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. Author manuscript; available in PMC: 2017 Mar 30.
Published in final edited form as: Rheumatol Int. 2017 Feb 25;37(4):469–478. doi: 10.1007/s00296-017-3672-y

Table 1.

Decisions made within the expert consensus meeting

Objectives Consensus
1) Determine the suitability of using METs as a key method for harmonising variables between cohorts To define PA in OA related cohorts, data will be converted to MET-min/week using the duration, frequency and type of PA matched to the corresponding MET within the Compendium of Physical Activities (21). Where METs are already calculated based on Compendium versions prior to 2011, these will be converted to current 2011 Compendium of Physical Activity MET scores.
2) Determine methods for treating missing components of MET-min/week calculation Duration & frequency
A standard 30 minute assumption for missing duration data was felt to be rather arbitrary, particularly as there are specific activities where the time of the activity will not reflect this duration (e.g., football 90 minutes, golf 4 hours). If a parameter of PA such as duration or frequency is missing, values will be assigned using data derived from nationally representative cohorts. This study has provided average durations (Appendix 1) and frequencies (Appendix 2) representative of a wide range of activities from both US and UK cohorts to be used when such parameters are missing.
Intensity
Where the parameter of intensity is not measured “moderate” or “general” intensity shall be used for the given activity according to Compendium of Physical Activities. For example:

  • Where intensity of walking is not given, assume standard walking intensity of 3.5 METs

  • Where intensity of bicycling is not given, assume bicycling intensity of 7.5 METs

  • Where there is no differentiation between walking and cycling (how long you 'walk or cycle'), assume a MET value of 5.5


Type
Where a list of examples is given and one single type of activity cannot be chosen, assume MET based on the average of all of the examples, e.g., light sport (such as bowling, golf with a cart, shuffleboard, and fishing). Average of these type examples = 3.3 METs according to the Compendium of Physical Activities 2011 (21).
Time period
When a cohort questionnaire asked about ‘last week’, assume this is a typical week. When asked about months per year and times per month, calculate an average week over entire year. When asked about times per month, divide by four for times per week.
Walking and cycling
Where walking or cycling has a separate domain, disregard any walking or cycling equivalent variable that is also noted in sport and recreation domain.
3) Assess the domains of physical activity: how to treat missing domains Without these domains it was believed there may be an underestimation in PA within these cohorts. Available household data are good quality, therefore it was decided to impute missing data when statistically possible.
4) Assess the domains of physical activity: the use of occupation as a PA domain in studies with OA as an outcome It was agreed that occupation will not be included as a domain when calculating weekly METs. Instead results will be stratified by levels of occupational activity.
Findings from the consensus meeting revealed a similar international technical consensus meeting and PA initiative recently began refining working categories into the following levels: heavy manual, light manual, light, sedentary (Kelly P: Personal communication). Occupations and occupation related tasks, which are commonly used within population cohort studies, have been categorised into these four levels of occupation, according to the PASE questionnaire, which can be used to stratify results (Appendix 3).
5) Evaluate the use of an OA-specific PA measure taking weight-bearing vs. non weight-bearing activity into consideration Agreement was made that the degree of weight-bearing or joint loading should be considered on a scale. A decision was made within the expert meeting for the working group to further assess the use of a joint loading type questionnaires and use findings to inform further expert decision making within the subsequent Delphi exercise.
It was proposed to use the joint impact and torsional load categorization, developed by Buckwalter and Lane (35) as an example to classify activities into low, moderate or high level of impact/torsional load. This was chosen particularly for its relevance to OA, having been used by other researchers looking at the relationship between joint loading activity and OA.
Activities within the study cohorts were then categorised according to these classifications. Any activities that were not described by Buckwalter and Lane (35) were evaluated by the experts and placed in comparable categories. Agreement was reached within the Delphi exercise for the joint loading categories of low, moderate and high and the activities placed within each category (see appendix 4 for table provided to experts).
6) Establish if thresholds based on national PA guidelines should be used to investigate the association of PA with OA Agreement was made to evaluate the dose-response of METs against risk of OA to provide data driven thresholds to define ‘inactivity’ or ‘insufficient activity’, rather than use an arbitrary threshold. The primary analysis will exclude occupational METs and a secondary analysis will use overall METs from all domains if possible.
Agreement that a guideline based on the number of steps per day needed to reduce the risk of OA would be a valuable metric for some people to measure their PA levels, although this would require further assumptions to be made in the process of converting MET values to steps. An attempt will be made to complete the conversion based on results, providing there is an inflection point for the reduced risk of OA.