The purpose of this randomized, controlled trial is to determine whether a vibration platform exercise program will be more effective than a standard platform exercise program in improving quadriceps strength in women age 45-60 who have risk factors for knee osteoarthritis. Each platform exercise program will be conducted 2 times a week for 12 weeks. The sessions will consist of a series of exercises on a Wave Pro-elite vibration platform (with 1-3 minute rests between sets) and stretches with the platform vibration either turned on (intervention group) or off (control group.) Quadriceps strength (primary outcome), leg press power, and vibration sense will be assessed at baseline and 12 weeks, and changed scores will be compared between groups.

Osteoarthritis (OA) is the most common disabling disease in older adults,(1) affecting over 25 million Americans, resulting in significantly impaired function and mobility(2) and a societal economic burden.(3) The knee is the weight-bearing joint most commonly affected,(10) and the prevalence of symptomatic knee OA is between 9% and 21% among those 65 years and older.(2, 11, 21) Loss of knee range of motion can lead to significant difficulty in bathing, lower body dressing, stair mobility, and walking.

Impaired mobility due to knee OA will have an increasingly significant societal impact, with 67 million adults projected to have arthritis by 2030, and 25 million with arthritis-attributable activity limitations.(22) Women are at greater risk for knee OA compared with men. Knee OA leads to chronic disability,(23-25) functional limitations,(26) and dependence.(27) Patients with knee OA frequently are limited in their activities by joint stiffness or buckling, decreased range of motion, muscle weakness, poor balance, impaired proprioception, reduced vibration sense, and/or pain. Currently, there are limited options available for patients for improving the outcome of knee OA once they have it. At this time, patients may use analgesics for pain with total knee replacement as the last option. However, we recently found that greater quadriceps strength protected against the development of incident symptomatic knee OA and progression of knee OA in women.(19-20) Thus, strengthening the quadriceps muscle may prevent worsening of the knee joint. Though before studying whether strengthening is effective in reducing risk for knee OA, it is necessary to first determine an effective and tolerated means of exercise.

Vibration platform exercise may provide the benefits of strength training without adding potentially harmful loads to the knee joint. In one study of nursing home residents with limited functional capacity, balance and mobility improved over a 6-week whole body vibration exercise program. (12) In another study that compared whole body vibration (WBV) to resistance training in older women, greater improvement in knee extensor strength and speed of movement was found with WBV exercise.(13) Additionally, after a 2-month exercise program with older adults between the ages of 59 to 86, walking speed, step length, and the maximum standing time on one leg significantly improved with WBV exercise.(14) WBV exercise was safe and well tolerated in the elderly.(14, 15, 16) There have also been indications that WBV may improve flexibility. While a study testing range of motion (ROM) found that both the WBV and the control groups had significant increases in hamstring flexibility, only the WBV group showed a significantly larger increase (30%) in ROM than did the control group (14%).(17) There have also been indications WBV may improve proprioception (joint position sense) in women with knee osteoarthritis. One study which compared control versus exercise on a vibration platform and a balance board vibration platform found improvements in muscle strength and proprioception, respectively.(18) Thus, these studies suggest a beneficial effect of WBV exercise in addition to muscle strengthening, balance, and walking exercises in improving the walking ability in the elderly.

Exercises conducted on a vibrating platform will induce a muscle reflex, increasing muscle fiber activation at a higher level compared to performing the exercises on a non-vibrating platform. We have selected the frequency and duration of this program based on 1) frequency used in previous studies and recommended by the manufacturer and 2) duration of 12 weeks based on previous data which found the most gain in knee extensor strength and speed of the movement occurred at week 12 of a 24-week program. (13)

Vibration exercise may be a better option than strength training alone, if the exercises can be completed in less time and with similar strength gains as resistance training, but without the additional loads contributing to the stress on patients' joints.

Inclusion Criteria:

• age 45-60
• female
• history of knee injury or surgery (except replacement surgery) or body mass index (BMI) greater than or equal to 25.

Exclusion Criteria:

• diagnosis of knee osteoarthritis
• inflammatory arthritis such as rheumatoid or psoriatic arthritis
• knee replacement
• metallic implant or stent placement surgery or any implanted devices
• surgery or lower limb injury in the last 6 months that affects walking ability
• lower limb amputation (other than single ray)
• unable to walk without an assistive device
• wounds that contraindicate weight-bearing exercise
• acute infection or inflammation that contraindicates exercise
• acute disk related problems (new lower back pain in the last 3 months or severe enough to affect walking)
• osteonecrosis
• currently pregnant or planning to become pregnant
• kidney, bladder or gallstones that have not been passed
• retinal detachment
• ever experienced deep vein thrombosis
• type 1 diabetes mellitus (insulin dependent)
• history of myocardial infarction or stroke in the last year
• medical conditions that affect walking ability or ability to take part in the study or exercise such as; Alzheimer's disease, multiple sclerosis, Parkinson's disease, severe cardiovascular disease, congestive heart failure, severe emphysema, severe asthma, severe dysrhythmias or pacemaker
• Any type of implanted pump (e.g. Morphine, baclofen) or catheter (e.g. In kidney, brain or spine)
• neuropathy (by Semmes-Weinstein Monofilament)
• uncontrolled epilepsy
• active cancer (< 5 years since remission) or other illness expected to be terminal within 1 year
• concurrent participation in another research study
• Inability to follow protocol (e.g. lack of ability to attend visits or understand instructions)
• frequent knee pain on most of the last 30 days