This blogpost will focus on maximal muscle Strength and the role of fiber adaptations for maximal strength.

Disclosure: Muscle strength is influenced by many parameters, however we this blogpost can not over it all at once.

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Maximal muscle Strength is simply the maximal force develop by a muscle or a muscle group in a single maximal voluntary contraction (MVC) irrespectively of time.

Maximal strength training is often characterized by a lifted load using 1-5 repetition maximum (RM) testing, however, muscle strength is very depended on a person ability to activate the neuromuscular system and the intramuscular coordination specific to the muscle action (movement / isometric contraction).

Furthermore muscle strength can be measured in a isome-, concen-, eccentric action. 

  1. Isometric: applying force against an irremovable object
  2. Concentric: to overcome an external load (i.e. concentric muscle action) where the muscle shortening.
  3. Eccentric (yield) against an external load (i.e. eccentric muscle action) where force gets produced as the muscles lengthening which are critical for muscle adaption for both sports performance and injury prevention.

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Force velocity relationship (F-V)

Another way to assessing maximal strength is to consider the force velocity relationship as when the velocity of a muscle contraction decreases the muscle force will increasing.

Below you can see illustration of the F-V relationship where the vertical axes is the force and on the horisontal axes is the velocity of muscle shortening.

In a maximal isometric strength the velocity is 0. Eccentric strength have higher force than isometric strength as the velocity shortening is lower than 0 (because of eccentric movement) and the eccentric strength is roughly 40% higher than the isometric strength.

For example in a leg extension exercise the force you extending your knees with is an concentric force, then you can hold in a static isometric contraction, then you should be able to add load and control the eccentric movement down to starting position.

Skærmbillede 2019-04-06 kl. 23.33.42 Testing maximal strength

In reality testing true strength is difficult and lot of factors have to be taken into considerations, but is typically tested establish by the 1RM an athlete can lift one time with good technique. However, 1RM is very challenging with a higher risk of injury and requires considerable lifting experience. Beside, it is properly not relevant for most individuals in general populations.

Therefore, another option is to estimate 1RM by doing a 5RM using a predictable equation to calculate what your 1RM.

The advantaged of this is typically reduce of injuries, and the test is mostly done in a more familiar testing range. However, there is still limitation to this approach as it often overestimate 1RM for untrained or endurance trained individuals and can underestimate for stronger individuals.

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Muscle size

Another important factor for muscle force is the muscle size, and the muscle force is proportional to the physiological cross sectional area (PCSA) within the muscle fiber.

The adaption that occurs when PSCA increases is called hypertrophy. Hypertrophy means that the fiber muscle itself is getting bigger because of the increase of the muscle protein.

The muscle gets activated in a complex cellular signal pathways. One of these pathway is the mTOR which is a pathway that responds to mechanical stress which stimulates to protein syntheses. So to get the muscle to produce a higher force, we can get it bigger. The muscle size can be evaluated by Functional magnetic resonance imaging (fMRI) or using a DEXA scanner.

However, It is good to be aware of the time course of changes in muscle adaption. In the below to figure can you see the %-change in muscle architecture over days in strength training.

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Kubo, K., Ikebukuro, T., Yata, H., Tsunoda, N., & Kanehisa, H. (2010). Time Course of Changes in Muscle and Tendon Properties During Strength Training and Detraining. Journal of Strength and Conditioning Research,

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Seynnes OR, Early skeletal muscle hypertrophy and architectural changes in response to high-intensity resistance training,  2007

Loading parameters to train these strength abilities.

To get the right stimulation for muscle force, we often need to categorized the strength training in loading zones taken into consideration time under tension, type of adaption and other loading parameters reps, load % of 1RM, set, tempo and rest.

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