Ankle morphology amplifies calcaneus movement relative to triceps surae muscle shortening.

The present study investigated the mechanical role of the dorsoventral curvature of the Achilles tendon in the conversion of the shortening of the plantarflexor muscles into ankle joint rotation. Dynamic, sagittal-plane magnetic resonance spin-tagged images of the ankle joint were acquired in six healthy subjects during both passive and active plantarflexion movements driven by a magnetic resonance compatible servomotor-controlled foot-pedal device. Several points on these images were tracked to determine the 1) path and deformation of the Achilles tendon, 2) ankle's center of rotation, and 3) tendon moment arms. The degree of mechanical amplification of joint movement was calculated as the ratio of the displacements of the calcaneus and myotendinous junction. In plantarflexion, significant deflection of the Achilles tendon was evident in both the passive (165.7 ± 7.4°; 180° representing a straight tendon) and active trials (166.9 ± 8.8°). This bend in the dorsoventral direction acts to move the Achilles tendon closer to the ankle's center of rotation, resulting in an ∼5% reduction of moment arm length. Over the entire range of movement, the overall displacement of the calcaneus exceeded the displacement of the myotendinous junction by ∼37%, with the mechanical gains being smaller in dorsi- and larger in plantarflexed joint positions. This is the first study to assess noninvasively and in vivo using MRI the curvature of the Achilles tendon during both passive and active plantarflexion movements. The dorsoventral tendon curvature amplifies the shortening of the plantarflexor muscles, resulting in a greater displacement of the tendon's insertion into the calcaneus compared with its origin.

Relationship between quadriceps femoris muscle volume and muscle torque at least 18 months after anterior cruciate ligament reconstruction.

The purpose of this study was to evaluate motor unit recruitment in the quadriceps femoris (QF) after anterior cruciate ligament (ACL) rupture and repair. Subjects included 24 patients at ≥ 18 months after ACL reconstruction and 22 control subjects with no history of knee injury. A series of cross-sectional magnetic resonance images were obtained to compare the QF of patients' injured side with that of their uninjured sides and that of uninjured control subjects. Muscle torque per muscle volume was calculated as isokinetic peak torque divided by QF muscle volume (cm(3)). The mean muscle torque per unit volume of the injured side of patients was not significantly different from that of the uninjured side or control subjects (one-way ANOVA) Results of the present study were contrary to the results of a previous study that evaluated patients at ≤ 12 months after ACL reconstruction. The present study found that high-threshold motor unit recruitment was restored at ≥ 18 months after ACL reconstruction. Thus, clinicians must develop techniques that increase the recruitment of high-threshold motor units in the QF from the period immediately after the injury until approximately 18 months after ACL reconstruction.

Superficial cooling inhibits force loss in damaged muscle.

The purpose of the study was to determine the effect of muscle damage with and without superficial cooling on force and neural activation of the triceps surae muscles. Seven men performed maximal plantarflexion contractions with and without superficial cooling over the medial gastrocnemius, before, immediate after, and 2 days after transcutaneous electrical stimulation for the medial gastrocnemius, respectively. Transcutaneous electrical stimulation was used to induce muscle damage. The normalized value, which was expressed as percentages of the corresponding relative values obtained before transcutaneous electrical stimulation to after transcutaneous electrical stimulation, of peak torque and integrated electromyogram for the soleus were significantly greater with than without superficial cooling. There was a significant correlation in normalized integrated electromyogram between the medial gastrocnemius and soleus. We conclude that superficial cooling appears to have reduced the magnitude of force loss during maximal voluntary contraction following damage to one of the muscles and the synergistic muscle activation may have contributed to the better force maintenance. The implications of this study are that TES enables more selective damage of muscle than standard protocols, and that superficial cooling over a damaged muscle may have an important role in the acute treatment of muscle injuries.

Effects of vascular occlusion on maximal force, exercise-induced T2 changes, and EMG activities of quadriceps femoris muscles.

