[Efficiency as a new parameter of physical fitness of patients in 6-minute-walk-test]

AIMS OF THE INVESTIGATION: The 6-minute-walk-test (6-MWT) is an effective tool for measuring physical fitness in elderly patients. The increased walking distance is taken as a parameter for improved physical conditions. Frequently an unaltered walking distance is found after participation in a rehabilitation measure, but heart rate is significantly lower in the second challenge, indicating an improved physical fitness. This positive effect is not recognized when only the walking distance is considered.

We therefore carried out a retrospective analysis of the 6-MWT tests performed by 303 male patients (69.2 ± 8.7 years) before and after 3-4 weeks of clinical rehabilitation. Instrumented by a mobile pulse oximeter for recording oxygen saturation and heart rate, patients were instructed at the outset and at the end of their rehabilitation stay to walk as fast as they could during 6 min. Measurements were performed every 30 s and printed. A new parameter, efficiency (E = S/6/f (C)) was introduced: the ratio of the walking distance, S, divided by 6 min and divided by the mean heart frequency, f (C) (beats/minute).

The patients group walked 351 ± 79 m at 106.2 ± 12.7 beats/min in the initial 6-MWT and 362 ± 76.0 m at a heart rate of 104.0 ± 12.2 beats/min in the final test. Along with the increase in walking distance, efficiency E increased from 0.56 ± 0.13 m/beat to 0.59 ± 0.12 m/beat. Efficiency significantly correlates with the walking distance (p < 0.01). 54 patients (18%) had an increased efficiency in the final test at the end of rehabilitation although they walked a shorter distance compared to the initial test value: they walked with a lower heart frequency.

The patient's performance of the second walk test with an unchanged distance at a lower heart frequency reveals an improved physical fitness. This is solely described by an increase of the parameter of efficiency, E. Calculation of this parameter delivers a quantification of the effect of exercise training irrespective of the patient's cooperation. Efficiency, hence, is a meaningful complement to the sole consideration of the distance walked in the assessment of physical fitness as a benefit of rehabilitation.