Biomedical subjects

S Peter Magnusson

Publications and source records attributed to S Peter Magnusson.

3 recordsLinked to original sources

PubMed2003

Region-specific differences in Achilles tendon cross-sectional area in runners and non-runners.

The present study examined the cross-sectional area (CSA) of the Achilles tendon in subjects who repeatedly exposed their tendons to large loads (habitual runners) compared to control subjects (non-runners). Six male habitual runners [36 (7) years, 70.9 (4.4) kg and 1.84 (0.05) m, +/-SD] who had performed distance running (approximately 80 km per week) for the last 5 years were compared to six non-runners [34 (3) years, 81.2 (8.7) kg and 1.81 (0.02) m, +/-SD]. Tendon CSA was obtained from MR images obtained with the ankle in a neutral position (90 degrees ). The most proximal aspect of the tuberosity of calcaneus was used as a landmark to standardize the levels of images: the most distal image (1) was obtained 10 mm above the proximal tuberosity of calcaneus, and the most proximal image (7) was obtained 70 mm above the proximal tuberosity of calcaneus. There was a significant difference in CSA along the length of the tendon both in runners ( P<0.001) and non-runners ( P<0.01). In non-runners and runners the CSA of the most distal part was 51% and 85% greater than the most proximal part of the tendon, respectively. Furthermore, there was a difference in tendon CSA between the groups, such that runners had a greater CSA (36%) than non-runners at the most distal part of the tendon ( P<0.05). The greater CSA in the distal tendon may reflect differences in structural properties along the length of the human Achilles tendon, while the greater CSA in runners compared to non-runners may indicate a region-specific hypertrophy in response to the habitual loading of running.

Achilles Tendon↗

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↗

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↗