Before we go into much more detail, its really important to understand what is required from each position;
Goalkeeper – Doesn’t cover much ground running, uses full body throughout the game, should have good agility, quick reflexes and mobile.
Defenders – Should be physically strong and good in the air, and other than full backs aren’t necessarily known for their speed.
Central midfielders – Dependant on formation, they must be robust and able to get forward and be able to track back so must have a good engine and physical strength
Wide midfielders – Must have good agility, fast, a good engine and mobile. Wingers will cover most ground in most games.
Strikers – Should be strong to hold the ball up for other attackers and have good aerial presence as these are the ones teams rely on for goals.
I could go on forever.
Each position must have good strength and power. When doing strength training, you are building muscle to protect the joints and also become more physically robust in the game.
Power – In reality, all positions need power training as this develops your jump height and also influences how far you can kick / throw a ball.
With goalkeepers, the prime areas that are used in a game are shoulder, elbow, wrist, hip, knee and ankle joints, where as primarily outfielders are impacted through the hip, knee and ankle joints.
So although there are elements that both goalkeepers and outfielders can train together, arguably, goalkeepers need a different type of programme.