Abstract
BackgroundKnee pain is studied mostly in older age groups, although in young adults it may be an indicator of future impaired musculoskeletal health. Therefore, the aim of this study was to examine the longitudinal association between knee pain and thigh muscle strength in young adult women and to explore the associations between muscle strength, body composition, physical activity and knee pain. MethodsThe PEAK-25 cohort consists of women aged 25 at baseline (N=1064). At the 10-year follow-up n=728 attended for DXA-measured body composition and muscle strength assessment and n=797 answered the questionnaire on health and lifestyle. Independent samples t-test was used to compare women with and without knee pain, Spearman correlation was used to test the longitudinal association between strength and knee pain.ResultsKnee pain was reported by one third of the women at follow-up (n=260, 33%), although physical activity levels were similar in those with and without pain (high level 50 vs 45 % (p= 0.18). Body composition differed, however. Women with knee pain had higher BMI (25.6 vs 24.1), fat mass index (9.2 vs 8.2) and % total body fat mass (34.7 vs 33.2). Simultaneously, they had lower % lean mass (total body 61.5 vs 62.8; legs 20.6 vs 21.0) and lower thigh muscle strength (extensors 184.9 vs 196.8, flexors 96.6 vs 100.9, p<0.05), but slightly higher hamstrings-to -quadriceps ratio (0.53 vs 0.51, p=0.04). Muscle strength at baseline weakly correlated with knee pain at follow-up (extensor rs= -0.04; flexor -0.02, p>0.2). Overweight women had higher absolute thigh muscle strength, but lower weight-adjusted strength than normal weight women (p<0.001). Leg lean mass explained 26-34% of the variation in muscle strength and adjustment for physical activity level had little effect.ConclusionKnee pain is already common among women in their mid-thirties. Lower thigh muscle strength in the mid-twenties was not associated with future knee pain, however women with knee pain tended to have lower thigh muscle strength and a body composition of higher body fat combined with lower lean mass. Maintaining a healthy body composition and adequate thigh muscle strength may be beneficial for knee joint health.
Highlights
Knee pain is studied mostly in older age groups, in young adults it may be an indicator of future impaired musculoskeletal health
With the hypothesis that strong thigh muscles may protect against knee pain we examined the longitudinal association between thigh muscle strength and knee pain in a population-based cohort of young adult women, assessed at age 25 and again 10 years later
Association between muscle strength and body composition To further understand the association between muscle strength and the body composition components, we firstly examined the relationship between thigh muscle strength and body fat mass, using the fat mass index (FMI) classifications normal weight, overweight and obese
Summary
Knee pain is studied mostly in older age groups, in young adults it may be an indicator of future impaired musculoskeletal health. Knee pain is common at all ages, but prevalence increases with age [1]. Women aged 50 years or older have a higher prevalence of knee pain than men, but in younger age groups both men and women have similar frequency of knee complaints [1]. In young women patellofemoral pain is common [4] and may increase the risk of femuropatellar osteoarthritis [5]. Known risk factors for knee pain are the same as for knee OA; heredity, female gender, higher age and knee injury, overweight and occupational high joint loading [6,7,8,9], this includes muscle weakness [10, 11]
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