Table 1.

Characteristics of those with no history of swimming, any history of swimming, all participants, and those excluded from these analyses.

Participant Characteristics	Non-Swimmers (n = 1575)	Swimmers (n =1062)	All Participants (n = 2637)	OAI Participants seen at 96-month visit before 9/12/12 who did not complete the historic physical activity survey (n = 699)	OAI Participants eligible for historic physical activity survey, but did not complete questionnaire (n = 618)
Age (years) (at the OAI 48 month visit)	64.1 (9.0)	64.7 (8.9)	64.3 (8.9)	65.4 (8.5)	67.0 (9.4)
Sex (% Male)	48.5%	37.9%	44.2%	32.5%	38.8%
Body Mass Index (kg/m2) (at the OAI 36 month visit)	28.7 (4.8)	28.1 (4.9)	28.4 (4.9)	28.7 (5.1)	29.1 (5.2)
Body Mass Index at age 25 (kg/m2)	23.2 (3.2)	22.8 (3.3)	23.0 (3.2)	22.7 (3.5)	23.1 (3.4)
Frequent knee symptoms (at the OAI 48 month visit) (%)*	40.1%	36.9%	39.3%	50.4%	48.5%
Radiographic Knee Osteoarthritis (at the OAI 48 month visit) (%)*	59.5%	53.9%	57.3%	65.7%	62.9%
Symptomatic Knee Osteoarthritis (at the OAI 48 month visit) (%)*	29.4%	24.4%	27.4%	37.0%	38.7%
History of Total Knee Arthroplasty (by the OAI 48 month visit) (%)*	4.6%	3.2%	4.0%	7.0%	6.2%
History of Knee Injury (%)*	48.0%	47.0%	47.6%	55.5%	47.6%

^*Knee-based characteristic (within person measure)