The purpose of our study was to determine the effect of vascular occlusion on neuromuscular activation and/or the energy metabolic characteristics of the quadriceps femoris (QF) muscles during muscle contractions. Seven men participated in the study. An occlusion cuff was attached to the proximal end of the right thigh, so that blood flow in the anterior medial malleolar artery was reduced to approximately 88 % of the non-occluded flow. Muscle functional magnetic resonance imaging and maximal voluntary contraction (MVC) were carried out before and immediately after 5 sets of 10 repetitions of knee extension exercises at 50 % of the 10 repetitions maximum, from which transverse relaxation times (T2) and maximal force were measured, respectively. Integrated electromyography (iEMG) activity was recorded from the belly of the rectus femoris, vastus lateralis, and vastus medialis muscles during MVC and repetitive exercises. The percentage change in T2 was significantly increased for individual QF muscles, and there was a significant increase in iEMG activity over the 5 sets of repetitive exercises under conditions of vascular occlusion, but there was no significant effect on isometric force and iEMG activity during MVC. These results are consistent with the idea that there is greater osmolite accumulation during exercise with occlusion, although increased neural activation cannot be ruled out.

The effects of ice application over the vastus medialis on the activity of quadriceps femoris assessed by muscle function magnetic resonance imaging.

AIM: The purpose of this study was to investigate the effect of ice application for the muscle vastus medialis (VM) on the activation pattern of the quadriceps femoris muscle during repetitive knee extensions using muscle function magnetic resonance imaging (mfMRI) technique. METHODS: Seven men underwent transverse relaxation time (T2)-weighted magnetic resonance imaging (spin echo, TR/TE=1500/25, 80 ms, 10 mm slice thickness and gap) of their right thigh at rest and immediately after isotonic knee extension exercise with 5 sets of 10 repetitions at a load equal to 70% of their 10 repetitions with and without skin cooling. Cooling over surface skin of the VM was carried out for 3 min before and during 60-s of each rest interval between the knee extension exercise. RESULTS: The relative change in T2 of the muscle vastus intermedius increased significantly more by skin cooling than the control (p<0.01), but not the muscle rectus femoris (RF), muscle vastus lateralis, and VM. CONCLUSION: These results suggest that selective skin cooling combined with repeated muscle contraction facilitates the activation of other synergistic muscles, making this technique useful for activating the agonist muscles expected for injured muscle in training and rehabilitation.

Recruitment of the thigh muscles during sprint cycling by muscle functional magnetic resonance imaging.

The purpose of the present study was to investigate recruitment patterns of the thigh muscles during maximal sprint cycling by muscle functional magnetic resonance imaging (mfMRI). Twelve healthy men participated in this study and performed 2, 5, and 10 sets of 6-s supramaximal cycling with a load of 7.5 % of their body weight with 0.5 min of rest between the sets. Before and immediately after the exercise, T2-weighted MR images, i.e. mfMRI, of the right-thigh were taken to calculate T2 of eleven thigh muscles. Vastus lateralis, semitendinosus, and sartorius were the highest activated, i. e. had the greatest T2 change, among the quadriceps, hamstring, and adductors, respectively, compared with other muscles. Total power output during 2, 5, and 10 sets of sprint cycling was correlated with percent change in T2 in the quadriceps correlated (r (2) = 0.507 to 0.696, p < 0.01), the hamstring (r (2) = 0.162 to 0.335, p < 0.05 approximately 0.001), and the adductor muscles (r (2) = 0.162 to 0.473, p < 0.05 approximately 0.0001). With use of stepwise regression analysis, total power output was significantly correlated with % change in T2 of the vastus medialis (VM) (p < 0.0001) and vastus intermedius (VI) (p < 0.05) (r (2) = 0.698, p < 0.0001). We concluded that eleven thigh muscles were activated non-uniformly, and that the VM and VI play a key role during maximal sprint cycling.