Strength training in football

Strength is thought to plays a role in injury prevention (6, 21, 23, 29, 44, 54, 61, 73) as well as in football performance (17, 48, 52, 63, 65, 70, 78, 79, 83, 92) in adults (5, 12, 17, 52, 54, 56, 65, 67, 78, 79, 83, 92) and female (61) and male youth players (15).

Leg strength, measured with a squat (4) or utilizing a isokinetic dynamometer (83), was significantly correlated with team success (4) and high-intensity actions during football matches (83). Muscle strength differences were seen in level of play (professional > non-professional football players) (19), in different positions (attackers > defender > midfielders) (68, 90), starter vs. non-starter (48), and age (40, 53).
 

However, before we elaborate on the actual topic we would like to give some thoughts about the terminology that we are going to use in the text.

So far, we have used “strength training” for the actual term “resistance training” (which would be the “correct” term). Generally, strength training is a specific type of resistance training, as well as power and endurance training. As a result, resistance training can have the purpose to improve the strength, power or muscular endurance of the players. Depending on the goal of the resistance exercise, training needs to be appropriately.

In order to distinguish between those types of resistance training we would like to give the definitions:

Strength: the maximal force that a muscle group can generate at a specific velocity (50). It is very important in a sport that requires to lift/move an absolute weight (such as in rugby or American football). However, due to the fact that strength influences power it is important in performance measure (such as sprinting or jumping) and in later stages of rehabilitation after injury.

Power: Power is a product of force times velocity (the difference between strength and power is that power requires velocity of movement) (92). The importance of power can be seen in actions that require speed of movement (sprinting (14), change of direction, jumping (15), kicking). Generally, the greater the power developed in a specific movement the faster, greater, higher the outcome.

Endurance: describes how often a force can be produced against a given resistance. Football requires high muscular endurance as sprinting, kicking, jumping, change of direction are part of football and all actions need to be performed many times during training a game.

Therefore, training for each of the different form of resistance training has distinct characteristics that can be manipulated.

• Number of repetition
• Number of sets
• Amount of resistance (usually defined as %1RM (43))
• Duration of recovery between sets

The following will link the different types of resistance training to training guidelines/characteristics (the table is a conclusion of multiple references in (7)).

It needs to be stated that those characteristics/guidelines are influenced by training experience (beginner, intermediate, advanced), time of the season (off-season, pre-season, in-season) (7) and individual philosophy of the coach.

As it is evident and due to the amount of resistance used for different training goals there are some consequences for the training practice (and therefore exercises that might be performed “on-pitch” vs. exercises performed “gym-based”).

On-pitch exercises are usually performed with the purpose to:

• warm-up
• train muscular endurance (using body weight)
• train power (limited applicability)

Gym-based exercises are usually performed with the purpose to train:

• maximal strength
• power

Parts (muscles) of the body that should be trained for football are: legs, the core and part of the upper body, such as the shoulders.

Typical strength measures in football utilized isokinetic dynamometers investigating knee extensor and flexor concentric (12, 16, 19, 21, 23-27, 29, 30, 36-40, 46, 48, 53, 58-60, 67-69, 71, 73, 75, 81-87, 90, 95) and eccentric (21, 23, 25, 26, 29, 30, 36, 38-40, 46, 48, 58, 73, 81, 85, 86, 90, 95) and hip (71) strength, hamstring to quadriceps (16, 19, 21-23, 25, 26, 29, 30, 36-40, 44, 46, 48, 58, 59, 62, 68, 73, 84-86, 90, 95) and abductor to adductor (22) peak torque and rate of force development (36, 37) in dominant and non-dominant leg.

In addition, field tests, such as (half) back squat (4, 52, 56, 70, 77, 79, 94), leg extension (70), isometric (63) leg press (17, 70), leg curl (52, 70), step up (52) , bench press (17, 74, 94), hand grip strength (18) were also used to determine the strength of football players.

Improvements were seen in:

• strength (2, 3, 44, 51, 52, 63, 67, 70)
• speed (12, 15, 63, 79, 93)
• jump (17, 70, 79, 93)
  
• kicking (28, 31, 47, 64, 70, 93) and
• agility (89) performance
  

Length of training intervention:

• 4- (57)
  
• 6- (31, 44)
• 7- (77)
• 8- (56, 64, 89, 94)
• 10- (63, 67, 79)
• 11- (35)
• 12- (2, 93)
• 13- (52)
• 16- (17) weeks

Amount of training sessions per week:

• 2 (17, 56, 77, 79)
• 2-3 (17, 35, 57, 67)
• 3 (52, 63, 64, 70, 79)
• 3-4 (64, 77)
• 4 (44)

Training volume (Amount of sets per training session):

• 1-3 (70)
• 2-3 (67)
• 3-5 (35, 64)
• 3 (63, 93)
• 4 (52, 94) sets
  

Amount of repetition per set:

• 2-12 (70, 79)
• 6-12 (67, 93)
• 8-15 (17, 64)
  

Load per repetition:

• 70-80% (64)
• 40-85% (79)
• 55-80% (17)
• 50-95% (64, 70) of 1 RM or
• 3-4 (77)
• 6 (94)
• 3-8 (35, 52)
• 3-10 (79) repetition maximum

Duration of recovery between sets were: 

• 0.5 (93)
• 1 (77)
• 2 (35)
• 2-3 (17)
• 3 (94) minutes

However, no improvements in strength (88) or kicking performance (91) was also seen after strength training.

It is questioned from coaches many times when and how youth players can be trained for strength and power. In order to clarify some issues around this topic a first look needs to be taken at the “normal” development of strength and power in youth players with age.

Obviously with growth (and maturation) strength will develop in youth players. Especially around/close after PHV (PHV occurs in a “normal” white-western population around the age of 14 (8, 66)), the players will develop strength (and power) naturally (55). It is thought that due to maturation, the players’ ability to produce hormones facilitates muscle growth and therefore strength gains.

Furthermore and more specifically this point in time is believed to coincident with PWV (peak weight velocity) (11). Consequently, it seems that players are very sensitive to strength and power training around that time (12-18 month past PHV) (55).

However, this does not mean that strength and power development is linked to muscle growth only. Strength and power development results from a combination of muscular, neural and mechanical factors (1). Therefore, strength and power gains were observed in youth in a variety of developmental stages (9, 10).

So what does that mean? Obviously, strength and power gains can be achieved from an early age of the players’ development. However, especially close after PHV, rapid gains (and most likely the greatest training effects) in strength and power can be achieved, as changes were closely link to serum testosterone (41). Consequently, only the rate of development may differ between development stages (55) (pre- vs. mid- vs. post-PHV).

In order to load mid- and post-PHV players in different exercises, the correct techniques (of these exercises) need to be ensured beforehand. As a result, youth (especially pre- and mid-PHV) players need to master the exercises technically to avoid injuries.

The benefits of strength and power training were seen with regards to different performance measures (20), but also with regards to an injury prevention perspective (32) and programs were shown effective in female (42, 61) and male youth players (13, 15, 33-35, 45, 49, 72, 76, 80, 93).


Youth footballers benefited from the (strength/power (15) and complex (13)) training with improvements in sprint (15, 34, 35, 80), change of direction (49), jump (15, 34, 45, 93), and ball-shooting performance (93). The female youth players showed a reduced amount of injuries after neuromuscular training (42, 61).

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