Sunday a day of rest? Pah! Get yourself to the cable machine, connect the ankle/foot strap to the lowest point on the bar and set the weight at around 3kg to start with.

Cable Kickbacks

Angle forward with a long, straight back and hold on to the bar for stability then simple start doing donkey kicks - nothing severe. Two counts in, two counts back with control! After 12, your glutes and hamstrings should be exhausted. Swap sides. Repeat 3 times.
Outfit: myescape
Shoes: The North Face