Influence of inspiratory resistance on performance during graded exercise tests on a cycle ergometer
Introduction
The increasing risks of chemical hazards can be minimised by using respiratory protective devices such as gasmasks with improved canisters. A disadvantage of the use of protection means is the introduced inspiratory resistance, varying from about 0.5 kPa s l−1 (Sulotto et al., 1993) till over 1.0 kPa s l−1 (Amis et al., 2000). Open air breathing on the contrary showed an average inspiratory resistance of 0.02 kPa s·l−1 (Dressendorfer et al., 1977). However, the literature provides no clear insight in the effects of breathing (inspiratory) resistance on physical performance (see for a review: Heus et al., 1997).
To reduce the extra physical load due to inspiratory resistance, other ways of respiratory protection are studied e.g. positive pressure breathing (van de Water and Wammes, 1998; den Hartog et al., 2003), but with the present technology it is still impossible to use these new developments in combat circumstances. So, at present and in the near future, soldiers and (VN) weapon inspectors have to work with traditional gasmasks and canisters.
A first study was performed to investigate the breathing resistance of an industrial canister connected with a hose to the gasmask (Heus, 1998). In this study no differences in physiological parameters and total exercise time at a fixed work load were found between the use of the new canister with hose and the traditional military canister placed directly on the mask. In the current study a wider range of inspiratory resistance levels has been chosen.
An open question is if increased inspiratory resistance will lead to a decreased work capacity at all. Current questions are: is there a threshold in inspiratory resistance above which normal work can no longer be done, what is the relation between inspiratory resistance and loss of performance and more specifically, what is the effect of inspiratory resistance on maximal performance and time to exhaustion.
It was hypothesised that increasing levels of inspiratory resistance lead to a gradual reduction in performance time on a graded exercise test (GXT) and increased VO2-max due to the involvement of the respiratory muscles.
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Subjects
Nine male subjects (Table 1) participated in this study, which was approved by the ethical committee of TNO Human Factors. After clear instructions, subjects signed an informed consent to participate in the experiments.
Protocol
All subjects carried out a maximum performance test (GXT) on a bicycle ergometer (Lode Excalibur, Groningen the Netherlands) under supervision of two experimenters. The protocol, developed by the Netherlands Sports Medical Consultancy, is known as the SMA-protocol and is
Oxygen uptake
The VO2 was lower during the “no resistance” condition (Fig. 2). This difference was significant for all work stages, but not for all conditions in the same way. The mean VO2 (1780 ml min−1) during the complete “no resistance” condition was lower than the other conditions (low, medium and high: 2416 ml min−1, 2244 ml min−1 and 1920 ml min−1 respectively).
The slope of the VO2-curves in Fig. 2 showed an increase with increasing inspiratory resistance. The slopes were respectively 2.1, 2.8, 3.3 and 4.4 (VO
Discussion
This study shows that inspiratory resistance limits physical performance. The levels of inspiratory resistance used in this study exceed accepted levels of inspiratory resistance mentioned in literature (Bentley et al., 1973; Cotes, 1979; Deno et al., 1981; Sulotto et al., 1993; Amis et al., 2000), but the resistance is strongly dependent on the flow used (Heus et al., 1997). The higher the flow the higher the resistance and most of the standardised values were based on static flows instead of
Conclusions
This study showed that inspiratory resistance has an influence on the physical performance and thus hinders the users of respiratory protective devices in doing heavy (physical) duties. The main conclusions are:
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The workload in terms of oxygen uptake with any inspiratory resistance is higher compared to situations without inspiratory resistance.
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Oxygen uptake did not differ significantly between the different levels of inspiratory resistance.
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VO2-max increased with increasing inspiratory
Acknowledgements
This study was funded by: The Royal Netherlands Army, KPU Department, PO Box 3003, NL3800DA Amersfoort, the Netherlands.
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