My ex was a solid cyclist. Speeds that were just effortless to him were gasping-for-breath-blowing-snot strenuous to me. While I've sped up a little, recently, at that point it always felt like I was holding him back. =P Then again, when he got car-biffed it was a good thing I wasn't right behind him. I can only smile about it now because he was okay... at the time it was terrifying.