After knee replacement surgery, what many people who love sport care about most is whether they can still run or play ball. This question has two quite different answers, depending on whether the sport is "low impact" or "high impact". If no distinction is made and everything is lumped together, it is easy to go to one of two extremes: either giving up exercise altogether out of too much worry, or going back to running and jumping regardless of the risk. Neither is ideal.
Put simply, most people can return to low-impact sports after knee replacement (such as swimming, cycling, walking and golf), generally from about 3 months after surgery, with the widest choice after 6 months. High-impact activities such as running, jumping and various ball sports raise the risk of wear of the artificial joint, so the medical consensus generally does not advise them, or considers that they should only be assessed case by case (Witjes 2016; Lester 2022). The sections below go through the trade-offs for each type of sport one by one, and explain the principle of wear.
Summary principle: low-impact sports can be done, and high-impact sports call for caution. Systematic reviews show that about seven to eight in ten patients return to physical activity after knee replacement, but over 90% of those activities are low impact, and the proportion who return to high-intensity sport is only about 35% (Witjes 2016; Hanreich 2020; Pasqualini 2023). Several expert consensus guidelines also agree in supporting low-impact sport and are reserved about high-impact sport (Lester 2022). The point is therefore not whether exercise is allowed, but how to choose a suitable type of exercise.
Classifying low-impact and high-impact sports
The first step to returning to sport safely is to be clear which impact level the target sport belongs to. An umbrella review that brought together several expert consensus guidelines divided sports broadly into three levels: low impact is widely supported, medium impact can be assessed individually, and high impact lacks enough supporting evidence (Lester 2022). The European knee expert consensus rates 47 common sports one by one and advises opening them up step by step with time after surgery (Thaler 2021). By degree of impact they are classified as follows:
- Swimming and aqua fitness
- Stationary cycling and cycling on the flat
- Walking on the flat, brisk walking and golf
- Doubles tennis and similar are medium impact and can be assessed individually
- Running and jogging
- Jumping and rope skipping
- Ball sports with sudden stops and turns, such as singles tennis and badminton
- Frequent downhill hiking and contact or collision sports
It is worth noting that even for the same sport, the degree of impact is affected by the venue and intensity. For example, riding a stationary bike indoors puts far less overload on the joint than cycling on a rough hill track, and doubles tennis is clearly gentler than singles. If there is still doubt about whether particular movements (such as kneeling to pick up a ball or squatting to tie a shoelace) are safe, this concerns the knee's ability to kneel and squat. See when you can kneel and squat after knee replacement.
How high-impact sport affects wear of the artificial joint
The medical community is reserved about high-impact sport, and this is not based on experience alone. There are clear biomechanical data behind it. The weight-bearing surface of an artificial knee is a polyethylene (plastic) insert, and when it takes repeated high peak loads for a long time, this plastic insert is overloaded and wears faster. The debris from wear may also cause bone resorption around the implant, and finally shorten the life of the artificial joint. A biomechanical study measured the overloaded area of the polyethylene insert caused by different sports, and the results showed very large differences between sports:
Low-overload activities (safe range)
- Cycling: overloaded area of the polyethylene insert of the artificial joint under 15 square millimetres
- Brisk walking: overloaded area under 50 square millimetres
- These activities are suited to keeping up in the long term after knee replacement (Kuster 2000)
High-overload activities (avoid as far as possible)
- Downhill hiking and jogging: overloaded area more than 140 square millimetres
- The peak load when the feet land reaches 8 to 9 times body weight, with the knee bent 40 to 50 degrees at the time
- The study advises avoiding jogging-type sport, and using hiking poles for support when going downhill (Kuster 2000)
In other words, the overload that jogging puts on the artificial joint insert is more than three times that of brisk walking, and nearly ten times that of cycling. This is the fundamental reason why running and frequent downhill walking are put on the list for caution. A person who likes hiking and wants to enjoy it again step by step after surgery is advised to choose flat or gently sloping routes, and to use hiking poles to share the impact on the operated knee at each landing, aiming to bring the joint load down from "high overload" to the safe range of "low overload".
Timetable for returning to sport: low impact cleared at about 3 months, widest choice at 6 months
When sport can resume after surgery depends on the patient's actual fitness and stage of recovery, and not on a fixed date alone. Putting together the results of several studies, the rough order for returning to sport is to start with low-impact sports and raise the difficulty step by step with each month after surgery:
What the medical community thinks of running after knee replacement
Among all sports, running is the one that knee replacement patients worry about most, and also the most controversial. The traditional orthopaedic position generally advises patients not to run again, because running carries both of the risks of "high impact" and "high overload". In recent years, however, the attitude of the medical community has changed somewhat, and the arguments on both sides deserve an objective look:
- The traditional reasons for advising against it—Jogging overloads the polyethylene insert over an area of more than 140 square millimetres, and the peak load at the moment of landing is as high as 8 to 9 times body weight (Kuster 2000). Because repeated impact speeds up wear of the insert and shortens the life of the artificial joint, it has long been listed as not advised.
