Limitations of oxygen uptake and leg muscle activity during ascending evacuation in stairways

Reliability of stair-climbing speed in two cohorts of older adults

Background/Aims

The ability to climb stairs is an important prerequisite for activities of daily living and social participation in older adults, and is therefore an important part of rehabilitation. However, there is no consensus on how to measure stair-climbing ability. The aim of this study was to investigate the test–retest reliability of the measurement of stair-climbing speed (steps per second) as a parameter for functional ability in older adults.

Methods

A total of 57 participants who were in hospital and 56 participants who were community-dwelling and did not have any limitations in activities in daily living, all aged 60 years and over, ascended and descended a set of 13 stairs twice. The halfway point of the staircase was marked in order to split the time required for both the ascending and the descending actions. Additional measurements consisted of the Functional Reach Test, the Timed Up and Go Test, walking ability using the GAITRite walkway system and the isometric strength of four muscle groups of the lower extremities using a handheld dynamometer.

Results

Test–retest reliability of the first and second half of the stair-climbing for both ascending and descending showed excellent results for the group of hospitalised participants (intraclass correlation coefficient, [ICC] 0.87, 95% confidence interval [CI] 0.79–0.93 to 0.94, 95% CI 0.9 – 0.97 for comparison of first vs second half of stair climbing; ICC 0.9, 95% CI 0.83-0.94 to ICC 0.95, 95% CI 0.92–0.97 for comparing first vs second measurement)) and moderate to excellent results for the group of community-dwelling participants with no limitations (ICC 0.58, 95% CI 0.37–0.73 to ICC 0.76, 95% 95% CI 0.63-0.85 for comparison of first vs second half of stair climbing; ICC 0.82, 95% CI 0.71-0.89 to 0.92, 95% CI 0.87–0.95 for comparing first vs second measurement). As expected, hospitalised participants took significantly longer descending than ascending stairs (t(56)=6.98, P<0.001, d=0.93). A general and significant trend of increasing speed while descending could be observed in both groups (performing paired sample t-tests).

Conclusions

The results indicate that stair-climbing speed is not constant and that different patterns exist in older adults who have no limitations and in those who are hospitalised. The use of stair-climbing speed as an assessment tool should include both stair ascent and descent, because differences in these speeds seem to be indicators of stair-climbing ability.

Non-obstructive monitoring of muscle fatigue for low intensity dynamic exercise with infrared thermography technique

Surface electromyography (sEMG) has been widely used in evaluating muscle fatigue among athletes where electrodes are attached on the skin during the activity. Recently, infrared thermography technique (IRT) has gain popularity and shown to be another preferred method in monitoring and predicting muscle fatigue non-obstructively. This paper investigates the correlation between surface temperature and muscle activation parameters obtained using both IRT and sEMG methods simultaneously. Twenty healthy subjects were required to perform a repetitive calf raise exercise with various loads attached around their ankle for 3 min to induce fatigue on the targeted gastrocnemius muscles. Average temperature and temperature difference information were extracted from thermal images, while root mean square (RMS) and median frequency (MF) were extracted from sEMG signals. Spearman statistical analysis performed shows that there is a significant correlation between average temperature with RMS and between temperature difference with MF values at p<0.05. While ANOVA test conducted shows that there is significant impact of loads on RMS and MF where F=12.61 and 3.59, respectively, at p< 0.05. This study suggested that skin surface temperature can be utilized in monitoring and predicting muscle fatigue in low intensity dynamic exercise and can be extended to other dynamic exercises.

Walking on stairs: Experiment and model

An increasing global population forces urban planners to construct buildings and infrastructure that is extremely deep and high. Elevators and escalators serve skyscrapers and tunnels, but in an emergency people still have to walk on stairs. Computer simulations can mitigate risks of escape situations. For these situations, pedestrian locomotion models need to match reality well. Motion on stairs, however, is not nearly as well understood as motion in the plane. Publications are scarce and some are contradictory. As a result, movement on stairs is usually modeled by slowing down pedestrians by a fixed factor. But is this justified? And what happens at intermediate landings? This contribution aims to clarify inconclusive results of previous research and provide new information to directly incorporate empirical results into a parsimonious computer model. The algorithms are freely available through an open-source framework. After outlining the shortcomings of existing approaches, we present three experiments, from which we derive requirements for the computer model. Reenacting computer experiments shows the extent to which our model meets our observations. We conclude with an applied example, simulating an evacuation of Germany's famous Neuschwanstein Castle.

Oxygen uptake and muscle activity limitations during stepping on a stair machine at three different climbing speeds

This laboratory study examined human stair ascending capacity and constraining factors including legs' local muscle fatigue (LMF) and cardiorespiratory capacity. Twenty-five healthy volunteers, with mean age 35.3 years, maximal oxygen uptake (VO_2max) of 46.7 mL·min^-1·kg^-1 and maximal heart rate (HR) of 190 bpm, ascended on a stair machine at 60 and 75% (3 min each) and 90% of VO_2max (5 min or until exhaustion). The VO₂, maximal heart rate (HR_max) and electromyography (EMG) of the leg muscles were measured. The average VO_2highest reached 43.9 mL·min^-1·kg^-1, and HR_highest peaked at 185 bpm at 90% of VO_2max step rate (SR). EMG amplitudes significantly increased at all three levels, p < .05, and median frequencies decreased mostly at 90% of VO_2max SR evidencing leg LMF. Muscle activity interpretation squares were developed and effectively used to observe changes over time, confirming LMF. The combined effects of LMF and cardiorespiratory constraints reduced ascending tolerance and constrained the duration to 4.32 min. Practitioner Summary: To expedite ascending evacuation from high-rise buildings and deep underground structures, it is necessary to consider human physical load. This study investigated the limiting physiological factors and muscle activity rate changes (MARC) used in the muscle activity interpretation squares (MAIS) to evaluate leg local muscle fatigue (LMF). LMF and cardiorespiratory capacity significantly constrain human stair ascending capacities at high, constant step rates.