Evaluation of trunk muscle activities in response to three breastfeeding positions utilised by women

1. Introduction

Breastfeeding (BF) is the normal way of providing young infants with nutrients they need for healthy growth and development [1]. BF has been associated with several maternal [2, 3] and infant [3, 4] benefits. As a result, it has been widely recommended as a safe practice. The World Health Organization (WHO) [1] has recommended two years breastfeeding with first 6 months of exclusive breastfeeding and more than 8 times breastfeeding of the baby per day in the first 3 months of an infant’s life. In response, campaigns on promotion of BF practices are increasing in most clinical and non-clinical settings. Most hospitals have engaged in baby-friendly initiative programme and have been shown to represent important channels for dissemination of BF knowledge and practice [5]. Empirical evidences and anecdotal observations have shown increased compliance with breastfeeding recommendations among Nigerian women [6, 7, 8] as well as in other parts of the world [9, 10].

However, some adverse maternal health conditions have been associated with BF practices, most of which include mastalgia [11], breast infections [12], reduced bone mineral density [13] and musculoskeletal pain [14, 15, 16]. Breastfeeding-related musculoskeletal pain has been associated with faulty posture [14, 15, 16, 17] and several studies had reported the adoption of ergonomically unsuitable BF postures among nursing mothers [7, 16, 18]. The prolonged duration and frequency of BF tasks also has great potentials of further eliciting musculoskeletal disorders.

Several breastfeeding positions have been recommended [19, 20] for effective BF practices with maximized maternal and infant benefits. The cradle, cross-cradle and football/clutch holds have been widely recommended [19, 20, 21, 22, 23] and utilized by mothers [7, 15].

The cradle (C1), cross-cradle (C2) and football (FB) BF holds are performed in upright sitting although with different arrangements. C1 hold involves supporting the infant with the upper limb closer to the reference breast while holding the breast with the contralateral hand [20]. Conversely, C2 hold involves supporting the infant with the upper limb contralateral to the reference breast while holding the breast with the ipsilateral hand [20]. The FB hold is similar to tucking the baby under the arm like a football with the baby’s feet extending across the body. The baby’s head and shoulders are supported with the hand on the same side of the feeding breast [20].

These BF hold positions have been uniformly recommended and none of these positions have been ranked most effective than the others although some situations or health conditions may require utilization of a particular BF hold over others. For instance, C1 hold has been regarded as the most suitable position for full-term babies who were delivered vaginally and may induce abdominal pressure in mothers with caesarean [22]. C2 hold is advised for small babies and infants who have latching problems [22]. FB hold is suitable for women with Caesarean section to avoid the baby resting on the stomach as well as those with large breasts or flat nipples. It is also a preferred method for feeding twins, small infants or those who have troubles latching on. However, there is paucity of studies on the efficacy of these BF holds towards safe BF practices. Considering the wide recommendations of these BF hold positions and the prevalence of breastfeeding-related musculoskeletal disorders, there is need to evaluate the biomechanical implications of these BF holds so as to delineate their ergonomic suitability. This study was therefore designed to evaluate the electromyographic (EMG) activities of the trunk muscles in response to the C1, C2 and FB hold positions.

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Twenty healthy young nulliparous non-pregnant females (18–35 years) were recruited to participate in this study. All the participants were right handed, had no previous engagement in physical exercise activities as well as reported no history of musculoskeletal disorders, particularly spinal or upper limb pain or injury. The study protocol was approved by the University of Nigeria health research ethics committee. After being informed of the purpose and procedures of the experiment, the participants signed a written informed consent form. The study was conducted in the kinesiology laboratory of the Department of Medical Rehabilitation, University of Nigeria, Enugu, Nigeria.

