CASE STUDY
Examining the activity of a 6 month old infant's erector spinae muscles while in a forward-tilted seat versus a backwards-tilted seat
Examining the activity of a 6 month old baby’s erector spinae muscles while in a forward-tilted seat versus a backwards-tilted seat
Background
The erector spinae (ES) is a group of muscles and tendons which run more or less the length of the spine on the left and the right, from the sacrum or sacral region, and hips to the base of the skull. The ES is largely responsible for arching the lower back, and for proper, upright posture.1-9 Previous studies examining abdominal muscles during anterior pelvic tilting using EMG have been performed in the sitting position and have reported that the activity of the erector ES increased.4,6
Upseat Design
The Upseat was designed to incorporate a forward tilted wedge that facilitates anterior pelvic tilt. This slight forward tilt rotates the pelvis to engage the muscles responsible for proper, upright posture.
Figure 1. A depiction of the erector spinae muscles taken from Wikipedia, April 23, 2022.
Our
Hypothesis
If an infant sits in the Upseat, which features a slight forward tilt thus facilitating an anterior pelvic tilt, then they will engage their erector spinae muscles and demonstrate a more upright posture, than if they are seated in a backwards tilted seat (“the other seat”).
Our
Hypothesis
If an infant sits in the Upseat, which features a slight forward tilt thus facilitating an anterior pelvic tilt, then they will engage their erector spine muscles and demonstrate a more upright posture, than if they are seated in a backwards tilted seat (“the other seat”).
Background
The erector spinae (ES) is a group of muscles and tendons which run more or less the length of the spine on the left and the right, from the sacrum or sacral region, and hips to the base of the skull. The ES is largely responsible for arching the lower back, and for proper, upright posture.1-9 Previous studies examining abdominal muscles during anterior pelvic tilting using EMG have been performed in the sitting position and have reported that the activity of the erector ES increased.4,6
Figure 1. A depiction of the erector spinae muscles taken from Wikipedia, April 23, 2022.
Upseat Design
The Upseat was designed to incorporate a forward tilted wedge that facilitates anterior pelvic tilt. This slight forward tilt rotates the pelvis to engage the muscles responsible for proper, upright posture.
Our
Hypothesis
If an infant sits in the Upseat, which features a slight forward tilt thus facilitating an anterior pelvic tilt, then they will engage their erector spine muscles and demonstrate a more upright posture, than if they are seated in a backwards tilted seat (“the other seat”).
Our
Hypothesis
If an infant sits in the Upseat, which features a slight forward tilt thus facilitating an anterior pelvic tilt, then they will engage their erector spine muscles and demonstrate a more upright posture, than if they are seated in a backwards tilted seat (“the other seat”).
Study Design
In this study we used surface electromyography (EMG equipment; sEMG) to measure the muscle activity in the erector spinae muscles of a six and a half month old infant. sEMG was measured when the infant was sitting in a slightly forward-tilted seat (the Upseat), and then in a backwards-tilted seat (“the other seat”). The Myonyx 2-Channel Surface EMG and Biograph Infiniti software was used to measure and compare the muscle activity while in the two different seats. Two electrodes were placed over the infant's erector spinae muscles and the control electrode was placed on the infant's iliac crest. We took sEMG measurements/readings in both seats while the infant was in a similar state of calmness. Due to the fact that an infant's overall state (i.e. happy or crying, sitting still or struggling to reach for an object) is temperamental and very difficult to predict or control, we transitioned the infant from one seat to the other every two to four minutes, and repeated the process until we had a fair side-by-side sEMG reading of the infant in a calm state.
The area occupied by the EMG signal for a set period of time (20-30 seconds) was generated using the Biograph Infiniti software, and was used to approximate the muscle activity in each of the seats. The areas generated for each of the two seats was then compared.
We also observed the posture of the infants in each of the seats, and rated the posture as slouched, neutral, or upright.
Figure 2. Surface EMG electrodes were placed over the left erector spinae muscles of an infant that was approximately six and a half months old. A control elected was placed over the babies left ileum.
Results
Figure 3. Surface EMG measurements demonstrated that the erector spinae muscles were noticeably more active when the infant was sitting in the forward-tilted Upseat (shown here at 2:15s-2:39s) than in the other backwards-tilted seat (shown here at 2:40s-3:05s).
