Foam rolling can be a useful part of managing a build up in tightness and trigger points created by those hard running, bike or pool miles. It is a form of self massage or self myo-fascial and whilst it doesn't replace the need for regular stretching and sports massage can provide effective routine 'maintenance'. It's not the whole answer though and the peer reviewed science is still limited but there certainly are studies to back up it's use to complement the thousands of anecdotal examples you'll find form athletes online - https://www.ncbi.nlm.nih.gov/pubmed/26618062
Foam rollers are cheap and readily available these days. Most are simple rolls of dense foam. The density determines how intense your 'self massage' will be, blue and white colours often represent a slightly less dense, softer roller, back a high density, hard massage. You can even find rollers (such as the one in our pictures) which have nodules on to assist in breaking down those trigger points and knots.
Once you have the correct roller for you start by gently rolling up and down the massage muscles form the images below at about 1-2 inches per second. As you do this you will likely find specific points of more intense discomfort, or areas of the muscle that feel 'lumpy'. On these areas stay in place for 10-20 seconds on the point of discomfort and gently move your body fractionally from side to side. During the course of the 10-20 seconds you should find the pain gradually dissipate, then continue 'rolling' moving onto the next trigger point.
Avoid foam rolling directly over a joint, injured tendon, muscle or bone or on your lower back. You can vary the intensity by changing the surface underneath the foam roller or by applying additional bodyweight onto the muscle being treated (see the calf image below). Traditionally foam rolling is completed after training or on easy or rest days before stretching. Increasingly, however, physiotherapists and strength and conditioning coaches are recommending a short, low intensity period of foam rolling pre-training. Foam rolling stimulates the golgi-tendon organ proprioceptor, which senses muscle tension. Stretching affects the other proprioceptor within your muscles - the muscle spindle. We need to work both to both, therefore have a play around with short 3-5 minute period of foam rolling before some of your easy runs to feel if it helps you. If you are under the instruction of a physiotherapist or have any potential contraindications to using a foam roller check it out with your physio first.