Singla-Richa modified shuttle walk test

Here, the basic protocol of exercise was same as that of CSWT,[2] but the audio signal had been modified (CD available). We used an audio signal with reverse number counting being played on a music system (mobile phone). This audio signal had been calibrated according to the seconds left during each shuttle period. If there was shuttle of 20 s, the audio signal would be playing 20, 19, 18, 17 and so on up to 1 at a constant interval. If there was shuttle of 15 s, the audio signal would be playing 15, 14, 13, 12, and so on up to 1. This would guide the test subject while walking so that the test subject would know how much time was left to complete each shuttle. This would help the subject to adjust speed to complete the shuttle on time as per protocol preventing him/her to reach the end of the shuttle distance too early or too late. Furthermore at the beginning of each next level, the audio signal announced the number of shuttles to be performed in that level again attempting to understand and perform the test better.

In both type of tests, CSWT as well as in SWT_SR, the subject was instructed, “Walk or may be run, if required, at a steady pace, aiming to turn around when you hear the audio signal in the form of a bleep or end of a count depending upon the test. You should continue to walk until you feel that you are unable to maintain the required speed, without becoming unduly breathless or fatigue and/or when instructed to stop.”

The test was to be terminated by either (a) the patient, when he or she was too breathless to maintain the required speed or (b) the operator, if the patient failed to complete a shuttle in the time allowed (that is, was more than 0.5 m away from the cone when the audio signal sounded).

After performing both the tests, the subjects were asked to fill a questionnaire about the tests, and their perceptions (strongly disagree/disagree/not able to decide/agree/strongly agree) were evaluated by Likert scale. The questionnaire was, “It was easy to complete the test using reverse counting test (SWT_SR).”

We analyzed the data using Stata version 13.2 (StataCorp, College Station, TX, USA) and MedCalc 12.7 (MedCalc Software, Belgium). Proportions and means (standard deviation [SD]) were calculated for categorical and continuous variables respectively. Scatter plot was drawn between distance walked by CSWT and SWT_SR. Correlations between CSWT and SWT_SR tests were performed to verify criterion validity, using the criterion of r - 0.7 as a validity marker.[12] The Bland–Altman plot was plotted to compare CSWT and SWT_SR. In this graphical method, the differences of both methods was plotted against the reference method, that is, CSWT.[13] To assess test-retest reliability we considered repeated responses within a participant as longitudinal data and computed the intraclass correlation coefficient (ICC) based on a mixed-effects linear model, classifying the values as low (ICC: <0.4), good (ICC: 0.4–0.75), and excellent (ICC: >0.75). We also quantified reliability as the canonical correlation between the two sets of repeated measurements. For internal consistency Cronbach's alpha, a function of the average covariance (or correlation) among all possible combinations of the variable was measured. The acceptability of the SWT_SR was assessed by response to the questionnaires on 5 point Likert scale.