What does Jaunty strains mean

A noun with an adjective

Explanation:

Strains is the noun, plural, and the singular form means:

A force tending to pull or stretch something to an extreme or damaging degree.

Jaunty is the adjective which means:

Full of confidence and energy.

So, when put together we are talking а bout:

Forces pulling or stretching something noun part

in a confident and energetic way adjective part

I could think of a physical exercise that can produce Jaunty strains