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controller” to coordinate the necessary trunk muscles for stabilizing the spinal column is stressed.
Regarding the trunk muscles activation patterns, it was showed that local and global muscles are
affected in an opposite manner in the presence of LBP (Hodges, 2004). Global muscles control
intervertebral motion only by augmented activations, resulting in co-contractions, higher spine
loads and reduced normal movement of the spine (Hodges, 2004). Therefore, the activity of the
global muscles was used as a measurable compensation for poor passive or active (local muscles)
segmental support (Cholewicki, Panjabi, and Khachatryan, 1997).
1.5.3.2.
Muscle Function Disruption
LBP related to the muscle function disruption is well documented to the scientific literature,
however, the question is what kind of disorders can effect back muscles (Bogduk, 2005). Bogduk
(2005), postulated that there is a lack of direct evidence of the responsible lesion. Therefore,
(A) according to the “Cinderella” hypothesis there are low-threshold motor units (type I) that are
always recruited as soon as the muscle is activated and stay active until total muscular relaxation
face energy crisis at the membrane level, which may lead to degenerative processes, necrosis,
and pain (Hagg, 2000). If the load condition remains the same, the next motor units on the
recruitment pyramid get affected (Henneman, Somjen, and Carpenter, 1965). Localized muscle
fatigue can also occur in low-level long-lasting static contractions where the “Cinderella” fibers are
always recruited (Hagg, 2000; NRC-IOM, 2001; Radwin, Marras, and Lavender, 2002; Sjogaard,
1985; Sjogaard and Jensen, 2006). (B) Constant muscle tension can decrease blood flow and
oxygenation in muscles and its nerves resulting in ischaemic muscle pain (Bogduk, 2005; Marras,
2008). (C) Myofascial trigger points represent areas of hypercontracted muscle cells that deplete
local energy stores and impair the function of calcium pumps, thereby perpetuating the contraction.
Pain is said to occur as a result of obstruction of local blood flow and the accumulation of algogenic
metabolites such as bradykinin. Myofascial trigger points are believed to arise as a result of acute
or chronic repetitive strain of the affected muscle or ’reflexily’ as a result of underlying joint disease
(Bogduk, 2005; Marras, 2008). (D) In eccentric contractions the mechanical load that is applied
on the muscle exceeds the force developed by the muscle. The muscle is doing negative work
and absorbs mechanical energy. The use of the absorbed energy is task depended. Therefore, it
can be dissipated as heat, in which case the muscle is functioning as a damper and attenuates
impact forces, or the energy is recovered at the concentric phase of the stretch-shortening cycle,
hence potentiates the power output. Muscle strain injuries occur as a response to excessive load
or stretch and are most common during eccentric contractions in muscles that span two or more
joints. Workplace factors like repetition, range of motion, work-rest cycle, and age influence effects
the susceptibility of injuries (Bogduk, 2005; Cutlip et al., 2009; Marras, 2008; Roy and DeLuca,
1996).
1.5.4.
Theories for MSD Causation
Kumar (2001), proposed four models about the development of MSD, where he took into consideration that localized muscle fatigue can provoke either fatigue of motor units or skeletal
fiber damage. Regarding the latter, fatigue may decrease the tolerance to stress and therefore
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