It's just that keeping your heart rate in the target range during regular aerobic exercise has been shown to be safe and effective for increasing your aerobic fitness. Exercising above this range can be very uncomfortable and may increase your risk of injury.
Typical daily weight gains for feedlot animals ranges between 0.5kg to 2.5kg per day, while grass fed animals are somewhat lower than this. The following data was collected from a small beef cattle company in Dallarnil in Queensland (approximately 300km north of Brisbane).
A commercial steer or bull calf is expected to put on about 32 to 36 kg (71 to 79 lb) per month. A nine-month-old steer or bull is therefore expected to weigh about 250 to 270 kg (550 to 600 lb). Heifers will weigh at least 200 kg (440 lb) at eight months of age. Calves are usually weaned at about eight to nine months of age, but depending on the season and condition of the dam, they might be weaned earlier.