5 reasons players get substituted in American football?

In association football, a substitute is a player who is brought on to the pitch during a match in exchange for an existing player. Substitutions are generally made to replace a player who has become tired or injured, or who is performing poorly, or for tactical reasons (such as bringing a striker on in place of a defender). Unlike some sports (such as American football, ice hockey or kabaddi), but like in baseball, a player who has been substituted during a match takes no further part in it.

Most competitions only allow each team to make a maximum of three substitutions during a game and a fourth substitute during extra time, although more substitutions are often permitted in non-competitive fixtures such as friendlies. A fourth substitution in extra time was first implemented in recent tournaments, including the 2016 Summer Olympics, the 2017 FIFA Confederations Cup and the 2017 CONCACAF Gold Cup final.[1][2][3][4] A fourth substitute in extra time has been approved for use in the elimination rounds at the 2018 FIFA World Cup, the UEFA Champions League, and the UEFA Europa League.[,5][6] Each team nominates a number of players (typically between five and seven, depending on the competition) who may be used as substitutes; these players typically sit in the technical area with the coaches, and are said to be "on the bench". When the substitute enters the field of play it is said they have come on or have been brought on, while the player they are substituting for is coming off, or being brought off or substituted.

A player who is noted for frequently making appearances, or scoring important goals, as a substitute is often informally known as a "super sub".

Explanation:

exercising at a moderate intensity, and slowly increasing the duration.