Doubts over my Sprinting training structure

Hi so I am 49M and am training twice a week with a sprinting coach. His background is that he s from Kenya and does a lot of Sunni g coaching including sprinting. Typically our 60 minute session starts with 2 minute jog and then followed by a routine of mix of Askips , B skips, pogos etc for ( minutes or so. Then we do 3 sets x 3 reps of sprinting … might be 60m or 80m or leases volume for 100m …. Till here it’s all fine but in between sets he makes me to crunches and other an exercises that I dont see relevance and have flagged it to him. His response has been that it will help unlock my back muscles and also if I flat my tummy … it will add to sprinting power… is this correct … should let we be doing some stretching in these breaks between sets to improve my leg lift etc …. My body is quite stiff due to years of weight training and urban lifestyle … anyways … I need some inputs in what should be done in between these sets that helps improve my running form and that I can suggest to my coach with some conviction .