1. How to read a code like T54 or F46, letter first and number second
The letter comes first. T stands for track and covers running, wheelchair racing on the track and road, and all the jumping events. F stands for field and covers the throwing events [1] [4]. The two digits then tell you two things. The tens digit points to a group of impairments: for example, visual impairments are in the tens (T11, T12, T13), and coordination impairments are in the thirties [1]. The last digit shows how significant the impairment is. The International Paralympic Committee (IPC) says that the lower the number within each impairment type, the more significant the impairment [1].
So the number is not a speed score. T54 is not "slower" or "faster" than T47; the two classes are simply about different bodies. Athletics Australia describes T54 as athletes with strong arm and torso movement who have an impairment in their legs, and they race in wheelchairs. F46 covers athletes with moderate limb loss, muscle weakness or restrictions that affect one arm. T64 is for athletes who have lost one leg below the knee and run with a prosthetic running leg [4]. Reading a code gives you a first picture of the athlete's body and equipment, before the race even starts.
2. Why are Para athletes split into classes when they run the same race?
Imagine a wheelchair racer, a runner with a prosthetic leg, and a runner with a guide all starting the same race on the same signal. They use different equipment and move different parts of their bodies, so it would be hard to tell how much each athlete's training, tactics and effort contributed to the result. The IPC explains that the system tries to put athletes with approximately the same amount of activity limitation in the same class, in the key activities of running, wheelchair racing, jumps and throws [1]. In its own words, classification aims to make sure the outcome of a competition is decided by factors other than impairment [3].
Sport does this in other places, too. In judo, athletes are put into weight classes. In some sports, such as football, men and women compete separately. In marathons, there are age categories [3]. Para athletics groups athletes by the effect of their impairment on the sport, and the World Para Athletics page says this is, to a certain extent, similar to grouping athletes by age, gender or weight [2].
There is a second job as well: deciding who may compete at all. Having an impairment is not enough. In Para athletics, a person needs one of 10 eligible impairment types and must also meet the minimum impairment criteria in the sport's rules [2]. The ten are: impaired muscle power, impaired passive range of movement, limb deficiency, leg length difference, short stature, hypertonia, ataxia, athetosis, vision impairment and intellectual impairment [2]. The page also stresses that classification is specific to each sport, because an impairment affects performance differently in different sports. An athlete might qualify in one sport and not in another [2].
3. What do the classes look like, and how does the class change the way an athlete competes?
The classes are grouped by the athlete's impairment and by how they compete. For running and jumping, World Para Athletics lists, among others: T11 to T13 for vision impairment, T20 for intellectual impairment, T40 and T41 for short stature, T42 to T44 for a leg affected while competing without a prosthesis, T45 to T47 for one or both arms affected, and T61 to T64 for athletes who compete with a prosthesis on one or both legs. Wheelchair racing has its own classes, T32 to T34 and T51 to T54. Throws follow the same pattern with the letter F, and seated throwing classes include F31 to F34 and F51 to F57 [2].
The vision classes show clearly how a one-digit difference changes the race. Athletics Australia explains that a T12 athlete has very low vision and has the option to use a guide, while a T13 athlete has low vision, with more vision than T12, and is not able to use a guide [4]. Below them is T11, the class with the most significant vision impairment, whose athletes run with a guide, according to an IPC feature [5]. A smaller number really does match a more significant impairment.
These lists change over time, so any class table is a snapshot. The Athletics Australia article notes that the 60s classes for prosthetic users were new for Tokyo 2020 [4]. For the current list, check the World Para Athletics page, which also reminds readers that its summary is not legally binding and that the full rules take precedence [2].
4. Who decides an athlete's class, and can it change?
Athletes are evaluated by classifiers, who work together in a group called a classification panel. Classifiers must be qualified and certified by the sport's international federation, and each one is trained for one impairment group: physical, vision or intellectual [3]. An evaluation session usually takes place in the days before an international competition. Beforehand, medical information is submitted so the federation can check that the athlete has an underlying health condition and an eligible impairment [3]. The panel's decisions are meant to be objective and based on the sport's classification rules [3].
A class is not always for life. The IPC explainer points out that athletes may not stay in the same class for their whole career, because some impairments are progressive and affect activities differently over time, so athletes are sometimes classified a number of times [1]. The IPC also records a "sport class status" for each athlete, which indicates whether and when the athlete may have to be classified again, for example when a condition changes or a sport's rules change [3]. Athletes cannot lodge a protest about a class themselves: the IPC says only a national federation or national Paralympic committee can do that [3].
One limit of what I could check: the sources I read describe who decides and when, but not the detailed tests a panel uses for each class. Those are in the sport's full classification rules, which are linked from the World Para Athletics page [2].
5. Try reading the codes yourself next time you watch
When a code appears on screen, ask three questions in order. Is it T or F? What group does the tens digit point to? And within that group, is the last digit low (more significant impairment) or high? Try these three: T11 is a vision class, and one IPC summary says its athletes run with a guide (check the current rules to confirm) [5]; F46 is a standing throwing class for athletes whose impairment affects one arm [4]; T64 is a running class for athletes who use a prosthetic running leg [4]. Then look for the athlete's class table on the World Para Athletics page and see whether your guess matches.
It is also worth asking whether you think grouping by impairment is the fairest idea, and how else it could be done. That is exactly the question the classification experts keep working on, and the IPC has a research page on it [3].