Relationship Between Oxygen Uptake During Maximal Acceptable Lifting And Ventilatory Threshold In Healthy And Lowback Pain Subjects

Introduction
The lactate/ventilatory threshold) (VT) is a submaximal test for aerobic fitness. The oxygen uptake (VO2) at the VT is
strongly correlated with endurance performance during distance running and is reportedly a better predictor of
performance than the VO2max.1 Lifting is an integral task in many occupations, and therefore, it is important that the
physiological factors that determine lifting endurance be evaluated in a variety of populations. The peak VO2 during
repetitive incremental lifting and lowering (RILL) has been documented in healthy men and women.2 However, there is
no information related to the VT during this exercise mode. Ergonomists have used the psychophysical technique to
determine the maximal acceptable lifting load (MAL) that an individual can sustain for an 8-hour work-day without
experiencing undue fatigue.3,4 Therefore, the purpose of this investigation was to examine the VO2 relationships
between the: (1) MAL and VT, and (2) MAL and peak VO2 during RILL in healthy (H) and non-specific low back pain
(LBP) subjects.

Methods
Written informed consent was obtained from 12 H (mean ± SD for age = 39.2 ± 6.7 yrs, peak VO2 = 29.6 ± 4.2
ml/kg/min), 17 LBP-active (LBPA; mean ± SD for age = 32.2 ± 5.7 yrs, peak VO2 = 29.8 ± 7.4 ml/kg/min)) and 11
LBP-sedentary (LBPS; mean ± SD for age = 34.6 ± 6.3 yrs, peak VO2 = 27.6 ± 3.0 ml/kg/min)) subjects. Each subject
completed the RILL test in the first session using 2.5 kg increments every minute until voluntary fatigue. In the next
session, the subjects were asked to select the MAL for an 8-hour working day as previously described.3
Cardiorespiratory responses were measured during both tests using a wireless metabolic measurements system (V-Max
ST, Sensormedics , CA). The VT was detected from the gas exchange measurements as the intensity at which there was
a systematic increase in the ventilatory equivalent for oxygen, without a concomitant increase in the ventilatory
equivalent for carbon dioxide using the metabolic software. The steady state VO2 during the MAL was averaged and
used for comparison. Analysis of variance was used to compare the mean values of the VO2 at the MAL, VT and peak
exercise among the three groups. Pearson correlations were used to examine the pertinent VO2 relationships in each
group.

Results
No significant differences were observed among the three groups for the VO2 values at the MAL, VT and peak exercise.
Significant correlations were observed between the VO2 at the MAL and VT in all groups, with the common
variance (R2) ranging from 50% in H to 71% in the LBPA group. Similarly, the R2 values for the relationship
between the MAL and peak VO2 ranged from 72% in the H group to 91% in the LBPS group.

Discussion / Conclusions
To the best of our knowledge this is the first study to document the VT in H and LBP subjects. The fact that there was
no significant difference between the groups for the VO2 at each of these exercise intensities was somewhat surprising
as it was hypothesized that the patients with LBP would have lower values due to deconditioning or as a result of
premature termination of the test due to low back pain. In each of the three groups, moderate to strong correlations were
observed between the MAL and VT, and the MAL and peak VO2. However, since the latter correlations were stronger
in all three group, the evidence suggest that the ability to perform lifting tasks for an 8-hour working day (ie. the MAL)
is more dependent upon the peak VO2 rather than the VT.

References
[1]. Farrell et al. (1979). J Appl Physiol, 11, 338-344.
[2]. Kell R & Bhambhani Y. (2003). Eur J Appl Physiol, 90,1-9.
[3]. Legg AJ. (1981). Ergonomics, 24, 907-916.
[4]. Davis KG et al. (2000). Ergonomics 43, 143-159.
Acknowledgements: Funding from the Alberta Workers’ Compensation Board

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