Every run interval training starts with a warm up. The run sessions are so intense that they are known to get you injured quickly if you do not warm up properly. This counts for beginners and pro athletes. I recommend to start every session with a 1.500 meter warm up jog and a intensive stretch session. After the interval training is done you cool down with a final 1.500 meter jog and a stretch session.
Try to mix up these interval training sessions with hill sprints.
Again make sure you are warmed up once you start with bike interval training. Start all sessions with a 20 minute warm up ride and finish them with a 15 minutes cool down session. The total interval bike sessions last no longer than 1 hour.
Yes you need to warm up and cool down with swimming as well. Start with a 400 meters warm up swim where you focus on your technique, make sure you float well and stretch out with those arms. Cool down with another 400 meters and these can be mixed up with breast strokes too.
Let me guarantee you that with these training sessions you will improve your overall strength and develop more race speed.