As a multidimensional sport that places a variety of physical demands on the athletes, rugby training must be comprehensive in its scope. Every player on the field must possess a basic level of ability in the five major physical components of the of rugby: running, tackling, ball carrying, passing, and kicking. The various rugby-specific techniques needed to advance the abilities of the player cannot exist without these fundamentals.
Each of these fundamental skills must be developed in relation to the position played by the athlete. Rugby has 15 players per team (often referred to as a side), of whom eight are "forwards," who play in the more physical "pack" that scrums the ball. The forwards are primarily responsible for creating a territorial advantage for the team on the field. The remaining seven players are the "backs," who are aligned behind the forwards, starting with the scrum half who handles the ball most frequently, fanning out to the wing.
As a general rule, the forwards are the largest and strongest rugby players, and the backs are the most adept in ball handling, kicking, and running. While no successful rugby player can be a one-dimensional player, responsible for a limited series of physical tasks, the strength training and exercises devised for rugby athletes must balance the overall skills required by all players with those that are position-specific.
The strength training applicable to all rugby players will require overall muscular explosiveness, both in delivering a tackle, as well as in developing the acceleration necessary to sprint effectively. Players also need muscular endurance both to compete throughout an 80-minute game and to effectively recover from that exertion. Besides coordination and agility, musculoskeletal flexibility is important for the players. The better the range of motion the athletes can develop in the joints, the more responsive and the less likely they are to sustain a serious joint injury. For flexibility, conventional free weight training and dedicated stretching and flexibility exercises are most useful. Another critical component for players is muscular balance, particularly between the quadriceps and the hamstrings, which are subjected to both the stresses of running as well as the forces of tackling. A balance of the respective strengths of the quadriceps to the hamstrings in the approximate ratio of 3:2 is the goal.
The specific training needs of the forwards begin with their considerable size. At an international level, a forward may run over 3,000 yd (2,700 m) in the course of a contest. It is not uncommon for an elite forward to weight over 240 lb (109 kg); the larger the athlete, the more difficult the player will be to either tackle or to push in the opposing scrum. Comprehensive rugby forward training is an application of the principles of developing an ideal strength-to-weight ratio. Endurance training that is less stressful on the athlete's legs and joints is cycling or swimming. For the large player interval running achieves the dual effect of both running training and building the speed and explosiveness necessary on the field.
The forwards must possess overall muscular strength; much of the physical efforts they expend during a game are in the scrum, where significant energy is delivered through the drive of the athletes' legs to move the scrum forward. Leg training, such as squats, is provided by a scrum machine—a device constructed on a weighted sled—and replicates the forces experienced in the scrum. The scrum machine employs the same training principles as the American football blocking sled; it is a useful strength trainer because the athlete may derive the benefits of resistance and the opportunity to practice particular physical techniques used in scrum play.
The success of a rugby back will blend focused strength training, particularly in developing both speed and running power, with the muscular strength to combat tackles delivered by fast-moving or much larger players. Running training must emphasize the explosive nature of rugby, with both straight ahead and lateral movement. Plyometrics training and interval running assist in this development. Agility training may be incorporated into basic running movements through zig zag drills, where the athlete follows a predetermined pattern on a field or playing surface. Intervals that require the player to move backward, to simulate the fielding of a rugby kick (retro running), also build strength, reaction, and leg muscle balance.
The backs must also possess an appropriate strength to weight ratio, for reasons counter to those of the forwards. A rugby back may run upward of 5,000 yards (4,500 m) in a game, much of the distance covered at a significant speed. The back must be light enough to move quickly, yet strong enough to sustain the multitude of blows encountered during an 80-minute game.