Shelby performed an investigation in which she monitored her heart rate while she ran on a treadmill. She used a heart rate monitor before she started running and determined that her resting heart rate was 62 beats per minute. After 10 minutes of running, the heart rate monitor showed that Shelby's heart rate was 141 beats per minute. What was Shelby's blood delivering to her cells at an increased rate as her heart rate increased? ATP carbon dioxide oxygen lactic acid