Connective Tissue Sheaths
Weight training may strengthen the sheaths of connective tissue
within and around the muscle by increasing their collagen content.
These connective tissues sheaths provide the framework that supports
muscle overload and are the main component in the tensile strength
and passive viscoclastic properties of muscle.
- endomysium surrounds individual fibers
- perimysium encloses groups of muscle fibers
- epimysium surrounds the entire muscle
Bone
Tensile strength and elasticity of bones decrease about 2%
per decade from age 20 to 90 years (Hayes, 1986).
Bone is only one fifth the weight of steel but can withstand
two times the compression force as granite, or four times the
compression force as concrete.
Weight bearing activities such as walking can prevent bone
mineral loss. Weight resistive exercises can prevent bone mineral
loss if the antigravity musculature is activated.
In animal studies, the first 40 repetitions of an exercise
stimulates greater than 95% of bone formation. Additional repetitions
do not significantly increase bone formation (Riewald S. Bone
of Contention: What Exercises Increase Bone Strength? Strength
and Conditioning Journal. 26, 1, pg 46-47.).
Astronauts have about the same rate of bone loss as those
on bed rest: about one percent per month.
Joint Cartilage
Resistance training can thicken the hyaline cartilage on the
articular surfaces of the bone (Ingelmark & Elsholm 1948).
Joint cartilage depends on synovial fluid for its nutrition
since it has no vascularization. Synovial fluid is forced into
the cartilage surfaces when the joint is loaded, as in physical
activity. Joint cartilage functions in an elastic manner during
short term loading. The cartilage becomes temporarily deformed
when long term loading forces water out of the cartilage. It
returns to its original shape after cessation of loading when
water is again drawn into the cartilage. The alternate compression
and decompression along with the pumping of synovial fluid due
to physical activity is partly responsible for nutrition to the
cartilage.
Tendon and Ligament
Resistance training can increase the size and strength of
tendons and ligaments (Fahey et al. 1975). This may be due to
an increase of collagen within the connective tissue sheaths
(Laurent et al. 1978).
The elastic limit of a tendon or ligament can be enhanced
by exercise and training and can be reduced by aging and inactivity.
The elastic limits of ligament are estimated to be 12-50%, and
the elastic limits of tendon is 9-30% (Weakest at MTJ).
Junction strength failure of a bone-ligament preparation occurs
at the attachment site of the ligament. The Junction strength
failure is similar in a bone-tendon-muscle-tendon-bone preparation
although separation may also occur at the muscletendinous junction
or in the muscle itself.
Research using animal models demonstrate that junction strength
of ligaments increases with endurance-type physical activity
and decreases with immobilization. Furthermore, damaged ligaments
regain strength faster if physical activity is performed afterwards.
Martin Paul, B.Sc. Kin., PFLC
writes:
An In Vitro setting, a ligament can stretch quite a bit. The
only ligament that can match the 50% elasticity is the ligamentum
flavum. Even then, Nachemson & Evans (1968) reported,
"Beyond this point, the stiffness increases greatly with
additional loading and the ligament failed abruptly (reached
Pmax) with little deformation. Furthermore, Butler et al (1978),
observed that beyond 4%, "small force reductions (dips)
can sometimes be observed in the loading curves for both tendons
and ligaments. These dips are caused by the early sequential
failure of a few greatly stretched fiber bundles. When sequential
failure occurs, it compromises the strength of the ligaments
and thus increases the instability of that particular joint.
Fung (1981), goes on to add that the upper limit for physiological
strain in tendons and ligaments is from 2 to 5%. Finally, Kear
& Smith (1975) findings suggest that "normal activity
a tendon in vivo is subjected to less than one fourth of its
ultimate stress."
- Butler, D.L., Groods, E.S., and Noyes, F. R.: Biomechanics
of Ligaments and Tendons. Exerc. Sport Sci. Rev., 6:125, 1978.
- Fung, Y.C.B.: Biomechanics: Mechanical Properties of Living
Tissues. NewYork, Springer Verlag, 1981, p.222.
- Kear, M., and Smith, R.N.: A method for recording tendons
strain in sheep during locomotion. Acta Orthop. Scand., 46:896,
1975.
- Nachemson, A.L., and Evans, J.H.: Some mechanical properties
of the third human lumbar interlaminar ligament (ligamentum flavum).
J. Biomech., 1:211, 1968.
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