Do we need to think about connective tissues when strength training?

What are the connective tissues?

As far as the structures that contribute to movement are concerned, there are four main categories of connective tissue: (1) tendons, (2) intramuscular connective tissue, (3) ligaments, and (4) extramuscular connective tissue, which is often called “fascia,” although opinions on the terminology vary.

  • Intramuscular connective tissue contains muscle fibers, fascicles, and the whole muscle, and transmits forces from the muscle fibers throughout the muscle itself and ultimately to the tendon. There are three main layers of intramuscular connective tissue: (1) the endomysium, which surrounds each muscle fiber, (2) the perimysium, which surrounds each muscle fascicle (group of muscle fibers), and (3) the epimysium, which surrounds the muscle. These structures (especially the epimysium) are sometimes also grouped under the wider term “fascia” alongside the extramuscular tissues, which are very similar in nature.
  • Ligaments connect bones to one another. Their main role is to provide stability to the joint that they surround.
  • Extramuscular connective tissue (fascia) contains individual muscles, connects them together, and transmits forces between muscles, causing movements to occur in adjacent segments.

What are connective tissues made of?

Like muscles, connective tissues contain a great deal of water. For example, tendons are approximately 55–70% water. After removing water, however, all connective tissues are largely comprised of collagen.

How does connective tissue function during muscular contractions?

Each of the connective tissues (tendons, intramuscular connective tissue, ligaments, and extramuscular connective tissue) play important roles in muscular contractions. Since tendons work in series with the muscle, while the other tissues function in parallel, they behave more elastically and influence muscular function to a much more obvious degree.

#1. Tendons

Tendons connect the muscle to the skeleton. Originally, it was assumed that tendons were rigid links that acted merely to transmit tensile forces from the muscle to the bone. However, it has since become clear that tendons elongate a considerable amount when they are subjected to mechanical tension.

#2. Other connective tissues

The way in which the other connective tissues function during muscular contractions has been less well-studied. However, the research shows that, just like tendons, many of these structures (1) transmit forces between contracting muscle fibers and the skeleton, and (2) store elastic energy in muscular contractions.

How do connective tissues respond to endurance training?

When exposed to the repetitive but low forces that are common to endurance training, connective tissues respond by displaying fatigue damage. Fatigue damage is a materials science term and does not mean “fatigue” in the wider context of exercise science. It describes the process by which a structure degrades after being exposed to cyclical or constant loading.

How do connective tissues respond to strength training?

Each of the connective tissues (tendons, intramuscular connective tissue, ligaments, and extramuscular connective tissue) adapt to long-term training. However, since the tendons work in series with the muscle, while the other tissues function in parallel, their adaptations have different implications.

#1. Tendons

When exposed to sufficiently high forces, tendons adapt initially by becoming stiffer (increasing in Young’s modulus) and later by increasing in size (albeit only in the peripheral regions, as the central region does not increase in size after adolescence). Exactly why there is a disconnect in time between the adaptations in tendon stiffness and size is unclear.

#2. Other connective tissues

The way in which the other connective tissues respond to long-term strength training has not been well-studied. Even so, some research indicates that intramuscular collagen synthesis rates and expression are elevated after heavy strength training workouts, and intramuscular collagen content does seem to increase after long-term training programs. As for tendons, it is likely that the other connective tissues respond best to higher loads with sufficient rest periods between reps, and are more likely to display fatigue damage rather than beneficial adaptations when loads are lighter and loading cycles are more frequent.

How do connective tissues respond to plyometrics?

What are plyometrics?

Plyometrics are high-velocity movements that involve the SSC. Some coaches and researchers define plyometrics as any high-velocity movement that involves the SSC, while others include only a subset of such movements. One important subset of high-velocity movements that involve the SSC is the group of exercises that involve an impact that triggers the start of the eccentric phase. Examples of such exercises include the drop jump, bounding, hopping, and sprinting.

What are the adaptations to eccentric training?

Eccentric training causes large increases in eccentric strength and smaller (but still substantial) increases in maximum (concentric) strength. Eccentric training also differs from concentric and SSC strength training insofar as a large proportion of the muscle fiber growth that occurs is longitudinal rather than transverse.

What are the adaptations to high-velocity training?

High-velocity training causes large increases in high-velocity strength and smaller (but still substantial) increases in maximum (concentric) strength. When the loading used is conventional weight (and not isokinetic resistance) and there is no landing phase, there is little mechanical loading on the muscle fibers, and consequently minimal hypertrophy.

What are the known adaptations to plyometric training?

The adaptations that occur after plyometric training are not easy to predict and vary widely depending on the exact exercise used, since this affects the proportional amount of stimulus that arises from the eccentric and high-velocity phases of the movement.

How do connective tissues adapt to plyometric training?

We know that connective tissues (including muscle collagen and tendons) do adapt after plyometric training, most likely due to the eccentric loading that is experienced. This loading allows high forces to be experienced by the tissues, leading them to increase first in stiffness and later in size.

What are the practical implications?

For athletes

Athletes who perform rapid SSC movements (such as jumping, sprinting, and running while changing direction) will benefit greatly from using similar plyometrics in their training programs, to optimize the ratio of active muscle stiffness to tendon stiffness for SSC function in those movements. In contrast, overuse of heavy strength training or isometric training may have negative effects, because the ratio of active muscle stiffness to tendon stiffness will be altered such that the muscle must lengthen too far and too quickly during the SSC movements for it to produce force optimally.

For bodybuilders

Bodybuilders who use light loads exclusively may be at a greater risk of overuse injury to the connective tissues, owing to regular and sustained exposure to fatigue damage without the beneficial adaptations that occur after using moderate or heavy loads. Bodybuilders who prefer to use light loads may benefit from interspersing their customary training with regular training cycles of moderate or heavy loads to bring connective tissue stiffness and size to a level commensurate with their muscle size. When carrying out such cycles, using 3-second inter-rep rest periods may be optimal, as this will maximize tendon (and likely other connective tissue) adaptations.

What is the takeaway?

The connective tissues of the body (including the intramuscular and extramuscular connective tissues, tendons, and ligaments) contribute to muscular function and adapt after strength training and plyometrics. Understanding how and why these adaptations happen can help to reduce the risk of overuse injury and enhance performance.

Figuring out how strength training works. See more of what I do: https://www.patreon.com/join/SandCResearch

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