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The effect of manual therapy techniques on the neuromuscular system
Dr. Eyal Lederman & Professor D. Newham


Neuromuscular activity underlies any physical event requiring skeletal muscle activation, such as during movement, posture and the musculo-skeletal aspect of behaviour and expression. This study examined whether neuromuscular activity could be altered from the periphery by the stimulation of mechanoreceptors during manual therapy. This has relevance for rehabilitation programmes aimed at modifying the activity of the neuromuscular system.
The excitability of the stretch reflex in the quadriceps, elicited by mechanical vibration, was used to assess motoneuron excitability following four types of manual interventions in six groups of normal subjects (n=180). The stretch reflex and motoneuron excitability were used for observing changes in activity across the whole reflex arc as an indication of viability of the system rather than a measure of the monosynaptic reflex per se. Surface electromyographic recordings were made during a background voluntary contraction at 10% maximal.  Manual techniques were classified according to their potential influence on motor processes. Two techniques were passive (static and dynamic), and thus only propriocetive feedback was available to the motor system, and two others were active (static and dynamic) involving voluntary muscle activity.
Only the active-dynamic technique produced a significant reduction of the stretch reflex amplitude (p<0.0001), which lasted for 0.5 minute following the cessation of the technique. Further studies showed that this change did not exceed the 0.5 minutes period. Increasing the repetition number of active-dynamic techniques did not alter the extent or duration of reduced excitability. A reduction of the stretch reflex amplitude was not observed when the background force of contraction was lowered. This led to the hypothesis that the observed reduced excitability may be related to 'central dampening' rather than a direct effect of the technique on motor neuron excitability.
Further studies were carried out to examine the influence of the manual techniques on subjects with long-term knee damage who displayed voluntary activation failure (n=9). This is a common condition in musculoskeletal management. Three manual techniques were investigated; two active and one passive. There were no significant differences between the amplitude of the stretch reflex in healthy subjects and those suffering from knee damage. No significant changes were found in the amplitude of the stretch reflex in response to the manual events. The application of the three forms of manipulation to the damaged knees did not produce a significant change in voluntary activation of the quadriceps.
These studies support a centralist view of neuromuscular rehabilitation. Any changes to the motor output may be related to motor learning processes that are centrally organised. For neurorehabilitation purposes, intervention apparently needs to be cognitive, volitional and repetitive. Single active episodes or passive techniques are unlikely to leave a long-term change on motor activity.

Effects of different types of manual techniques on short term balance ability
Dr. E. Lederman & John Dalkirn
   
The effects of different types of manual techniques on short-term balance ability were studied in a randomised, controlled study in healthy human subjects (n=44, x females y males ages range 19 to 47 yr). Single leg stance balance ability was measured before and after administration of different manual techniques to leg: Passive Static (PS) technique, consisting of massage to the whole of the test limb, Passive Dynamic (PD) technique, involving passive movement of the hip and knee, Active Static (AS) technique, which was in the form of isometric hip and knee extensions, Active Dynamic (AD) techniques, where the subjects produced dynamic hip and knee extensions and Challenged Balancing (CB) where the subject's balance was manually challenged. Statistical analysis (Wilcoxon Signed-Ranks Tests) demonstrated that all techniques were significantly different from the control (p=0.XX) except PS techniques (p=0.XX). There were also significant differences between techniques (, p<0.001) with a descending order of efficacy at improving short-term balance ability: CB, AD, AS, PD then PS. The physiological mechanisms to explain these findings are discussed. This study highlights a valuable clinical application for using appropriate manual techniques to improve balance ability.

Co-contraction of triceps during isometric activity in biceps brachii: implications to Muscle Energy Technique
Dr. E. Lederman & Marcus Vaz

There is a widespread, but unsubstantiated, belief in osteopathy that during MET the isometric contraction of agonists will reciprocally inhibit the antagonistic muscles. However, there is mounting evidence that during many motor activities there is co-contraction of both agonist and antagonist muscles. Co-contraction implies an absence of reciprocal inhibition and therefore raises the question whether MET can cause a drop in antagonistic neuromuscular activity.
The aim of the present study was to investigate the neuromuscular activity of antagonist muscle (triceps) during isometric contraction of the biceps brachii. If inhibition was present than it would have been expected the triceps EMG would remain at the amplitude of its resting state. An increase in the triceps EMG activity would imply that co-contraction has taken place rather than inhibition.
Surface electromyography (EMG) was used to study the neuromuscular activity of the antagonist muscles (triceps) during isometric biceps contraction in normal healthy subjects (N=30, males 15 and females 15). EMG activity of the left triceps was recorded during 25%, 50% and 75% of the maximum voluntary contraction (MVC) of the left biceps brachii. The objective was to observe whether the antagonist muscle was inhibited or whether it co-contracted. There were significant differences in mean area (MA), average amplitude (AA) and peak amplitude (PA) of triceps during biceps contractions.
a) During biceps 25% MVC triceps activity significantly increased (MA P<0.001; AA p<0.001; PA p<0.0001).
b) During biceps 50% MVC triceps activity significantly increased (MA p<0.001; AA p<0.001; PA p<0.0001).
c) During biceps 75% MVC triceps activity significantly increased (MA p<0.001; AA p<0.001; PA p<0.0001).
All subjects demonstrated co-contraction of triceps during 25%, 50% and 75% biceps brachii MVC. These data question the ability of muscle energy technique (MET) to produce reciprocal inhibition in antagonistic muscle.