 This is in contrast to the traditional assumption that the free energy barrier between the folded and unfolded states are large.Because downhill folding is difficult to measure experimentally, molecular dynamics and Monte Carlo simulations have been performed on fast-folding proteins to explore their folding kinetics.Proteins whose folding rate is at or near the folding "speed limit", whose timescales make their folding more accessible to simulation methods, may more commonly fold downhill.