“fartlek” • Ability • Ancient • Athletes • Based • Breathing • Bursts • Cardiovascular • Different • Done • During • Efficiency • Exclusively • Fast • Faster • Flexible • Follow • From • Gösta • Hills • Incorporating • Individual • Intensity • Interval • Intervals • Japanese • Long • Maintain • Number • Overall • Periods • Play.” • Requires • Roads • Runner • Same • Short • Should • Slow • Specific • Speed • Term • Tracks • Treadmill • Twitch • Unstructured • Was • Weightlifting • Which • Word