Modern Pentathlete and Olympic silver medallist from London 2012, Samantha Murray is next to take you through a workout. Strengthen your core with this 15 minute workout.br br Warm up before starting this exercise:br br Reverse lunge into high knee drive - 45 secondsbr Glute bridge - 45 secondsbr Core and glute twist - 45 secondsbr Crunch up, lower legs - 45 secondsbr br Take 15 seconds break between each exercise. Do three rounds in total.