Activity-based pacing: comparison of a device using an accelerometer versus a piezoelectric crystal.

The EXCEL VR, an accelerometer-based pacemaker (AC), and the Legend, a pacemaker utilizing a piezoelectric crystal (PZ), were compared under ergometric conditions and during stair climbing to assess the appropriateness of their rate responses. The pacemakers, programmed to the manufacturers' nominal settings in order to compare different technologically based sensors under identical conditions, were strapped over subjects' left mid-pectoral region. Placement of the devices was randomized to control for positional effects. Ten healthy subjects (55-72 years) completed a graded exercise treadmill test to 80% of maximum predicted heart rate (HR). An additional group of ten subjects (50-66 years) completed exercise protocols involving bicycle ergometry and stair climbing. Throughout all tests, pacemaker pulse rates and subjects' intrinsic HR were monitored continuously. For the treadmill exercise, the average correlations between the AC and PZ pacemakers' pulse rate and HR for the group as a whole were r = 0.92 and r = 0.82, respectively. Individual subject comparisons were also made between each pacemaker rate and intrinsic HR. The mean difference from intrinsic rate was 11 ppm for the AC pacemaker and 24 ppm for the PZ pacemaker. In addition, the PZ pacemaker's maximal pulse rate was significantly lower (105 +/- 9.6 ppm) than the other two rates (AC 137 +/- 6 ppm; intrinsic HR 129 +/- 2 beats/min). Throughout the bicycle ergometry testing, the intrinsic HR was higher than the AC and PZ pacing rates. However, the AC's rate was significantly higher than the PZ's rate. When subjects ascended stairs, the intrinsic HR and AC rate were closely correlated, but the PZ rate was significantly lower.(ABSTRACT TRUNCATED AT 250 WORDS)

A study of combined arm and leg exercise with application to nordic skiing.

A laboratory test was developed to study the metabolic and gas exchange effects of arm, leg and combined arm and leg work. The test incorporated movement patterns similar to those used in cross-country skiing. The work rate for the arm test at maximal effort was 33% (125 watts) and the leg test was 81% (302 watts) of that for the combined test (375 watts). The maximum oxygen uptake (VO2 max) was not significantly different when comparing the leg test to the combined test, but VO2 at submaximal work levels was significantly less during the combined test. The anaerobic threshold (AT) occurred at 68, 73 and 76% of VO2 max for the arm, leg, and combined test, respectively. Although there were no significant differences in VO2 and percent of VO2 max, at the AT between the leg test and the combined test, AT was significantly delayed with respect to time and work rate in the latter condition. Application of these results to cross-country skiing supports the proposal for greater upper body involvement in skiing.