Upseat 2:15s — 2:39s
| Minimum | Maximum | Max. (-) Min | Average | Standard Deviation | Variability | Area | |
|
EMG |
-641.56 |
716.30 |
1357.85 |
-0.01 |
66.14 |
-8337.19 |
1107.41 |
|
Medium Frequency |
25.00 |
49.00 |
24.00 |
36.83 |
5.38 |
0.15 |
899.84 |
Other Seats 2:41s — 3:05s
| Minimum | Maximum | Max. (-) Min | Average | Standard Deviation | Variability | Area | |
|
EMG |
-160.68 |
224.34 |
385.02 |
0.00 |
32.62 |
10945.37 |
552.92 |
|
Medium Frequency |
28.00 |
66.00 |
38.00 |
39.17 |
6.85 |
0.17 |
918.03 |
Upseat Area vs. Other Seat Area
| Area |
|
2.00 |
Table 1. A comparison of the clean side-by-side EMG measurements take for the first 24 seconds of the infant in the forward-tilted seat (Upseat) vs the first 24 seconds of the infant in the backwards-tilted seat (the other seat). The area of the plotted graph was taken to be an approximation of muscle activity. During this session, it can be seen that the infant's erector spinae muscles (responsible for proper, upright posture) were 2x more active while in the forward-tilted Upseat, than while in the backwards-tilted seat.
Figure 4. Surface EMG electrodes were placed over the left erector spinae muscles of an infant that was approximately six and a half months old. A control elected was placed over the infant's left ileum.
Figure 5. A six and a half month infant sitting in a backwards-titled seat, clearly in a slouched position.
Discussion
A period of 48 seconds was selected for this study, as this was the maximum duration of time in which the infant was in a state of calmness. Calmness was equated to the infant being in a neutral sitting position (i.e. not leaning over) and displaying emotions of interest/contentless (i.e. not fussing/crying or showing emotions of discomfort). We endeavoured to maintain the same calmness with the infant by presenting them with equally novel stimuli that extracted the same level of engagement. Of the 48 seconds, the first 24 seconds was when the infant was in the forward-tilted Upseat, and the last 24 seconds was when the infant was in the backwards-tilted other seat.
The area that was measured using the Biograph Infiniti software suggested that the infant’s erector spinae muscles were 2x more active in the forward-tilted Upseat than in the backwards-tilted other seat (Table 1). Specifically, the EMG reading for the area of the forward-tilted Upseat was 1107.41 compared to 552.92 measured for the backwards-tilted seat. This is consistent with the infant’s upright posture in the forward-tilted Upseat (Figure 4) and the infant’s slouched position in the backwards-tilted seat (Figure 5). These findings are also consistent with previous studies which demonstrated that an anterior pelvic tilt seating position engages the erector spinae muscles, and encourages upright posture.4, 6
The infant remained in each of the two seats for at least 2:39 seconds (2:39s in total for the forward-tilted Upseat and slightly longer while in the backwards-tilted seat). The 48 second period of time that was selected for a fair/equivalent comparison of muscle activity in the two seats showed the erector spinae muscles to be noticeably more active when the infant was sitting in the forward-tilted Upseat.
Conclusion
Therefore, because the Upseat’s ergonomic design encourages anterior pelvic tilt, an infant’s erector spinae muscles are 2x more engaged than when they are placed in a backwards tilted seat. This is due to the Upseat’s patented design, forward titled wedge incorporated into the base of the seat.
References
- Phys Ther Res. 2016; 19(1): 50–57. Published online 2016 Nov 29. PMCID: PMC5342962. PMID: 28289581 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5342962/
- Day JW, Smidt GL and Lehmann T: Effect of Pelvic Tilt on Standing Posture. Phys Ther. 1984, 64: 510-516.
- Levine D and Whittle MW: The effects of pelvic movement on lumbar lordosis in the standing position. J Orthop Sports Phys Ther. 1996, 24: 130-135.
- Floyd WF and Silver PH: The function of the erectores spinae muscles in certain movements and postures in man. J Physiol. 1955, 129: 184-203. Note: This article demonstrates that activity of the ES (responsible for arching the lower back) is increased when the subject is sitting upright.
- Blackburn S and Portney L: Electromyographic Activity of Back Musculature During Williams' Flexion Exercises. Phys Ther. 1981, 61: 878-885.
- Andersson BJ, Jonsson B and Ortengren R: Myoelectric activity in individual lumbar erector spinae muscles in sitting. A study with surface and wire electrodes. Scand J Rehabil Med Suppl. 1974, 3: 91-108.
- Walters CE and Partridge MJ: Electromyographic study of the differential action of the abdominal muscles during exercise. Am J Phys Med. 1957, 36: 259-268.
- Partridge MJ and Walters CE: Participation of the abdominal muscles in various movements of the trunk in man: an electromyographic study. Phys Ther Rev. 1959, 39: 791-800.
- Richardson C, Jull G, Toppenberg R and Comerford M: Techniques for active lumbar stabilisation for spinal protection: a pilot study. Aust J Physiother. 1992, 38: 105-112.
