Falls in daily life are a serious risk for people with stroke. A new type of balance training, called reactive balance training (RBT). may help to reduce this risk of falling. In some previous studies participants improved their balance reactions a lot after RBT, whereas others did not improve at all. These studies used different types and amounts of training. Differences in training program features might explain differences in the study results. Training intensity is the difficulty or challenge of the training program. For other types of exercise (like 'cardio' or strength training) if the intensity of exercise is increased, someone can get the same benefits in less time than with lower intensity exercise. Physiotherapists report that they have limited time in rehabilitation to do everything they need to do with their stroke patients, so it would be valuable to know if high-intensity RBT improves balance reactions quickly. The goal of this study is to see if more intense RBT improves balance reactions faster than less intense RBT. People with chronic stroke will be randomly placed in one of three groups: high-intensity RBT, moderate-intensity RBT, or a walking control group. The investigators will find the fastest moving platform speed that participants can respond to with single step (multi-step threshold). There will then be 4 1-hour long training sessions in one week. Participants in the high-intensity group will experience platform movements that are 50% faster than the multi-step threshold. Participants in the moderate-intensity group will experience platform movements at the multi-step threshold. Participants in both RBT groups will experience 36 multi-directional platform movements in each training session, causing them to start to fall forwards, to the left, or to the right. Participants in the walking group will walk on the platform 36 times without any platform movements. The investigators will measure how quickly people improve their balance reactions over the training program.