Biomedical subjects

Poul Dyhre-Poulsen

Publications and source records attributed to Poul Dyhre-Poulsen.

10 recordsLinked to original sources

PubMed2006

The effect of handedness on electromyographic activity of human shoulder muscles during movement.

The aim of the study was to investigate whether there was a difference in the electromyographic (EMG) activity of human shoulder muscles between the dominant and nondominant side during movement and to explore whether a possible side-difference depends on the specific task. We compared the EMG activity with surface and intramuscular electrodes in eight muscles of both shoulders in 20 healthy subjects whose hand preference was evaluated using a standard questionnaire. EMG signals were recorded during abduction and external rotation. During abduction, the normalized EMG activity was significantly smaller on the dominant side compared to the nondominant side for all the muscles except for infraspinatus and lower trapezius (P <or= 0.002). In contrast, during external rotation, higher EMG activity was seen in the supraspinatus, infraspinatus, lower and upper trapezius and latissimus muscles of the dominant side (P <or= 0.01). We demonstrated a side-difference in shoulder muscle activity, which was dependent on the type of motion carried out, suggesting a qualitative difference in the activation of muscles during the two types of movement. Dynamic abduction has the characteristics of a dominant arm task (i.e., task performed almost exclusively by the dominant arm) and reduced muscle activity for the dominant side during abduction indicates a dominance-related advantage in arm dynamics.

Adult↗

PubMed2004

Reflexes in the shoulder muscles elicited from the human coracoacromial ligament.

Morphological studies have demonstrated mechanoreceptors in the capsuloligamentous structures of the shoulder joint, however knowledge of the role these joint receptors play in the control of shoulder stability is limited. We therefore investigated the effect of electrically induced afferent activity from mechanoreceptors in the coracoacromial ligament (CAL) on the activity of voluntary activated shoulder muscles in healthy humans. In study I, wire electrodes, for electrical stimulation, were inserted into the CAL in eight normal shoulders. In study II, a needle electrode was inserted into the CAL in seven normal shoulders. Electric activity was recorded from eight shoulder muscles by surface and intramuscular electrodes. During isometric contractions, electrical stimulation was applied to the CAL at two different stimulus intensities, a weak stimulus (stim-1) and a stronger stimulus (stim-2). In both experiments, electrical stimulation of the CAL elicited a general inhibition in the voluntary activated shoulder muscles. In study I the average latencies (mean+/-SE) of the muscular inhibition were 66+/-4 ms (stim-1) and 62+/-4 ms (stim-2) during isometric flexion and 73+/-3 ms (stim-1) and 73+/-5 ms (stim-2) during isometric extension. In study II the average latency (mean+/-SE) of the response was 66+/-4 ms (stim-1) during isometric flexion. Our results demonstrated a response, probably of reflex origin, from mechanoreceptors in the CAL to the shoulder muscles. The existence of this synaptic connection between mechanoreceptors in CAL and the shoulder muscles suggest a role of these receptors in muscle coordination and in the functional joint stability.

Adult↗

PubMed2003

Evaluation of the walking pattern in two types of patients with anterior cruciate ligament deficiency: copers and non-copers.

The purpose of the present study was to investigate whether different walking patterns in healthy subjects and in coper and non-coper subjects with deficient anterior cruciate ligaments could be quantified. An inverse dynamics approach was used to calculate joint kinematics and kinetics for flexion and extension. EMG signals of the hamstrings and quadriceps muscles were recorded. The results showed that the peak knee flexion angle was greater in the copers than in the controls. There was a positive correlation between the peak knee extensor moment and peak knee flexion angle. Furthermore, at a given peak knee flexion angle, the peak knee extensor moment was significantly larger in the controls than in the non-copers. The hip extensor moment in the copers was significantly larger than that of the non-copers and the controls. In conclusion, the three groups walked according to different patterns. It is suggested that the copers stabilized their knee joint by co-contraction of the hamstrings and quadriceps muscles, while the non-copers lacked this ability. Instead, the non-copers reduced the knee extensor moment in order to decrease anterior displacement of the tibia. The walking pattern differences observed between the copers and non-copers may explain their different post-injury activity levels.

Adaptation, Physiological↗

PubMed2002

H reflexes recorded during locomotion.

We recorded H reflexes and the biomechanics of movement during locomotion. The soleus H reflex was strongly modulated during normal walking, depressed during the swing phase and modulated with the EMG in the stance phase. The amplitude of the H reflex increased with the EMG activity and was larger during running than walking. There were individual differences in the modulation pattern covariant with the biomechanics of walking. Interpretation of the results requires knowledge of the method used and assessment of the stimulus and recording conditions.

