Biomedical subjects

Per Aagaard

Publications and source records attributed to Per Aagaard.

7 recordsLinked to original sources

PubMed2003

Increased cross-sectional area and reduced tensile stress of the Achilles tendon in elderly compared with young women.

The Achilles tendon cross-sectional area (CSA), tensile force, and stress during an isometric contraction were examined in healthy young (n = 9, age = 29 +/- 1 years, mean +/- SEM) and elderly (n = 10, 79 +/- 2 years) women. CSA area was obtained with magnetic resonance imaging 3 cm proximal to the insertion, and tendon force was obtained from the isometric ankle moment. The moment of force about the ankle joint was greater in young women (95 +/- 17 N m) than in elderly women (51 +/- 5 N m; p <.05). The Achilles tendon CSA was significantly greater in elderly women (56.3 +/- 3.0 mm(2)) than in young women (46.0 +/- 1.9 mm(2); p <.01). These data show that young women can exert a greater force than elderly women on the Achilles tendon during voluntary contraction, although elderly women have an increased (22%) tendon CSA, and a lower tendon force than young women. The greater tendon size combines to lower the stress on the tendon markedly, which may reduce the risk of injury to the tendon.

Achilles Tendon↗

PubMed2003

Training-induced changes in neural function.

Adaptive changes can occur in the nervous system in response to training. Electromyography studies have indicated adaptation mechanisms that may contribute to an increased efferent neuronal outflow with training, including increases in maximal firing frequency, increased excitability and decreased presynaptic inhibition of spinal motor neurons, and downregulation of inhibitory pathways.

Adaptation, Physiological↗

PubMed2002

Flow paths in wetting unsaturated flow: experiments and simulations.

The flow paths and instabilities of gravity driven infiltration of a wetting fluid into a porous medium are studied. The model experiments and simulations independently represent techniques to study the unsaturated flow in porous media, and they produce a consistent picture of how the paths of fluid transport form and depend on the relative strength of the gravitational force. The experiments, which employ a transparent and quasi-two-dimensional model, reveal that the fluid pathways contain an internal link-blob structure and increase in width with decreasing gravity. The model, which couples the well established invasion percolation model for capillary governed flow with a model that describes the viscous film flow in partially filled pores, corroborates these experimental findings.

Journal Article↗

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↗

PubMedDate not supplied

Transport and degradation of toluene and o-xylene in an unsaturated soil with dipping sedimentary layers.

A lysimeter trench was established at the Gardermoen delta (50 km north of Oslo, Norway) to study the flow of water and transport and degradation of aromatic jet fuel components (toluene and o-xylene) in the undisturbed unsaturated zone. Site investigations with ground-penetrating radar revealed the presence of dipping sedimentary layers within the foreset unit. This study has shown that the foreset bed of the Gardermoen delta structure provided a preferential flow path for the transport of the solute plumes, but did not have dramatic effects on the degradation potential under the current conditions. The degradation potential for toluene and o-xylene in the unsaturated zone at Gardermoen was very high and almost all of the injected hydrocarbons were biodegraded before reaching the saturated zone. However, the horizontal displacement of the plume showed that knowledge about sedimentary structures in the unsaturated zone is important for a sufficient monitoring of contaminant transport and for remediation purposes. Carbon dioxide and O2 were measured in situ simultaneously with extraction of water samples, and indicated aerobic biodegradation of toluene and o-xylene. Overall, first-order degradation coefficients were calculated to be in the range of 0.19 to 0.21 d(-1) and 0.10 to 0.11 d(-1) for toluene and o-xylene, respectively.

Bacteria, Aerobic↗