The study protocol consisted of a preparatory phase and an experimental phase. During the former, habituation to the experimental procedures was performed. This was achieved by exposing participants to pictorial representations and video clips of the three breastfeeding hold positions while they adopted the positions severally until they were mastered, to the satisfaction of the researchers. Subsequently, the right and left external oblique (EO) muscles, and the right and left thoracic erector spinae (ES) muscles were located and marked off. The skin lying over the muscles, shaved where necessary, were wiped with alcohol. Pairs of silver-silver chloride surface electrodes were placed on the skin over each muscle belly, longitudinally to muscle fibres with an inter-electrode distance of 1 cm. The electrodes were placed 5 cm lateral to the T9 spinous process for the right and left ES muscles, respectively and 15 cm from the umbilicus for the left and right EO muscles, respectively. These electrode placements have been shown to be representatives of the underlying muscle activity to within 15% root mean square of maximum voluntary contraction [24].

In the experimental phase, the participants completed 3-min maximum voluntary contraction (MVC) tests for each muscle, each of which was repeated twice with a 2-min rest period between trials. MVC positions and techniques were as adopted from Vera-Garcia et al. [25]. To generate MVC for the ES muscles, the participants were in supine lying with the upper trunk suspended and the hips positioned at the edge of the plinth. With the arms crossed over the chest for stability and prevention of associated and trick movements, participant’s legs were stabilized using a strap attached to the plinth while an assistant stabilizes the knees. Manual resistance was applied to the back by applying a downward pressure on the shoulder blades as the participant tries to extend the back contracting the erector spinae muscles against the resistance. For the EO muscles, participants attempted to laterally flex the upper trunk in the frontal plane from a side lying position, with the knees bent and strapped with a belt across the plinth and further supported manually by an assistant. Crossing the arms in front of the chest with a fully flexed elbow and manually braced by the researcher, an inferior-directed manual resistance was applied to the superior shoulder and elbow as the participant tries to lift herself from the plinth. Participants were verbally encouraged during the maximal isometric efforts.

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Subsequent to the MVC tests, the baseline muscle activities of the right and left erector spinae and external oblique muscles were measured in a relaxed sitting position before commencing the BF trials.

To avoid the potential effect of fatigue, the order of the trials was randomized. For the C1 hold, the participant sat upright, back supported on the back rest of the chair with hips and knee flexed at 90 ∘ , hips slightly abducted and feet placed flat on a foot support. A simulated infant (Jimmy, weight – 6 kg; length – 49 cm) was placed in a right side lying position on a supporting pillow placed on the participant’s thigh. Jimmy’s was positioned on the crux of the participant’s left upper-limb as her left elbow supported Jimmy’s head with the left palm placed on his buttocks. The participant’s right hand [contralateral (CL) hand] grasped the left breast, thumb above the nipple and other fingers below the nipple as it was directed towards Jimmy’s mouth gentle, maintaining eye contact with him. For the C2 hold, participant and Jimmy maintained similar starting positions as in C1 but Jimmy’s head was supported by the participant’s right hand while her left hand [ipsilateral (IL) hand] grasped her left breast during the simulated feeding. For the FB hold, participant adopted same sitting position (as in C1 and C2 holds), moved towards the right side of the chair with a pillow placed on her left side, parallel to the left thigh.. Jimmy was positioned in supine lying on the pillow with his head towards the left breast. The participant placed her along Jimmy’s right side while supporting his head with her left (IL) hand, as if clutching a football. She then leaned forward, bringing the IL breast closer to Jimmy while directing the nipple towards his lips with the CL hand. Each BF hold trial was maintained for 5 mins with a 30-min rest period between trials.

During each trial, EMG signals were recorded from the ES and EO muscles and were pre-amplified by a pre-amplifier placed close to the electrodes while signals were sent to the data acquisition unit of a Myoplus2 system (Neurotrac System, Verity Medicals, Hampshire, UK), which amplified and sampled the EMG inputs at 1000 Hz. The EMG data were analyzed using a Neurotrac software (version 5.0.117) and normalized relative to the MVC values. On a chart of labeled human body parts, participants were also asked to report any body discomforts experienced during each BF trials by responding either Yes or No.

