3. Conducting aerobic exercise in the heat can lead to significant and measurabl

Question

3. Conducting aerobic exercise in the heat can lead to significant and measurable body water loss. It is conceivable that up to 2 1/hr of body fluids in sweat loss may occur under these conditions. So, you pick the hottest day of the summer to see whether you can induce some significant weight loss and run three miles. Before the run, your weight was measured at 70 kg and, following the run, you measured in again at 70 kg on the same scale. Using the concepts of reliability, validity and/or sensitivity, find a way to explain the problem away as you most assuredly lost some weight during the run...and you did not consume any fluids or food along the way

Explanation / Answer

In the given case, aerobic exercise in the heat has a definite effect on the performance (especially endurance performance). Subject gets easily exhausted with increased temperature due to evaporation of water, fatigue (due to increased glycogenolysis) and less power produced from the muscles.

Since, the subject had run for three miles and no fluids have been taken along the way, there is significant water loss in the form of sweat which leads to decreased body weight. But, the scale showed, the same weight of 70 kg both initially as well as at the last even though there is significant reduction of body weight (even though minor change).

Before addressing the problem and its remedy, let us first see the definitions of Reliability, validity and/ or sensitivity:

Reliability is defined as the estimation of reproducibility of the measurement. It helps in ascertaining the degree to which the instrument (weighing scale in this case) measures the same way each time under same conditions. a. Testing and retesting and b. Internal consistency measurement helps in estimation of reliability of the instrument or procedure. Reliability should be the same with consistency across the subjects and across the measurements. Reliability coefficients are helpful for reporting the extent of reliability.

Validity refers to the efficiency of the instrument by which it truly measures the parameter which it actually claims to do. There are number of types of validity among which face validity is the most common one. Face validity indicates whether a scale measures the proposed parameter or not. Apart from face validity content validity, construct validity are also used. Content validity involves more harsh testing to establish the compliance of the equipmenet while construct validity measures the construct, the equipment is intended to measure.

Sensitivity refers to the ability of the instrument or equipment to measure and detect the smallest but clinically significant value in a process over time. It is ascertained by taking the longitudinal measures of the outcome from baseline measurement over the time.

Where the weighing scale has gone wrong?

Say for example the instrument can measure the weight in graduations of 5 kgs or 3 kgs increments, as there is nearly 2 L/ hr sweat loss (running 3 miles will approximately take 30 minutes on a slow pace). So, the final weight after exercise should be 69 kg (as the density of water is approximately 1 (0.998 gm/cc); 1 lit = lkg), since the instrument has 5 kg or 3kg increments, it can measure the difference if it is below the value of 65 or 67 respectively but anything above this value will be displayed as 70 kgs after being rounded off to the nearest integer.

Thus, the instruments lack the sensitivity, to differentiate between the initial and final values of measurements

Remedy: A sensitive balance with limit of detection less than 0.5kg (least count of 500gms) can easily quantify the significant changes in the body weight which would account for the water loss due to sweat.

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