Upper trunk flexion versus whole trunk elevation in semi-Fowler’s position: Effects on ventilation and heart rate responses

Q: What is the clinical evidence from this study?

Study design: RCT. Population: Healthy (n=14). Intervention: Upper trunk flexion at 30° (UT30) vs. Supine position (SPIN). Primary outcome: Tidal volume (mL) (Cohen's d 1.77, p=0.0002).

Q: What does this research mean for the field?

Upper trunk flexion at 30 degrees significantly increases tidal volume compared to the supine position without significantly decreasing RR intervals in healthy young women. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

Sayuki Miyashita; Satoshi Kubota; Takuya Furudate

doi:10.2478/bhk-2026-0014

January 1, 2026Biomedical Human KineticsOpen Access

Upper trunk flexion versus whole trunk elevation in semi-Fowler’s position: Effects on ventilation and heart rate responses

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Key result

30-degree upper trunk flexion increases tidal volume ~25% vs supine without decreasing RR intervals.

Cohen's d 1.77
P=0.0002
n=14

Why the study?

Despite known cardiovascular benefits of upper trunk flexion in Fowler position, its effects in semi-Fowler position remain uninvestigated.

Does 30° upper trunk flexion improve ventilation and maintain cardiac chronotropy compared to supine and whole-trunk elevation in healthy young women?

Key Points

To compare the physiological effects of 30° upper trunk flexion versus 30° whole-trunk elevation in the semi-Fowler's position on ventilation and cardiac chronotropy.
Fourteen healthy young women (age: 20.6 ± 0.7 years, height: 162.1 ± 5.4 cm, weight: 53.1 ± 5.6 kg) participated in a randomized crossover design.
Compared supine (SPIN), 30° whole-trunk elevation (WT30), and 30° upper trunk flexion at T10 (UT30) following a 5-minute equilibration period.
Assessed tidal volume, minute ventilation, respiratory rate, and electrocardiographic RR intervals via pneumotachography and linear mixed models.
Both UT30 and WT30 significantly increased tidal volume (mean difference +78.72 mL, p = 0.0002 and +94.12 mL, p < 0.0001) and minute ventilation (mean difference +0.89 L/min, p = 0.0002 and +1.18 L/min, p < 0.0001) compared with supine, with no significant differences between UT30 and WT30.
Direct statistical comparisons of tidal volume, minute ventilation, and RR intervals between UT30 and WT30 showed no significant differences.

Study Design

Type

RCT (n=14)

Blinding

Open-label

Randomization

Randomized crossover

Multicenter

No

Structured PICO

Does 30° upper trunk flexion improve ventilation and maintain cardiac chronotropy compared to supine and whole-trunk elevation in healthy young women?

P

Population

14 healthy young women (mean age 20.6 ± 0.7 years), physically inactive, non-smokers. Excluded: respiratory or cardiovascular diseases, low back pain, and obesity.

I

Intervention

30° upper trunk flexion at T10 (UT30) for 5 minutes

C

Comparator

Supine position (SPIN) and 30° whole-trunk elevation (WT30) for 5 minutes each

O

Outcome

Tidal volume (TV), minute ventilation (MV), respiratory rate, and RR intervals after 5-min equilibrationsurrogate

Main Result

Effect estimate: Cohen's d 1.77

Absolute Event Rate: 397.06% vs 318.34%

p-value: p=0.0002

Upper trunk flexion at 30° provides similar ventilatory benefits to whole-trunk elevation but may avoid the compensatory heart rate increases seen with whole-trunk elevation.

Limitations

Sample consisted exclusively of healthy young women, limiting generalizability to men, older adults, or clinical populations
Did not directly measure abdominal muscle activity (EMG) or intra-abdominal/gastric pressures
Measured RR intervals as a surrogate for cardiac chronotropy but did not directly assess stroke volume or cardiac output
Small sample size without an a priori power analysis
Numerical Rating Scale for breathing difficulty may lack sufficient sensitivity to detect subtle differences under resting conditions
Sample consisted exclusively of healthy young women
Did not directly measure abdominal muscle activity or intra-abdominal/gastric pressures
Did not directly assess stroke volume or cardiac output
Lack of statistically significant difference in direct comparison of RRi between UT30 and WT30
Numerical Rating Scale for breathing difficulty may lack sufficient sensitivity
No a priori power analysis was conducted

Implication

May inform upright positioning to optimize ventilation; leaves open clinical utility pending validation in larger patient cohorts.

Abstract

Study aim The semi-Fowler’s position is widely used to support respiratory function and reduce cardiovascular stress. Despite the known cardiovascular benefits of upper trunk flexion in Fowler’s position, its effects in the semi-Fowler’s position remain uninvestigated. This study aimed to compare the effects of upper trunk flexion (UT30) and whole-trunk elevation (WT30) at 30° on ventilation and cardiac chronotropy in healthy young women. Material and methods Fourteen healthy young women (age: 20.6 ± 0.7 years; height: 162.1 ± 5.4 cm; weight: 53.1 ± 5.6 kg) participated in a randomized crossover design comparing supine, 30° whole-trunk elevation (WT30), and 30° upper trunk flexion at T10 (UT30). Tidal volume (TV), minute ventilation (MV), respiratory rate, and RR intervals were measured using a pneumotachograph and ECG (BIOPAC MP150) after 5-min equilibration. Data were analyzed using Linear Mixed Models (R version 4.3.3). Results Both UT30 and WT30 increased TV ( Δ + 79 and + 94 mL) and MV ( Δ + 0.89 and + 1.18 L/min) versus supine (all p < 0.001), with no UT30–WT30 differences. RR interval decreased in WT30 versus supine ( Δ − 0.029 s, ≈ +2.1 bpm, p = 0.038) but not in UT30 ( p > 0.05); the direct UT30–WT30 comparison was not significant. Conclusions These findings suggest that UT30 may be an efficient low-burden posture in healthy young women; applicability to populations with limited cardiovascular reserve requires direct clinical validation.

Discussion

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Cite This Study

Miyashita et al. (2026) conducted an RCT in Healthy (n=14). Upper trunk flexion at 30° (UT30) vs. Supine position (SPIN) was evaluated on Tidal volume (mL) (Cohen's d 1.77, p=0.0002). Upper trunk flexion at 30 degrees significantly increased tidal volume compared to the supine position without significantly decreasing RR intervals in healthy young women.

synapsesocial.com/papers/6a0021fec8f74e3340f9cfc5 https://doi.org/10.2478/bhk-2026-0014

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Upper trunk flexion versus whole trunk elevation in semi-Fowler’s position: Effects on ventilation and heart rate responses

Key Points

Study Design

Structured PICO

Main Result

Limitations

Implication

Abstract

Discussion

Cite This Study

Upper trunk flexion versus whole trunk elevation in semi-Fowler’s position: Effects on ventilation and heart rate responses

Key Points

Study Design

Structured PICO

Main Result

Limitations

Implication

Abstract

Discussion

Cite This Study

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