The ratios of right (CL) ES to left (IL) ES (CL ES:IL ES ratio) muscle activation as well as CL EO to IL EO (CL EO:IL EO ratio) muscle activation were used to make inferences about postural symmetry/asymmetry. A ratio of $>$ 1, indicates that there was more muscle activity in the CL ES or CL EO, respectively; a ratio of 1, indicates more muscle activity in the IL ES or IL EO, respectively while a ratio equals 1 indicates symmetry/equal muscle activity on both sides of the body.

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Data were summarized using descriptive statistics of mean, standard deviation, frequency and percentage. Statistical analysis was performed using a one-factor repeated measures analysis of variance (ANOVA) model. Bonferroni post hoc analysis was performed to identify specific differences between multiple pairwise comparisons. Spearman rank correlation was also used to ascertain the correlations among muscle activities and participants’ self-reported discomforts. All significance levels were 0.05, and SPSS version 20.0 (SPSS, Chicago, IL, USA) was used for the statistical analyses.

4. Results

Participants’ mean ± standard deviation age, weight, height, body mass index (BMI) and bust circumference (reference point- nipples) were, respectively, 21.10 ± 1.65 years, 60.83 ± 9.91 kg, 1.73 ± 0.06 m, 20.31 ± 2.83 kg/m 2 and 86.98 ± 5.69 cm. EMG data collected from the four muscles (CL EO, IL EO, CL ES and IL ES) were averaged. The normalized EMG data of the four muscles during relaxed sitting and the 3 BF trials are presented on Table 1 above. For all the muscles, there significant differences in their EMG data across the resting and 3 BF hold positions. The C2 hold elicited the highest muscle activities in the CL ES and EO muscles, as compared to the C1 and FB holds. C1 hold elicited the highest muscle activity in the IL ES and EO muscle, as compared to the C2 and FB holds.

Table 2 shows comparisons among asymmetry ratios of the studied muscles. There was a significant difference in the RT EO: LT EO ratio across trials with C2 eliciting the highest asymmetry in these muscles. In all the BF hold positions, the RT EO muscles were more active than the LT EO muscles. However, there was no significant difference in the RT ES: LT ES ratio across the trials.

Participants’ self-reported discomforts during the 3 breastfeeding hold positions are presented on Table 3 below. The highest frequency of body discomforts were reported in the upper limb contralateral to the nursing breast (the right upper limb in this case) with majority (65%) of the complaints recorded during the C2 hold position. Body discomforts were also recorded in the right neck region, next to the right upper limb discomforts, the complaints recorded during the FB (55%), C1 (50%) and C2 (50%) holds.

Furthermore, there was no statistically significant relationship ( $p>$ 0.05) among the muscle activities and self-reported discomforts during each of the BF tasks.

This novel study investigated erector spinae and external oblique muscle activities during three recommended breastfeeding hold positions. A discussion of the study findings was limited by paucity of related studies with which to compare the present study’s findings.

As compared to the FB hold, C2 and C1 holds elicited the highest activities in the right (contralateral – CL) and left (ipsilateral – IL) components of the studied muscles (erector spinae and external oblique muscles). An important observation from these findings may suggest a possible association between the most active ES muscle and the upper limb involved in infant support during the BF tasks. For instance, the CL UL offered support to the infant during the C2 hold and results revealed that activities of the CL ES muscle was marginally higher than the IL component during this BF task. Similarly, the C1 hold which involved infant support with the IL upper limb elicited marginally higher activities in the IL ES muscle, as compared to the left component. However, this trend was not observed during the FB hold which required minimum infant support with the upper limb as the infant load weight was borne by the breastfeeding pillow. These findings imply that the C2 and C1 BF holds may predispose women to breastfeeding-related musculoskeletal disorders, as compared to the FB hold. Increased trunk muscle activity contributes to muscle fatigue and may also represent a compensating mechanism for the reduced contribution of passive tissues to spinal stability [26, 27]. This further suggests that the physical stresses associated with BF can be minimized by adopting the FB hold.

