It's well known that physical exercise is beneficial not just to physical health but also to mental health. Yet whereas most countries have ___26___, evidence-backed guidelines on the type and intensity of exercise ___27___ for various physical health benefits, such guidelines do not yet exist for exercise and mood. This is ___28___ due to a lack of necessary evidence. However, a new systematic review brings us usefully up-to-date on the current findings in this area.

Before ___29___ into some of the key take-aways, an important ___30___ made in the review is between aerobic exercise and anaerobic. The former ___31___ such things as walking, jogging and cycling and means exercising in such a way that your body is able to use oxygen to burn fat for energy. In contrast, anaerobic exercise-such as lifting heavy weights-is of such ___32___ intensity that your body does not have time to use oxygen to create energy and so instead it breaks down glucose (葡萄糖) in your blood or muscles.

Beginning first with the influence of exercise intensity on the mood benefits of aerobic exercise, the researchers, led by John Chan at Shenzhen University, found ___33___ results from 19 relevant studies. Some favoured higher intensity, others low, while seven studies found that intensity made no ___34___ to mood benefits.

In relation to the intensity of anaerobic exercise, however, the results were far clearer—the optimum (最佳选择) for improving mood is ___35___ intensity, perhaps because low intensity is too dull while high intensity is too unpleasant.