Dear Preetam Nath,

the NAFLD is also a interesting group we are currently studying.

The best option to assess changes in metabolic function and fitness would be an intervention study that measures physical fitness (VO2max) and VT1 (ventilatory threshold) by spiroergometry at study entry and end. Indirect spiroergometry will also enable you to assess increases in fat utilisation at a given exercise intensity.

However, studying adherence to your exercise intervention is the major obstacle to solve. Compliance does not seem to be too high, if you go for measuring tools like pedometers, heart rate monitors or accelerometry. Accordingly self-reported questionnairs are still inevitable. Might be worth while to assess the IPAQ every 7 days:

http://www.sdp.univ.fvg.it/sites/default/files/IPAQ_English_self-admin_long.pdf

If you come accross a better solution, please let me know.

Perikles

Dear Preetam Nath,

A metabolic and physical performance measure such as VO2max would certainly assess physical fitness.  Measuring physical activity becomes far more difficult than measuring physical fitness as behaviour and lifestyle choices can heavily influence the level of activity reflective of daily life rather than exercise capacity.  The wear time and compliance of physical activity monitoring (as Perikles states) can be a particular problem for data capture in research trials.  We have collected data in the chronic respiratory population using metabolic accelerometers know as SenseWear devices.  These monitors provide variables in METs (intensity is qualified accordingly), TEE and steps.  Unfortunately, and as I understand it, these are no longer in production but they may still be available through other distributers.  Otherwise there are other well validated accelerometers such as those available through Actigraph (GT3x etc.,) but these do not have the ability to directly measure metabolic intensity during physical activity.  I would also suggest using an accompanying questionnaire such as the IPAQ to capture additional data to that attained though objective monitoring.

Be good to hear how you decide to progress with your trial.

Theresa

Dear Preetam Nath,

I've had a very good experience using Actigraph GT3X to measure habitual physical activity in older adults, and the measurements showed a good relaionship with VO2 peak measured directly during an incremental shuttle exercise testing. Also, I have had no problems with compliance using the GT3X device, and it's very simple to manage.

Best Regards,

Alessandra.

Dear Preetam Nath,

The most precise measure of intensity is oxygen consumption (VO2). VO2 represents the overall metabolic challenge that an exercise imposes. There is a direct linear relationship between intensity of aerobic exercise and VO2. Our maximum intensity is a reflection of our maximal oxygen consumption (VO2 max). Such a measurement represents a cardiovascular fitness level.[3]

VO2 is measured in METs (mL/kg/min). One MET, which is equal to 3.5 ml/kg per minute, is considered to be the average resting energy expenditure of a typical human being. Intensity of exercise can be expressed as multiples of resting energy expenditure. An intensity of exercise equivalent to 6 METs means that the energy expenditure of the exercise is six times the resting energy expenditure.[4]

Intensity of exercise can be expressed in absolute or relative terms. For example, two individuals with different measures of VO2 max, running at 7 mph are running at the same absolute intensity (miles/hour) but a different relative intensity (% of VO2 max expended). The individual with the higher VO2 max is running at a lower intensity at this pace than the individual with the lower VO2 max is.[5]

Some studies measure exercise intensity by having subjects perform exercise trials to determine peak power output,[6] which may be measured in watts, heart rate, or (on a cycle) average cadence (cycling). This approach attempts to gauge overall workload.

Dear Preetam Nath,

Assuming you are interested in the intensity of continuous aerobic exercise, accurately measuring intensity in the laboratory is best done by first conducting a graded maximal exercise test using heart rate monitoring and spiroergometry. If the test does not need to be stopped prematurely, e.g. due to the appearance of cardiac symptoms, you will have data on VO2peak (usually not VO2max in clinical populations), and maximum heart rate (HRmax), as well as maximum work rate (WRpeak) if using a cycle ergometer for example. You then have a few ways to track intensity during exercise: 1) gas exchange measurement if available; 2) heart rate; and 3) work rate depending on the type of exercise. I.e. you can calculate %VO2peak, %HRmax, and/or %WRmax. HR is in many ways the best measure as HRmax does not change with fitness whereas VO2peak and WRmax will go up with increasing fitness. Further, HR monitors are relatively inexpensive.

Please note that HR monitoring does not work well for high-intensity intermittent training or other intermittent exercise scenarios as it takes time for HR to catch up to effort. Although more subjective, I would recommend a 6-20 Rating of Perceived Exertion 'Borg' scale to set goal intensity in this scenario. However, average HR per session could still be used as an objective measure.

For assessing intensity for resistance training, convention is to establish a one repetition maximum for each exercise and calculate intensity from their. I would argue that this isn't the safest or even most accurate option for clinical and/or untrained populations who are unaccustomed to maximal efforts. You can always use a 5 repetition maximum, or even a higher number of repetitions. The problem is that you will need to retest as strength increases if this measure is very important to you.

The gas exchange data from spiroergometry can used to assess energy expenditure. It seems unlikely that you would be able to use the required equipment for multiple exercise sessions, so you may need to derive estimates of energy expenditure from HR, or use and accelerometer. The latter however is not a good option for relatively stationary activities such as stationary cycle or resistance exercise.

Accelerometers, like the GeneActiv can be useful to track overall activity. The accuracy is improved by analysing the data with an algorithm validated in your sample population.

The reference standard for real-world tracking of energy expenditure (total not just exercise related) is doubly labelled water. This is an expensive option, so it depends on your budget and sample size, as well as how important this measure is.

Good luck,

Christian