Astrid M. Horstman

Intrinsic muscle strength and voluntary activation of both lower limbs and functional performance after stroke.

The objective of this study was to assess the nature of muscle weakness in both legs after stroke compared with able‐bodied control individuals and to examine whether there is a relationship between the degree of muscle weakness and coactivation of knee extensors and flexors as well as voluntary activation capacity of knee extensors of both paretic and non‐paretic legs and indices of functional performance. Maximal voluntary isometric torques of knee extensors (MVCe) and flexors (MVCf) were determined in 14 patients (bilaterally) and 12 able‐bodied controls. Simultaneous measurements were made of torque and surface EMG from agonist and antagonist muscles. Coactivation was calculated. Supramaximal triplets were evoked with electrical stimulation to estimate maximal torque capacity and degree of voluntary activation of knee extensors. MVCs, activation and coactivation parameters were correlated to scores of seven functional performance tests. MVCe, MVCf and voluntary activation were lower in paretic lower limb (PL) compared with both non‐paretic lower limb (NL) and control. Besides, all these parameters of NL were also lower than control. Electrically evoked torque capacity of knee extensors of PL was about 60% of both NL and control, which were not significantly different from each other. Strong significant correlations between strength, as well as voluntary activation, and functional performance were found. Coactivation did not correlate well with functional performance. Thus, whereas for NL activation failure can explain weakness, for PL both activation failure and reduced intrinsic torque capacity are responsible for the severe weakness. Activation capacity and muscle strength correlated strongly to functional performance, while coactivation did not.

Biophysical aspects of submaximal hand cycling

Hand cycling is a popular form of wheeled mobility. This study evaluates biophysical differences between synchronous/asynchronous hand cycling. During submaximal hand cycling on a motor driven treadmill, 9 able-bodied subjects performed 2 series of 4 steady state exercise bouts at 1.11 to 2.78 m/s. Metabolic parameters, mean force on the handle bar, muscle activity and local perceived exertion in the upper body were determined. Mean power output was 35.4 +/- 7 W (v = 2.78 m/s). At this speed oxygen uptake was 1.11 +/- 0.25 and 1.26 +/- 0.26 l/min for the synchronous and asynchronous modes, respectively. Mechanical efficiency was significantly higher (v = 2.78 m/s: + 11.5 %) in synchronous cycling. Higher activity of m. obliquus externus and extensor carpi ulnaris was seen. Mean 2D total force and fraction effective force on the handle bar were lower in asynchronous hand cycling. Local perceived discomfort was higher in the asynchronous mode for different arm regions. Synchronous hand cycling is more efficient and at a lower metabolic cost. Mean muscle activation and the local perceived discomfort may explain some results. Future study should focus on combined time-based force and muscle activity characteristics. Synchronous hand cycling should be preferred during submaximal exercise in early rehabilitation.

Influence of vibration resistance training on knee extensor and plantar flexor size, strength, and contractile speed characteristics after 60 days of bed rest.

Spaceflight and bed rest (BR) result in loss of muscle mass and strength. This study evaluated the effectiveness of resistance training and vibration-augmented resistance training to preserve thigh (quadriceps femoris) and calf (triceps surae) muscle cross-sectional area (CSA), isometric maximal voluntary contraction (MVC), isometric contractile speed, and neural activation (electromyogram) during 60 days of BR. Male subjects participating in the second Berlin Bed Rest Study underwent BR only [control (CTR), n = 9], BR with resistance training (RE; n = 7), or BR with vibration-augmented resistance training (RVE; n = 7). Training was performed three times per week. Thigh CSA and MVC torque decreased by 13.5 and 21.3%, respectively, for CTR (both P < 0.001), but were preserved for RE and RVE. Calf CSA declined for all groups, but more so (P < 0.001) for CTR (23.8%) than for RE (10.7%) and RVE (11.0%). Loss in calf MVC torque was greater (P < 0.05) for CTR (24.9%) than for RVE (12.3%), but not different from RE (14.8%). Neural activation at MVC remained unchanged in all groups. For indexes related to rate of torque development, countermeasure subjects were pooled into one resistance training group (RT, n = 14). Thigh maximal rate of torque development (MRTD) and contractile impulse remained unaltered for CTR, but MRTD decreased 16% for RT. Calf MRTD remained unaltered for both groups, whereas contractile impulse increased across groups (28.8%), despite suppression in peak electromyogram (12.1%). In conclusion, vibration exposure did not enhance the efficacy of resistance training to preserve thigh and calf neuromuscular function during BR, although sample size issues may have played a role. The exercise regimen maintained thigh size and MVC strength, but promoted a loss in contractile speed. Whereas contractile speed improved for the calf, the exercise regimen only partially preserved calf size and MVC strength. Modification of the exercise regimen seems warranted.

Intrinsic properties of the knee extensor muscles after subacute stroke.

