It’s not easy going about daily life and self-care if your knees are always sore or stiff. But that’s the harsh reality facing a rising number of older people in Hong Kong with osteoarthritis of the knee, or knee OA. Besides treatment and physiotherapy, doing tai chi or other land-based exercise can benefit many knee OA patients. However, some are unable to bear a large amount of their body weight on their arthritic knee because of the pain. Special, physiotherapist-led aquatic exercise programmes conducted in a warm pool could help them, but their long-term cost may be prohibitive. Could Ai Chi, an aquatic exercise incorporating tai chi concepts, be a sustainable alternative?

Knee OA occurs when the protective cartilage inside the knee joint thins, which eventually causes the bones in the knee joint to rub against each other. Previous studies of the special aquatic exercise programmes showed they could help improve knee OA patients’ pain, stiffness, balance, physical functioning, and quality of life, with the water’s warmth, supportive buoyancy and slightly compressive pressure aiding in the easing of pain and the relaxation of muscles. However, their dependence on the presence of a physiotherapist to provide instruction could make them unsustainable in terms of manpower availability and cost because of Hong Kong’s ageing population, with a third of people aged 65 years or older in 2050 in the city forecasted to have knee OA.

In the first study of its kind, a research team from PolyU’s Department of Rehabilitation Sciences led by Clinical Associate Dr Billy So and Associate Professor Dr William Tsang decided to investigate whether Ai Chi aquatic exercise could improve knee OA patients’ pain, stiffness, proprioception (or sensing the position and movement of the knee without visual and auditory clues), and physical function and quality of life. Similarly with tai chi, Ai Chi involves the slow execution of standard movements to controlled breathing and uses no accessories, with trained individuals free to practise on their own afterwards.

With the help of the Chinese YMCA and private clinics in Hong Kong, 27 consenting knee OA patients between 50 and 65 years old who also satisfied the pilot study’s medical criteria (to ensure their suitability as well as safety) were recruited as subjects. They underwent a 10-session Ai Chi training programme over a 5-week period to learn the first 16 of the 19 standard Ai Chi movements under the supervision of a physiotherapist. Each of the 2 sessions per week lasted an hour and was conducted in a warm pool (at 31˚C) that was 1.2 m deep. The subjects were asked to half-squat so that the water would come up to shoulder height, resulting in their arm, torso and leg movements being under water. The subjects were assessed for knee pain, stiffness, proprioception, and physical function and quality of life just before the start and just after the end of the programme, as well as for any worsening of pain just before the start, after the ‘midway’ 5th session, and just after the end of the programme. They were also asked to self-rate their physical health and mental health using a questionnaire just before the start and just after the end of the programme.

Each of the movements was introduced incrementally according to a pre-determined schedule, with subjects asked to repeat each new movement 3 times on both their left and right sides. Subjects who had been taught all 16 movements were deemed to have completed the programme, regardless of how accurately they could perform the movements.

Research data of 2 subjects were excluded from the analysis and results because they both failed a couple of medical criteria during the study. Of the remaining 25 subjects, 23 had attended at least 8 of the 10 Ai Chi sessions.

Dr So, Dr Tsang and their colleagues found the 25 subjects’ self-ratings of pain, stiffness, and physical function (as measured by the Western Ontario and McMaster Universities Osteoarthritis Index) had improved significantly. However, few statistically significant changes were found in stiffness and physical function from objective assessments (using other instruments on other physical capabilities), possibly owing to the small sample size.

In addition, without control subjects, it was difficult to separate how much of the self-rated improvement in pain was the result of exercising in a warm pool as opposed to from performing Ai Chi per se. Notably, there was no significant improvement in the self-rated aggravating pain score between the assessment after the 5th session and the assessment after the 10th session, possibly because of the latter sessions’ more challenging movements and a slowdown in pain reduction rate after the novice subjects had underwent the first few sessions.

Objective measurements of stiffness showed no significant improvements except for a significant increase in the range of passive extension (or ‘straightening’) of the more arthritic knee. The research team noted that most of the subjects had a nearly normal range of motion just before the programme started and they half-squatted during the sessions, so it was not unexpected there were no significant changes in range of motion.

There was no significant change in the subjects’ physical function as measured by a standard 6-min walking test along a suitable indoor corridor. This could be because Ai Chi, being water-based, required relatively low exertion by the subjects, perhaps insufficient to improve their muscle endurance and cardiovascular fitness to the extent that it would manifest as a significant improvement in distance walked.

Similarly, the buoyancy of water could have contributed to the lack of significant improvement in knee proprioception. A previous study found tai chi could improve knee proprioception in experienced elderly tai chi practitioners. But the reduced loading on the legs of the current study’s subjects could have lowered their legs’ muscle activity and hence stimulation of their legs’ internal sensory receptors that are involved in generating proprioceptive information. The research team also pointed out that the 5-week period of Ai Chi training might have been too short to have resulted in sufficient neural adaptations in the novice subjects’ brains in response to the new movements for knee proprioception to have improved, compared with the several years of tai chi practice by the previous study’s subjects.

There was no significant change in the self-ratings of physical health, which the research team observed was inconsistent with the findings of a previous study of aquatic therapy on knee OA patients. However, there was no significant change in the self-ratings of mental health, which was consistent with previous studies of aquatic therapy and not unexpected since the current study’s subjects had a similar average baseline mental health score to that of healthy people of the same age.

Despite the pilot study’s lack of significant ‘objective’ results, the significant improvements in the self-ratings of pain, stiffness, and physical function suggest that Ai Chi is worth exploring further as a possible sustainable option to physio-led aquatic exercise.