Physiological Comparisons of Elite Male Visma Ski Classics and National Level Cross-Country Skiers During Uphill Treadmill Roller Skiing. - Sagelv EH; Engseth TP; Pedersen S; Pettersen SA; Mathisen G; Heitmann KA; Welde B; Thomassen TO; Stöggl TL (Frontiers in physiology, 2018)