nervous

"Muscle consists largely of actin and myosin filaments."

"The weightlifter's sinews tightened as he lifted the heavy barbell. "

"tensing a verb"

"I went to the park because the weather was nice. "

"The nerves can be seen through the skin."

"The athlete stretched her tendons carefully before practicing her jumps. "

"The drivers were racing around the track."

"He is a student of life."

"The school's dance troupe has a talented dancer who practices every day after school. "

"My grandmother used a soft felt hat for her winter walks. "

"Before dinner, I finished my homework. "

"the performance of an undertaking or a duty"