t | Bent Leg Sit-ups | Cal.-t | Crunches | Cal.-t
Upper Umbilicus | 1.41 | Upper Umbilicus | 1.43 | Upper Umbilicus | 0.77
Hypogastria | 0.63 | Hypogastria | 0.46 | Hypogastria | 0.29
Tabulated t-value: Tab.t = 2.26 Significant = Cal.t > tab.t Non Significant = Cal.t < tab.t Discussion Of the wide range of exercises claiming to tone and strengthen the abdominal muscles, many of these are inadequate and ineffective. Some exercises may actually lead to lower back pain and do little to strengthen the abdominals. The purpose of this investigation was to provide accurate, useful information and exercise guidelines for abdominal training. In addition, several myths and misconceptions about abdominal training have been dispelled. The result of this investigation reveals that abdominal exercises do affect the degree of activity of the rectus abdominals and oblique muscles. It is clear that the rectus abdominis, by its amplitudes of the activity, is a stronger mover in abdominal exercise, while the obliques are not as strong. The most significant findings of this investigation were the greater amount of activity in the lower rectus compared to that of upper rectus. The reason for this may be the difference in stability of the insertion of the two portion of rectus. The insertion of the upper fibers, to the rib cage, is relatively mobile compared to that of the insertion of the lower rectus (Symphysis Pubis). This difference in mobility may have affected the action of the upper rectus. Full sit-ups involve the hip flexors, which may cause the lower back to arch and unwanted back pain, particularly in individuals with relatively weak abdominals (Mutoh, Mori, Nakamura & Miyashita, 1981). Leg-raising exercises in a supine position challenge the hip flexors with limited involvement of the abdominals (Libetz & Gutin, 1970). Frequently, there is a muscle imbalance between the weaker abdominals and the stronger hip flexors in trunk flexing movements (Kendall, McCreary & Provance, 1993). The goal of abdominal training is to maximise the involvement of the abdominals, while minimising the involvement of the hip flexors (Walters & Partridge, 1957). Partial sit-up or crunch exercises, with the knees flexed and ankles unsupported, are the best for strengthening the abdominal muscles, without risk to the lower back (Mutoh et al., 1981). When performing some abdominal exercises, it often feels like the muscle is divided into an upper and lower section. Although the abdominal muscles have inter-segmental nerve stimulation, you are not able to contract one section independent of the other. However, when the hips are stabilised and only the trunk is lifted, there is relatively more muscle shortening in the upper abdominal region, which leads to greater muscle activation in that region (Walters & Partridge, 1957). Perhaps one of the most common and important questions asked about abdominal training is “How high up should you going in a crunch (or curl-up)?” Research suggests that the abdominals flex the spinal column for about the first 30 to 45 degrees of movement, which is approximately equivalent to lifting your shoulder blades off the ground (Laban, Raptou & Johnson, 1965; Plowman, 1992; Rasch & Burke, 1978; Ricci, Marchetti & Figura, 1981). Due to the potential pressure placed on the lower spine by the hip flexors, full sit-ups cannot be recommended. Plowman (1992) adds that bent knee, feet supported sit-ups may cause lumbar stress, which could lead to harmful effects on the lumbar discs. Several studies indicate that supine crunches, with bent knees and unsupported legs, maximise abdominal activity and minimise hip flexor (specifically the rectus femoris) activity (Godgrey, Kindig & Windell, 1977; Guimaraes et al., 1991; Libetz & Gutin, 1970; Walters & Partridge, 1957). Since the effectiveness of the abdominal exercises is within this small range of motion (30 - 45 degrees), more repetitions may have to be performed to appropriately challenge these muscles. This study supports previous findings that there is no significant difference in abdominal muscle intensity between the concentric and eccentric contraction for any traditional abdominal exercises i.e. where any external resistance during the course of exercises is not added. In addition, there is an increase in abdominal muscle activity during the course of exercise execution. The principal reason for lower (non-significant) abdominal activity in the eccentric phase than the concentric phase is that the vertical lift against the gravitational force provides enough resistance to require substantial muscle recruitment in concentric contraction. The findings are similar to those reported by Clark et al (2003). Minimal abdominal muscle recruitment is required while performing downward motion (eccentric) in a supine lying position as enough load to require comparable abdominal muscle activity is produced due to the controlled motion as recorded during the abdominal exercise. The generation of muscles activation increases with lowering of velocity of the movement. In order to provide greater overload to the abdominal musculature on a traditional abdominal exercise, additional resistance must be provided. In summary, all abdominal exercise elicited abdominal muscle activity during concentric and eccentric phase of contraction when used with proper technique. The perfect way to perform an abdominal exercise is to elicit significantly greater abdominal muscle recruitment. Practical Applications The results of this study verify that abdominal exercises used in a supine position elicit abdominal muscle activity when performing a traditional abdominal exercise. As the different traditional techniques of abdominal exercises do not differ significantly in the activation of the designated muscles, any one of these exercise techniques may be performed to enhance strength and/or endurance. The research results have revealed that the sit up exercise must be executed to a maximum angle of 45.00° and minimum of 31.78°. Hence the abdominal exercise should be performed to 45.00° angle for better effectiveness and productive value. As there is no significant difference between the concentric and eccentric phase of contraction during the selected abdominal exercises, the eccentric phase of contraction should be performed religiously, because the eccentric phase of contraction can maximise the force exerted and the work performed by the muscle; associated with a greater mechanical efficiency. The mechanical effects of impact forces can attenuate and reduce the tissue damage, pain and injuries associated with exercise. References Alfredson, H. 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Wilkins, H.A., Petersen, S.R., Bagnall, K.M. Wessel, J. Quinne H.A. & Wenger, H.A. (1988). The influence of isokinetic concentric resistance training on concentric and eccentric torque outputs and cross-sectional area of the quadriceps femoris. Can. J. Sport Sci. 13: 76-77. Acknowledgments We greatly appreciate the cooperation and interest of the staff of the Department of Physiology, NMC, AMU, Aligarh. Our special thanks are extended to Prof. Rajendra Singh, Director, Jiwaji University, Gwalior; Prof. Tariq Aziz, Department of Applied Mathematics, AMU, Aligarh; Dr. Rajiv Gulati, Dr. Sangita Sahgal, D/O Physiology, JNMC, AMU, Aligarh; Dr. Athar Ali Moinuddin, Department of Electronic, Z.H.Engg.College, AMU, Aligarh; Dr. Haseeb Athar, Dept. of Statistics, AMU, Aligarh; Mr.Somvir Sharmr (STA), JNMC, AMU, Aligarh; for their contributions in the data collection, interpretation, processing and altruistic support in completion of the experiment. Contact Dr. Ikram Hussain Department of Physical Health & Sports Education Aligarh Muslim University Aligarh, India. ikram1691@yahoo.com Dr. Kalpana Sharma Noida College of Physical Education Jawahar Navodaya Vidyalaya Road DhoomManikpur, GBN Uttar Pradesh, India. drkalpanas@gmail.com Ahsan, M. and Ansari, N.W Research scholar, Department of Physical Health & Sports Education Aligarh Muslim University Aligarh, India. http://www.icsspe.org/portal/index.php?w=1&z=5 Muscle Activation during Different Sit-up Exercises: An Electromyographical Study Hussain, I., Sharma, K., Ahsan, M. & Ansari, N.W.