It is often controlled by the experimenter. Examples include time, duration of exercise, dose of drug, body mass, etc. Mean heart rates of BSC students exercising on stationary bicycles for 60 minutes. Make the title as specific as possible, but it must also be concise. It is usually written as a sentence fragment with the first letter capitalized.
Some people like to use declarative statements in figure titles.
Small but Important Details Label your axes and always include units. Always include the sample size, either in the title or in a separate legend. Here are some other pages you might like to see. Experimental Design and Hypothesis Forming. Basic Statistics for Physiologists.