Identify the exercise routine that most effectively demonstrates an improvement in cardiorespiratory fitness.

Walking briskly for 30 minutes, three times per week, without increasing intensity over time

Performing 4 × 4-minute high-intensity intervals, three times per week, with short recovery periods

Cycling for 45 minutes at moderate intensity, five times per week, gradually increasing duration or intensity

Lifting weights for 45 minutes, three times per week, with a brief 10-minute low-intensity warm-up