Variability in estimated METs

Ainsworth, et al. (1993) have compiled an extensive compendium on the estimated MET values for a variety of physical activities. It is important to recognise that these values are estimates, which means that each individual patient could be working above or below this estimate. The variability of the estimate depends on the simplicity or complexity of the movements. For example, the variability of pedalling an exercise cycle ergometer will likely be less than that of stepping or walking. The motor skill involved in cycle ergometry is fixed by the motion of the pedal crank and mainly involves the legs. Stepping and walking require the individual to balance and use arm and trunk motions, which can vary much more than cycling.

In cardiac rehabilitation, the MET values from the patients' exercise ECG stress test are typically reported. These data provide the exercise leader with information of both intensity and functional capacity. It should be noted, if the ETT is carried out using a motorised treadmill, how much the MET value can be altered by the patient holding on to the handrail. Astrand (1982) reported that when walking on the treadmill with hands on the rail, the VO2 was as much as 9ml.kg-1.min-1 (2.6 METs) lower than walking with hands free. Most patients attending an exercise ECG stress test will hold on to the rail because they are typically unfamiliar with treadmill exercise and are not used to a moving platform. In addition treadmill walking mechanics are very different from floor walking, making direct comparison of floor to treadmill walking questionable.

Using the ACSM (2000) equations or data from Ainsworth, et al. (1993), MET values can also be estimated from submaximal protocols recommended for assessing functional capacity in cardiac patients in the UK, including: step tests, shuttle walks and cycle ergometry (BACR, 1995; Tobin and Thow, 1999; ACPICR, 2003; Fowler, et al., 2005).

For box-stepping exercise performed in healthy young individuals, the variability (based on the 95% limits of agreement) in the estimated versus actual MET (VO2) values was found to be up to 1.3 METs (4.5ml.kg-1.min-1) (Buckley, et al., 2004). This work on box stepping is presently being replicated by Buckley with older individuals and cardiovascular patients as participants. It is anticipated that such variability would not be less than that found in the younger, healthier and more active individuals reported above. Another step test being suggested for rehabilitation settings is the Chester step test (CST) (Sykes, 1995). The CST is a sub-max, multi-stage test lasting for 10 minutes with a choice of four step heights. It has been shown to be valid in the estimation of aerobic capacity in a non-clinical sample with a range of fitness levels (Sykes and Roberts, 2004). This novel test would appear to be promising in the CR setting. The estimated MET values for step heights and stepping rates that would be appropriate to cardiac populations are summarised in Table 3.6.

The assessment recommended by Tobin and Thow (1999) and SIGN (2002), which is adapted from Singh, et al. (1992), provides walking speeds for each

Table 3.6. Estimated metabolic equivalents (METs) for box stepping on a 6-inch,

8-inch and 10-inch step

*Stepping rate **Metronome METs for a METs for an METs for a (steps-min-1) setting (beats-min-1) 6-inch step 8-inch step 10-inch step

Table 3.6. Estimated metabolic equivalents (METs) for box stepping on a 6-inch,

8-inch and 10-inch step

*Stepping rate **Metronome METs for a METs for an METs for a (steps-min-1) setting (beats-min-1) 6-inch step 8-inch step 10-inch step

14

56

2.8

3.4

3.9

16

64

3.2

3.8

4.4

18

72

3.6

4.3

5.0

20

80

4

4.8

5.5

22

88

4.4

5.3

6.1

24

96

4.8

5.8

6.6

26

104

5.2

6.2

7.2

28

112

5.6

6.7

7.7

30

120

6

7.2

8.3

* One step, commencing from both feet on the ground, constitutes each foot stepping up and then each foot stepping down. Each foot movement is paced with each beat of the ** Metronome; four beats of the metronome equal a one-step cycle. (Adapted from the ACSM, 2000, p. 305.)

* One step, commencing from both feet on the ground, constitutes each foot stepping up and then each foot stepping down. Each foot movement is paced with each beat of the ** Metronome; four beats of the metronome equal a one-step cycle. (Adapted from the ACSM, 2000, p. 305.)

testing stage, which can be converted into METs. An important point to remember is that the testing stages are only one minute in duration, which means that it is more difficult to determine the MET level that an individual can actually sustain. Furthermore, in each of these one-minute periods, the heart rate and RPE responses will not have had time to plateau, to associate the MET level with the corresponding HR or RPE. Box 3.1 provides the shuttle walk test protocol (SIGN, 2002).

Box 3.1 Shuttle walk test protocol

Run for Your Life The Health Benefits Of Treadmills

Run for Your Life The Health Benefits Of Treadmills

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