- Recent observations that ease the position—A recent systematic review pointed out that the rate of complications caused by running after knee replacement is in fact low, and the attitude of the medical community to running is more open than before. The study also put forward a programme combined with structured rehabilitation training that lets patients take up running again step by step from about 6 to 8 months after surgery (Faldini 2025).
- But it still calls for careful individual assessment—However, the programme above is still at the trial stage and has no complete effectiveness data behind it. Also, the overall proportion who can return to high-intensity sport after knee replacement is only about 35% (Pasqualini 2023), and not every patient is in a position to do it. Whether running again suits the person must be discussed in detail with the orthopaedic doctor and the physiotherapist, and assessed carefully case by case.
Personal factors that affect whether sport can be resumed after surgery
Two people can have the same knee replacement operation, and one can go back to golf or even a jog on the flat after recovery while the other finds even walking on the flat hard. This difference depends to a large extent on the patient's own situation. Understanding the key factors below explains why the return to sport after surgery has to be assessed individually and cannot be generalised:
- Sports experience before surgery—The umbrella review pointed out that whether the patient took part in that sport before surgery is the strongest predictor. Put simply, a person who could already cycle or swim has a clearly higher chance of resuming similar sport after surgery (Lester 2022).
- Fitness and strength before surgery—Different studies show that the proportion who return to sport successfully after knee replacement ranges from 34% to 100%, a very wide gap. This reflects that the fitness base before surgery (especially quadriceps strength and balance) is a key factor. Training up fitness before surgery has a direct effect on how many kinds of activity can be resumed after it (Witjes 2016; Lester 2022).
- Type of replacement and kind of sport—Patients who have a unicompartmental knee replacement (that is, a half knee replacement) generally return to sport at a higher rate than those who have a total knee replacement. In addition, whether the target sport is low or high impact directly decides how hard it is and when it can be resumed (Witjes 2016).
How to return to exercise safely in Hong Kong
In Hong Kong, many older adults live after knee replacement in tenement buildings without a lift or in older buildings that need stairs, so going up and down stairs every day already puts a moderate load on the knee joint. Many patients also had a habit before surgery of morning hikes, tai chi in the park or an easy jog around the housing estate, and after surgery they are often impatient to get back to their usual way of life. When a physiotherapist visits for an assessment, they often meet patients keen to rejoin the morning run or the hiking group. In this situation the therapist does not ban all exercise across the board, but classifies the patient's existing exercise habits one by one according to the biomechanical risk of wear of the artificial joint. Swimming, cycling on the flat, easy walking and golf are cleared first. For downhill hiking, hiking poles or flat routes are advised. Anything involving jumping, ball sports and running needs a further individual assessment according to the stage of recovery after surgery and lower-limb strength.
For patients who want to increase their exercise gradually within 6 months of surgery, the physiotherapist relaxes the activity limits step by step according to the timetable after surgery. The first 6 weeks focus mainly on stationary cycling, exercise in water and walking on the flat, and the difficulty is raised step by step only after 3 months. The whole process rests on quadriceps strengthening and balance training, to make sure the patient has enough strength and joint range of movement before increasing the amount of exercise, and so lower the risk of falls and joint overload. On the public side, the orthopaedic departments of public hospitals have a "total joint replacement scheduled surgery" service (https://www.ha.org.hk/visitor/ha_visitor_index.asp?Content_ID=221223&Lang=CHIB5) that provides related information before surgery, and after surgery the patient can also be referred to the community for follow-up rehabilitation through the Hospital Authority allied health (physiotherapy) clinics (https://www.ha.org.hk/visitor/ha_isf_result.asp?lang=CHIB5&service_code_id=462&service_type=AH).
Returning to sport is only one part of the whole journey back to normal life after surgery. When driving, going back to work, climbing stairs and even kneeling and squatting can be resumed each have different assessment criteria, and readers can go back to the timetable for returning to daily life and sport after knee replacement for the full picture. If the operation was a hip replacement and not a knee replacement, the activity limits and positions to avoid after surgery are different. See differences by joint in returning to activity after hip replacement. For the question of "whether you can still run or play ball after knee replacement", the registered physiotherapists at Nova Health can, through home physiotherapyvisits, assess and grade each sport according to the patient's current strength, stage of recovery and target sport, and draw up a safe plan for returning to sport tailored to the person, so the patient does not go back onto the court unprepared.