Author Identifier

Toni Haddad

http://orcid.org/0000-0002-3231-5272

Date of Award

2024

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Medical and Health Sciences

First Supervisor

Chris Abbiss

Second Supervisor

Gregory Blain

Third Supervisor

Jeanick Brisswalter

Abstract

Around the world, life expectancy is increasing, the ageing population is growing, and maintaining quality of life at an older age currently represents a major global challenge. While ‘successful ageing’ relies on a variety of factors, aerobic performance and exercise capacity are key determinants and attenuating their decline is of the utmost importance. The decrease in maximal oxygen consumption is often considered as a major determinant explaining the age[1]related decline in aerobic performance. Yet, multiple physiological systems are impaired with ageing and their contribution to aerobic limitation in older individuals is unclear. Understanding how the limitations to aerobic performance may change with ageing is an important step that will help better identify the specific needs of an older population and provide more targeted advice and guidance. Thus, the primary purpose of the three research studies contained within this doctoral thesis was to characterise the effects of ageing on the pulmonary and cardio-vascular limitations to aerobic performance. A second purpose of this thesis was to use non-invasive methods, easy to implement, to assess such limitations in older participants (i.e., > 60 y).

The first study (Study 1) aimed at better understanding the contribution of the pulmonary function (i.e., mechanical ventilatory capacity) to aerobic performance in older population (i.e., > 60 y). Fourteen endurance-trained older men (68 ± 6 y) completed two 5-km cycling time trials while breathing room air (i.e., 21% O2–79% N2) or a low-density gas (i.e., Heliox, 21% O2–79% He). Heliox was chosen for its potential to reduce airways resistance, counterbalance the age-related increase in the resistive work of breathing and blunt the expiratory flow limitation often observed with ageing. Exercise performance improved with Heliox (average power output increased by 1.8 ± 2.4%, P = 0.017; performance time decreased by 0.7 ± 0.9%, P = 0.011) and respiratory muscle force development was reduced during both inspiration (− 22.8 ± 11.6%, P < 0.001) and expiration (− 10.8 ± 11.4%, P = 0.003) compared with room air. The small improvement in exercise performance observed with Heliox suggests that the contribution of pulmonary mechanical resistance on aerobic performance is somewhat limited although it can be meaningful in competitive older-trained athletes.

After investigating the role of pulmonary function in the first study, the following two studies aimed at better understanding the contribution of cardio-vascular and vascular-oxidative functions to aerobic performance in older individuals. Study 2 assessed whether reducing active muscle mass during exercise may have a similar effect on exercise capacity in both older (i.e., > 60 y) and younger r (i.e., < 40 y) individuals. Aerobic performance during large muscle mass exercise appears to be primarily limited by central factors (i.e., oxygen delivery) while peripheral factors (i.e., oxygen utilisation) are considered to represent the main aerobic limitation to small muscle mass exercise. Single-leg cycling was therefore compared with double-leg cycling in older vs younger individuals since it may indirectly inform whether the limitations to aerobic exercise are different with ageing. 16 older (67±5 y) and 14 younger (35±5 y) individuals performed maximal self-paced single-leg and double-leg cycling efforts. Power output per leg was determined during single- and double-leg cycling and compared, as a ratio (RatioPower SL/DL), between the two groups. Power output per leg was greater during single-leg compared with double-leg cycling in both groups, and the RatioPower SL/DLwas greater in older compared with younger individuals (1.14 vs. 1.06, P = 0.041). A positive and significant relationship was observed between the RatioPower SL/DL and markers of fitness status such as V̇ O2max (r = 0.886, P < 0.001, n = 14) and peak power output relative to body mass (r = 0.854, P < 0.001, n = 14) in the younger but not in the older subgroup. These results indicate that reducing active muscle mass increased exercise capacity to a greater extent in older compared with younger individuals and suggests an age-related change in the contribution of central cardio-vascular and peripheral vascular-oxidative function to exercise performance.

Study 3 further investigated the possible mechanisms explaining the greater exercise performance observed when reducing active muscle mass in Study 2. Specifically, the functional changes in leg blood flow and oxygen peripheral utilisation were assessed in response to single-leg and double-leg cycling to better understand the contribution of vascular function and peripheral oxidative function to exercise performance. Femoral blood flow was assessed using Doppler ultrasound and vastus lateralis oxygenation was measured using near-infrared spectrometry in 12 older (65 ± 4 y) and 12 younger (35 ± 5 y) endurance-trained individuals and compared between exercise modalities and age groups. Irrespective of age, an 11% greater power output (295 ± 83 vs. 265 ± 70 W, P < 0.001) was observed during single-leg compared with double-leg cycling and was accompanied by a ~31% greater peak femoral blood flow (1749.1 ± 533.3 vs. 1329.7 ± 391.7 ml/min, P < 0.001). Peak blood flow was lower in older compared with younger athletes (1355.4 ± 385.8 vs 1765.2 ± 559.6 ml/min, P = 0.019) while muscle deoxygenation was not significantly different, irrespective of exercise modality. Peak blood flow was correlated with power output during single-leg (r = 0.655, P = 0.002) and double-leg (r = 0.666, P = 0.001) cycling. These results support the finding that a transition 8 from large to small muscle mass exercise may allow for a greater peripheral hyperaemic response which may in turn increase oxygen delivery and aerobic performance. While oxygen peripheral utilisation was similar between older and younger trained individuals and could be preserved with ageing, blood flow was consistently lower in the older group indicating some vascular impairment despite regular participation in physical activity.

In conclusion, the general findings of this thesis indicate that the contribution of pulmonary and cardio-vascular functions to aerobic performance may differ between younger and older individuals. Unloading the respiratory muscles slightly improved exercise performance in older trained athletes, indicating that the age-related impairment in pulmonary function may play a role in aerobic limitation. Reducing active muscle mass exercise increased exercise performance to a greater extent in older compared with younger individuals, suggesting a greater decrease in central oxygen delivery compared with peripheral oxygen utilisation with ageing. Manipulating respiratory muscle load and active muscle during exercise represent practical promising models that allow to better understand the pulmonary, cardio-vascular and vascular-oxidative limitations to aerobic performance. Such models may help coaches, scientists, and medical professionals when designing specific interventions to promote exercise performance, health, and autonomy in an ageing population.

DOI

10.25958/j5wt-bn80

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