Sue would like to improve the flexibility of her calf muscles. Which of the following static training thresholds would you recommend?
A) hold stretch for 6 seconds, perform a single repetition, 7 days per week
B) hold stretch 10 seconds, perform 4 repetitions, once per week
C) hold stretch 15 seconds, perform a single repetition, once per week
D) hold stretch 15 seconds, perform 4 repetitions, 3 days per week