In order to assess symmetry/asymmetry in the two muscle groups, this study compared activities in the CL and IL components of each muscle. Results revealed that both parts of the ES muscle were nearly activated equally during each of the BF tasks and the asymmetry ratios did not vary significantly across the three trials. However, asymmetry ratios of the EO muscles varied significantly across the BF tasks with more activity recorded in the CL components, irrespective of the BF hold adopted. Dominance in the activities of the CL EO muscle may partly be attributed to the fact that all the participants were right-handed and demonstrated dominance in the functions of the right muscles. These variability in muscle activation patterns may be explained by the postural disposition of the participants during the BF tasks. Characteristically, each BF position required a lateral twist and flexion towards the nursing breast (the left breast in this case) while the participants supported the infant with the right (CL) hand. The C1 hold position significantly elicited the least asymmetry in these muscles while the C2 hold showed more muscular asymmetries. The FB hold which practically required more trunk adjustment towards the nursing breast would have been expected to elicit higher asymmetry ratio in the lateral trunk muscles. Asymmetry in muscle activity may indicate a failure of trunk stabilization and contributes to the development of back pain and other musculoskeletal injuries [28, 29]. On a long-term basis, increased muscular activities during the C2 hold may be a possible factor of associated musculoskeletal injuries. It was also revealed that body discomforts were reported during the C2 hold BF trial as well as other holds. The C2 hold has been shown to be preferred and predominantly utilized by mothers [7, 16] and suggested to be advantageous owing to the fact that it allows for more infant head control with just one arm while the mother puts the breast in the infant’s mouth [20, 22]. Muscular asymmetries sustained over prolonged BF periods are possible factors BF-related musculoskeletal disorders. Thus, further evaluations of such muscular asymmetries are necessary on a long-term basis.

The self-reported musculoskeletal discomforts during the BF tasks showed higher prevalence of discomforts, which did not correlate with the muscle activities recorded during the task. In fact, it was not proposed that there would be a correlation among these two variables as muscle firing and recruitment does not cause pain ordinarily. Any pain or discomfort experienced from muscular activities during such tasks is probably an outcome of prolonged use, fatigue and/or other biomechanical asymmetries. Thus it is possible that the reported discomforts were temporary reactions to the BF positions adopted during the experiments. The outcomes of prolonged muscle activities during BF tasks will best be appreciated over time in a cohort study. It is necessary to educate mothers on the benefits of maintaining neutral spine postures during BF activities, irrespective of the postural requirements or characteristics of the adopted BF hold position. This can be achieved by avoiding unnecessary lateral twists, bringing the baby to the breast (rather than breast to baby), alternating the nursing breast and/or BF hold between feeding sessions to prevent adoption of prolonged postures as well as use of lumbar supports during BF. Kilinipkul et al. [15] showed that use of lumbar supports during BF reduced EMG activities of the back muscles which were further reduced by increasing thickness of the lumbar supports. Since BF durations and frequencies are usually prolonged [16], it may become necessary to consider the inclusion of mild intermittent trunk stretches and mobilizations as integral components of BF sessions, provided its limits are undisruptive of the infant’s feeding. Feeding in a semi-reclined position may pose less risk of musculoskeletal injuries to the mother as it offers more trunk support but there is need to evaluate its biomechanical characteristics in future studies.

The present study’s assessment was based on BF tasks involving the left breast only, thereby limiting its findings to considerations of the right and left muscles as contralateral and ipsilateral components, respectively. Studying from both breasts would have further explored muscular responses to the different BF holds.

6. Conclusion

FB hold elicited the least muscle activities in the most of the studied muscles while C1 hold resulted in the least asymmetry in each of the muscle groups. To determine the most biomechanically efficient of the three recommended BF positions, further longitudinal studies are necessary for a better understanding of the biomechanical changes relative to each BF hold position.