Biomechanical Phenomena↗

PubMed2002

Differences in the movement pattern of a forward lunge in two types of anterior cruciate ligament deficient patients: copers and non-copers.

OBJECTIVE: To determine whether differences in the knee joint movement pattern of a forward lunge could be quantified in healthy subjects and in anterior cruciate ligament deficient subjects who were able to return to the same activity level as before their injury (copers) and in those who were not (non-copers). DESIGN: The movement patterns of the injured leg of the coper and non-coper anterior cruciate ligament deficient subjects and the right leg of the control subjects were compared statistically. BACKGROUND: The forward lunge seems to be a less stressful test than the commonly used one-legged hop test, which makes it a possible tool for evaluating and comparing the functional performance of non-copers and copers. METHODS: The movement pattern of a forward lunge was analysed by using a two-dimensional inverse dynamics method. The electromyographic activity of the quadriceps and hamstring muscles were recorded. RESULTS: The non-copers moved more slowly and loaded the knee joint less than the copers and controls. The copers moved more slowly during the knee flexion phase but as fast as the controls during the knee extension. The EMG results suggest that the copers stabilized their knee joint by increasing the co-contraction of the hamstrings during the extension phase. CONCLUSIONS: Differences between the three groups' movement patterns could be quantified. The forward lunge test seems appropriate to discriminate between the knee function in coper and non-coper anterior cruciate ligament deficient subjects. RELEVANCE: Information about the performance of movements, which significantly load the knee joint in coper and non-coper anterior cruciate ligament deficient patients may contribute to a better understanding of dynamic knee joint stabilization, which is relevant in relation to the development of rehabilitation strategies.

Adaptation, Physiological↗

PubMed2002

Cruciate ligament reflexes.

The idea of muscular reflexes elicited from sensory nerves of the cruciate ligaments is more than 100 years old, but the existence of such reflexes has not been proven until the recent two decades. First in animal experiments, a muscular excitation could be elicited in the hamstrings when the anterior cruciate ligament (ACL) was pulled, and tension in the ligament caused activity of the gamma motor neurones of the muscles around the knee. Impulses from the sensory nerves in ACL were activated during motion of the knee, in particular overstretching and combined extension and rotation. In humans, proprioception in the knee is decreased after ACL rupture. By mechanical or electrical stimulation of the ACL, an excitation in the hamstrings muscles can be elicited. During muscular activity, stimulation of the ACL or PCL results in a clear inhibition of the ongoing activity, both during static isometric and isokinetic muscle work, and also during dynamic activity (gait). This inhibitory reflex subjectively resembled giving way. The latency of the reflex was short in animals (about 3 ms) and long in humans (60-120 ms), probably caused by differences in the experimental setup and between species. The long latency in humans makes it unlikely that it is a directly protective reflex. Instead it may be involved in the updating of motor programs. Further research may characterize the reflex in details and map its pathways. The existence of this reflex indicate that the cruciate ligaments have an afferent function, which influences knee dynamics.

Animals↗

PubMed2002

Shoulder reflexes.

Dynamic shoulder stability is dependent on muscular coordination and sensory inputs. In the shoulder, mechanoreceptors are found in the coracoacromial ligament, the rotator cuff tendons, the musculotendinous junctions of the rotator cuff and in the capsule. The number of receptors in the capsule is small compared to the number in the other shoulder structures. Proprioceptive information from numerous receptors in muscles and tendons is mediated via fast conducting nervefibers and probably contribute more to kinaestethic sensation than information from capsule and ligaments. Therefore it seems likely that the joint receptors have a more distinct role for the kinaestethic sense than muscle receptors. In cats a direct reflex from the afferents innervating the shoulder to the muscles around the shoulder has been presented. The reflex had an extremely short latency (2.7-3.1 ms). In man, a very long latency (300 ms) excitatory reflex has been found when nerves in the capsule were stimulated electrically during shoulder surgery. In addition, when the anterior-inferior capsule was excited in conscious humans with modest amplitude electrical stimuli during muscle activity, a strong inhibition was found with an average latency of 33 ms. Stimulation of the sensory nerves in the coracoacromial ligament has also been found to modify muscle activity strongly. Even though our understanding of the control of shoulder motion is incomplete, it is clear that sensory inputs can strongly modify muscle activity around the shoulder. This has implications for rehabilitation and shoulder surgery.

