The effect of unstable loading versus unstable support conditions on spine rotational stiffness and spine stability during repetitive lifting

The effect of different ranges of motion on local dynamic stability of the elbow during unloaded repetitive flexion–extension movements

“…This has been seen previously, where increases in lumbar spine muscle stiffness were observed in response to decreases in the stability of the external environment, while LDS was maintained at consistent levels (Beaudette et al, 2014). However, Beaudette et al (2014) examined a more challenging externally loaded lifting movement.…”

“…This has been seen previously, where increases in lumbar spine muscle stiffness were observed in response to decreases in the stability of the external environment, while LDS was maintained at consistent levels (Beaudette et al, 2014). However, Beaudette et al (2014) examined a more challenging externally loaded lifting movement. The unloaded repetitive elbow movements examined in the current study may not have been challenging enough to enable a thorough assessment of the body's response to kinematic perturbations and neuromuscular control errors.…”

“…2E) so that the co-contraction index was still close to 50%. Co-contraction is known to provide mechanical stability to a system (Granata & Marras, 2000), and active muscle stiffening, which can be related to co-contraction, is thought to play a role in local dynamic stability of the lumbar spine (Beaudette et al, 2014;Graham & Brown, 2012). However, the magnitude of co-contraction, as computed here, approaches 50% by creating a more balanced level of activation between the flexor and extensor muscles; less than 50% signifies a larger flexor activation, while greater than 50% signifies greater extensor activation.…”

“…Stability about a dynamically rotating joint can be defined as the ability to maintain an equilibrium, or intended trajectory, when confronted with small kinematic disturbances or neuromuscular control errors (England & Granata, 2007;Granata & England, 2006;Reeves et al, 2007). This capability is provided primarily by the active recruitment of muscles by the central nervous system (CNS) (Beaudette, Graham, & Brown, 2014;Granata & England, 2006).…”

“…LDS has also been investigated with respect to lumbar spine motion in response to changes in movement rate (Graham & Brown, 2012;Granata & England, 2006) and load (Graham & Brown, 2012), and correlated to muscle contributions in the form of trunk stiffness (Graham & Brown, 2012;Beaudette et al, 2014). However, the effect of range of motion (ROM), in terms of both magnitude (length of the target trajectory) and location (mid/end-range), has not been examined in relation to LDS.…”