Mattias Hedlund

Increased prefrontal activity and reduced motor cortex activity during imagined eccentric compared to concentric muscle actions.

In this study we used functional magnetic resonance imaging (fMRI) to examine differences in recruited brain regions during the concentric and the eccentric phase of an imagined maximum resistance training task of the elbow flexors in healthy young subjects. The results showed that during the eccentric phase, pre-frontal cortex (BA44) bilaterally was recruited when contrasted to the concentric phase. During the concentric phase, however, the motor and pre-motor cortex (BA 4/6) was recruited when contrasted to the eccentric phase. Interestingly, the brain activity of this region was reduced, when compared to the mean activity of the session, during the eccentric phase. Thus, the neural mechanisms governing imagined concentric and eccentric contractions appear to differ. We propose that the recruitment of the pre-frontal cortex is due to an increased demand of regulating force during the eccentric phase. Moreover, it is possible that the inability to fully activate a muscle during eccentric contractions may partly be explained by a reduction of activity in the motor and pre-motor cortex.

Insufficient loading in stroke subjects during conventional resistance training

Our objective was to assess the loading during a resistance-training task at a given training intensity in subjects with stroke and in healthy subjects. Subjects with stroke (n = 11) and two control groups (n = 11 in each) underwent strength measurements and a resistance-training task for elbow flexors. Torque and muscular activity obtained during the resistance-training task was related to values obtained during strength measurements. Even if relative loading throughout the concentric phase of the resistance-training task, expressed as percent of concentric isokinetic torque, was found to be similar among groups, we found indications of insufficient loading for the stroke group. Relative loading during the eccentric contraction phase, expressed as percent of eccentric isokinetic torque, was significantly lower for the stroke group. Also, when related to isometric maximum voluntary contraction, the loading was significantly lower for the stroke group, compared with the control groups, during the concentric and eccentric contraction phases. Furthermore, muscle activation during, as well as muscular fatigue after, the resistance-training task was somewhat lower for the stroke group. Hence, for subjects with stroke, the relative loading during resistance training, performed at a training intensity considered adequate for able-bodied, appears to be too low compared with the healthy controls.

Torque-angle relationship are better preserved during eccentric compared to concentric contractions in patients with stroke

The aim of this study was to compare the effect of isokinetic contraction mode and velocity on the torque-angle relationship during maximum voluntary elbow flexion in patients with stroke, age-matc ...

Is better preservation of eccentric strength after stroke due to altered prefrontal function

ABSTRACT Ventrolateral prefrontal cortex (VLPFC) is part of a network that exerts inhibitory control over the motor cortex (MC). Recently, we demonstrated that VLPFC was more activated during imagined maximum eccentric than during imagined concentric contractions in healthy participants. This was accompanied with lower activation levels within motor regions during imagined eccentric contractions. The aim was to test a novel hypothesis of an involvement of VLPFC in contraction mode-specific modulation of force. Functional magnetic resonance imaging was used to examine differences in VLPFC and motor regions during the concentric and the eccentric phases of imagined maximum contractions in a selected sample of subjects with stroke (n = 4). The subjects were included as they exhibited disturbed modulation of force. The previously demonstrated pattern within VLPFC was evident only on the contralesional hemisphere. On the ipsilesional hemisphere, the recruitment in VLPFC was similar for both modes of contractions. The findings support a hypothesis of the involvement of VLPFC in contraction mode-specific modulation of maximum force production. A disturbance of this system might underlie the lack of contraction mode-specific modulation commonly found among stroke subjects, often expressed as an increased ratio between eccentric and concentric strength.

The accuracy of using elastic resistance bands to evaluate muscular strength

Abstract Elastic resistance as a tool for evaluation of muscular strength has rarely been addressed even though it is commonly used in exercise and rehabilitation regimens involving the shoulder muscles. The aim was therefore to investigate the relationship and potential difference between development of force during maximal isokinetic (maximum peak force, maximum mean force and peak mean force) and elastic (one-repetition maximum (1 RM)) concentric shoulder flexion in healthy older adults. A total of 30 voluntary adults over the age of 50 (15 women, 15 men) were included. Intraclass correlation coefficient absolute agreement was 0.85, 0.43 and 0.48 for the isokinetic values respectively, when all subjects were analysed together. No difference was found between the isokinetic maximum peak force value and the elastic 1 RM for all participants (0.15 kg, p = 0.791), for men (0.80 kg, p = 0.121) or women (− 0.49 kg, p = 0.135). Variations at an individual level, i.e. 95% limits of agreement, were 3.3 kg for all participants, 2.8 kg for women and 3.2 kg for men. These results imply that elastic resistance could be used to evaluate shoulder flexion strength in both older men and women. However, the variation on an individual level and the lower agreement among women is important to consider.

Office-Cycling: A Promising Way to Raise Pain Thresholds and Increase Metabolism with Minimal Compromising of Work Performance

Aim Establishing the effects of low intensity cycling (LC), moderate intensity cycling (MC), and standing at a simulated office workstation on pain modulation, work performance, and metabolic expenditure. Methods 36 healthy adults (21 females), mean age 26.8 (SD 7.6) years, partook in this randomized 3 × 3 crossover trial with 75 minutes of LC on 20% of maximum aerobic power (MAP) output, 30 minutes of MC on 50% of MAP, and standing 30 minutes with 48-hour wash-out periods. Outcome measures were pain modulation (pressure pain threshold (PPT) and thermal pain threshold)), work performance (transcription, mouse pointing, and cognitive performance), and metabolic expenditure. Results PPTs increased in all conditions. PPT trapezius showed the highest increase after LC, 39.3 kilopascals (kPa) (15.6; 78.6), compared to MC, 17.0 kPa (2.8; 49.9), and standing, 16.8 kPa (−5.6; 39.4), p = 0.015. Transcription was reduced during LC and MC. Mouse pointing precision was best during standing and worst and slowest during MC. Cognitive performance did not differ between conditions. Metabolic expenditure rates were 1.4 (1.3; 1.7), 3.3 (2.3; 3.7), and 7.5 (5.8; 8.7) kcal/minute during standing, LC, and MC, respectively (p < 0.001). Conclusions LC seems to be the preferred option; it raised PPTs, more than doubled metabolic expenditure, whilst minimally influencing work performance.