Electric Stimulation↗

PubMed2002

Increased rate of force development and neural drive of human skeletal muscle following resistance training.

The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0-200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow ("neural drive") during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 +/- 9.8 to 339.0 +/- 10.2 N. m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 +/- 117 to 2,020 +/- 119 (P < 0.05), 1,802 +/- 121 to 2,201 +/- 106 (P < 0.01), 1,543 +/- 83 to 1,806 +/- 69 (P < 0.01), and 1,141 +/- 45 to 1,363 +/- 44 N. m. s(-1) (P < 0.01), respectively. Corresponding increases were observed in contractile impulse (P < 0.01-0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased (P < 0.01-0.05) 22-143% (mean average voltage) and 41-106% (rate of EMG rise) in the early contraction phase (0-200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.

Adult↗

PubMed2002

Neural adaptation to resistance training: changes in evoked V-wave and H-reflex responses.

Combined V-wave and Hoffmann (H) reflex measurements were performed during maximal muscle contraction to examine the neural adaptation mechanisms induced by resistance training. The H-reflex can be used to assess the excitability of spinal alpha-motoneurons, while also reflecting transmission efficiency (i.e., presynaptic inhibition) in Ia afferent synapses. Furthermore, the V-wave reflects the overall magnitude of efferent motor output from the alpha-motoneuron pool because of activation from descending central pathways. Fourteen male subjects participated in 14 wk of resistance training that involved heavy weight-lifting exercises for the muscles of the leg. Evoked V-wave, H-reflex, and maximal M-wave (M(max)) responses were recorded before and after training in the soleus muscle during maximal isometric ramp contractions. Maximal isometric, concentric, and eccentric muscle strength was measured by use of isokinetic dynamometry. V-wave amplitude increased approximately 50% with training (P < 0.01) from 3.19 +/- 0.43 to 4.86 +/- 0.43 mV, or from 0.308 +/- 0.048 to 0.478 +/- 0.034 when expressed relative to M(max) (+/- SE). H-reflex amplitude increased approximately 20% (P < 0.05) from 5.37 +/- 0.41 to 6.24 +/- 0.49 mV, or from 0.514 +/- 0.032 to 0.609 +/- 0.025 when normalized to M(max). In contrast, resting H-reflex amplitude remained unchanged with training (0.503 +/- 0.059 vs. 0.499 +/- 0.063). Likewise, no change occurred in M(max) (10.78 +/- 0.86 vs. 10.21 +/- 0.66 mV). Maximal muscle strength increased 23-30% (P < 0.05). In conclusion, increases in evoked V-wave and H-reflex responses were observed during maximal muscle contraction after resistance training. Collectively, the present data suggest that the increase in motoneuronal output induced by resistance training may comprise both supraspinal and spinal adaptation mechanisms (i.e., increased central motor drive, elevated motoneuron excitability, reduced presynaptic inhibition).

Adaptation, Physiological↗

PubMed2001

Interindividual differences in H reflex modulation during normal walking.

Based on previous studies, at least two different types of soleus Hoffmann (H) reflex modulation were likely to be found during normal human walking. Accordingly, the aim of the present study was to identify different patterns of modulation of the soleus H reflex and to examine whether or not subjects with different H reflex modulation would exhibit different walking mechanics and different EMG activity. Fifteen subjects walked across two force platforms at 4.5 km/h (+/-10%) while the movements were recorded on video. The soleus H reflex and EMG activity were recorded separately during treadmill walking at 4.5 km/h. Using a two-dimensional analysis joint angles, angular velocities, accelerations, linear velocities and accelerations were calculated, and net joint moments about the ankle, knee and hip joint were computed by inverse dynamics from the video and force plate data. Six subjects (group S) showed a suppressed H reflex during the swing phase, and 9 subjects (group LS) showed increasing reflex excitability during the swing phase. The plantar flexor dominated moment about the ankle joint was greater for group LS. In contrast, the extensor dominated moment about the knee joint was greater for the S group. The hip joint moment was similar for the groups. The EMG activity in the vastus lateralis and anterior tibial muscles was greater prior to heel strike for the S group. These data indicate that human walking exhibits at least two different motor patterns as evaluated by gating of afferent input to the spinal cord, by EMG activity and by walking mechanics. Increasing H reflex excitability during the swing phase appears to protect the subject against unexpected perturbations around heel strike by a facilitated stretch reflex in the triceps surae muscle. Alternatively, in subjects with a suppressed H reflex in the swing phase the knee joint extensors seem to form the primary protection around heel strike.

Adult↗