Athletes are often confused about Split Interval work outs in the pool. Unlike rest interval workouts, you do not have a prescribed rest at the end of the work interval. Instead, the approach is to give you a defined time box to complete each work interval & the time box includes any rest you are allowed.
E.g. Swim 400 @T-pace+10 SI.
Let’s assume your T-pace is 2:00/100 yards. This would mean you have 2:10 * 4 = 8:40 to complete the 400 including your rest. Your goal is to beat the clock to get that rest. Typically SI workouts allow you adequate time to complete the work and get a very short rest. Note: Very short.
Don’t race for your rest, pace for your rest. SI workouts tend to be quite long. The trick is to swim it slower than you can and still get a little rest. As you get better, you will end up swimming faster & getting more rest. This indicates mastery and you are probably ready for a new T-Pace test to reset your T-Pace or alternatively complete more yards.
I often find athletes sneaking in supplemental rests. This is naughty. These workouts are stamina builders. If you managing the workout continue as prescribed. If you find your self falling behind the clock, it simply means you have fatigued out. Take a 30 second rest immediately, regroup, and then pursue the clock as before.
Remember, no rest for you.