On the International Space Station, astronauts undergo health assessments beginning flight day 14 and continuing every 30 days until completion of the mission. Fitness is also assessed prior to space walks. The existing process for evaluating astronaut fitness in space requires a number of tests. However, new technologies using near infrared spectroscopy (NIRS) to determine muscle oxygenation and pH may provide a simple and straightforward measure of aerobic capacity and muscle strength. In this project, Dr. Babs R. Soller and co-investigator Dr. R. Donald Hagan are evaluating a new NIRS monitoring device’s ability to measure muscle metabolism during the NASA exercise protocols used to assess fitness before, during and after flights.
Overview
Development and Testing of a Noninvasive Sensor for Measurement of Muscle Metabolism During Exercise
Principal Investigator:
Babs R. Soller, Ph.D.
Organization:
University of Massachusetts Medical School
Technical Summary
Physical exercise is the most important countermeasure currently used on the International Space Station (ISS) to mitigate muscle atrophy and bone loss, and to maintain cardiopulmonary function capacity. On ISS, assessment of health status is determined from a Periodic Fitness Evaluation (PFE) conducted starting on flight day 14 and every 30 days thereafter until the completion of the missions.
This medical requirement is described in document MR080L, Cardiovascular Physical Fitness Evaluation: Cycle Ergometry. Another medical requirement is certification for extravehicular activity (EVA). This test is conducted two weeks prior to a scheduled EVA. The test using arm cycle ergometry is described in document MR038L. In both tests, heart rate response in relation to ergometer workload is used to assess physical work capacity. However, the PFE calls for the measurement of oxygen uptake to assess aerobic capacity.
Presently, the requirement for metabolism gas analysis is waived due to limitations of the equipment. However, new technologies using near infrared spectroscopy (NIRS) to determine muscle oxygenation levels may provide a simple and straightforward measure of aerobic capacity. Thus, the goal of this project is to evaluate a new NIRS monitoring device for the assessment of crew health and performance capacities.
Near infrared spectroscopy (NIRS) can be used to simultaneously and continuously measure tissue oxygenation parameters, including muscle oxygen tension (PO2) and muscle pH. These parameters can be measured noninvasively on specific muscles to continually assess muscle metabolism during exercise. Previous studies indicate that oxygen consumption, which is traditionally measured with a metabolic gas analyzer, can be calculated from near infrared spectra. This project will investigate the relationship between whole-body oxygen uptake and local tissue muscle oxygenation. The findings may allow reassessment of the need for metabolic gas analysis during the periodic fitness evaluation and the use of heart rate during arm ergometry testing for certification of EVA. The device might also provide a quantitative assessment of pre-EVA hand-grip strength (MR081L, Physical Fitness Evaluation: Handgrip Dynamometry) where no metric currently exists.
The first NIRS sensor that was developed was used to study muscle oxygenation responses during exhaustive rhythmic handgrip dynamometry exercise. Preliminary evaluation of on-going data collection suggests that the exercise protocol that we are using may not be sensitive enough to detect changes in muscle oxygenation patterns between endurance and strength-trained athletes.
Earth Applications
The metabolic sensor developed as part of this project and our other NSBRI project (Noninvasive Measurement of Blood and Tissue Chemistry) as Earth applications in critical care medicine, exercise physiology, sports medicine and rehabilitation. This Space Medicine Project is aimed at the last three applications. Both aerobic fitness and muscle strength are lost during long periods of immobility, whether they be in space or as a result of bed-confining illness. The sensors developed in this project are expected to be able to noninvasively assess loss of fitness and improvement in strength and aerobic capacity as a result of training or rehabilitation.
The regular measurement of lactate threshold is a very common training technique for high-performance as well as weekend athletes. The noninvasive measurement of muscle pH as a surrogate for measuring lactate with a blood sample would revolutionize training by allowing continuous, noninvasive measurement throughout exercise.
This project's funding ended in 2006