UNLABELLED Horstman AM, Gerrits KH, Beltman MJ, Koppe PA, Janssen, TW, de Haan A. Intrinsic properties of the knee extensor muscles after subacute stroke. OBJECTIVE To characterize muscle properties of paretic lower-limb (PL) and nonparetic lower-limb (NL) knee extensors in patients with subacute stroke. DESIGN Case-control study. SETTING Rehabilitation center research laboratory. PARTICIPANTS Patients with subacute stroke (n=14) and able-bodied age-matched control subjects (n=12). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Half relaxation times (HRTs) and maximal rates of torque development (MRTDs) were assessed as indicators of contractile speed using both voluntary and electrically evoked contractions. Moreover, changes in torque were measured during a fatigue protocol (35 electrically evoked intermittent contractions; 1.5s on, 2s off) and recovery. RESULTS No differences among groups were found for normalized MRTDs during electrically evoked contractions (P=.117). However, during voluntary contractions both PLs (53% of control, P=.022) and NL (71% of control, P<.001) had significantly lower MRTD compared with control. Both PL (134% of control, P=.001) and NL (123% of control, P=.032) had significantly higher HRTs than control, indicating muscle slowing in patients with subacute stroke. PLs fatigued more and faster than control (P=.011) and both PL and NL recovered slower (P<.001). CONCLUSIONS The changes in HRTs and fatigue suggest adaptations in muscle properties toward slower, more fatigable muscle shortly after stroke. The inability to make use of contractile speed because of impaired neural activation seems the most limiting factor during the initial phase of torque development in PL. Thus, besides strengthening, muscle endurance and speed should also be addressed during rehabilitation.

Increased H-reflex excitability is not accompanied by changes in neural drive following 24 days of unilateral lower limb suspension.

The purpose of this study was to determine whether the gain in soleus H‐reflex excitability induced by unilateral lower limb suspension (ULLS) is associated with changes in neural drive to the plantar flexor muscles. Six male subjects (23 ± 2 years, 187 ± 7 cm, 79 ± 9 kg) underwent 24 days of ULLS of the dominant limb. Plantar flexor maximal voluntary contraction (MVC) torque, activation capacity (twitch interpolation), soleus maximal electromyographic (EMG) activity, Hoffman (H)‐reflex, and the first volitional (V) wave normalized to the compound muscle action potential (M‐wave) were quantified before and after ULLS. Following ULLS, MVC torque decreased by 15% (P < 0.05). However, neither activation capacity nor EMG activity was significantly altered after the suspension. The V‐wave remained unchanged consistently after ULLS, whereas the H‐reflex increased significantly (+20%). Furthermore, there was no significant relationship between changes in H‐reflex and V‐wave over the ULLS period. These findings indicate that 24 days of ULLS can result in a substantial reduction of muscle strength without any apparent change in voluntary activation capacity. H‐reflex and V‐wave findings suggest that the spinal adaptations that underlie the unloading‐induced increase in resting soleus H‐reflex excitability did not significantly affect the efferent motor output to the plantar flexor muscles. Muscle Nerve, 2009

The identification of genetic pathways involved in vascular adaptations after physical deconditioning versus exercise training in humans

•  What is the central question of this study? The aim of this study is to identify genes that are involved in vascular adaptations after physical deconditioning and exercise training in humans. •  What is the main finding and its importance? Using unique human in vivo models for local deconditioning and exercise training, we demonstrate that the vascular endothelial growth factor signalling pathway, regulation through transforming growth factor β1 and extracellular matrix‐related genes are likely to be involved in vascular adaptations after physical (in)activity.

Leucine Supplementation Does Not Attenuate Skeletal Muscle Loss during Leg Immobilization in Healthy, Young Men

Background: Short successive periods of physical inactivity occur throughout life and contribute considerably to the age-related loss of skeletal muscle mass. The maintenance of muscle mass during brief periods of disuse is required to prevent functional decline and maintain metabolic health. Objective: To assess whether daily leucine supplementation during a short period of disuse can attenuate subsequent muscle loss in vivo in humans. Methods: Thirty healthy (22 ± 1 y) young males were exposed to a 7-day unilateral knee immobilization intervention by means of a full leg cast with (LEU, n = 15) or without (CON, n = 15) daily leucine supplementation (2.5 g leucine, three times daily). Prior to and directly after immobilization, quadriceps muscle cross-sectional area (computed tomography (CT) scan) and leg strength (one-repetition maximum (1-RM)) were assessed. Furthermore, muscle biopsies were taken in both groups before and after immobilization to assess changes in type I and type II muscle fiber CSA. Results: Quadriceps muscle cross-sectional area (CSA) declined in the CON and LEU groups (p < 0.01), with no differences between the two groups (from 7712 ± 324 to 7287 ± 305 mm2 and from 7643 ± 317 to 7164 ± 328 mm2; p = 0.61, respectively). Leg muscle strength decreased from 56 ± 4 to 53 ± 4 kg in the CON group and from 63 ± 3 to 55 ± 2 kg in the LEU group (main effect of time p < 0.01), with no differences between the groups (p = 0.052). Type I and II muscle fiber size did not change significantly over time, in both groups (p > 0.05). Conclusions: Free leucine supplementation with each of the three main meals (7.5 g/d) does not attenuate the decline of muscle mass and strength during a 7-day limb immobilization intervention.

Enhanced physiological tremor deteriorates plantar flexor torque steadiness after bed rest

This study evaluated the effectiveness of resistance training to preserve submaximal plantar flexor (PF) torque steadiness following 60 days of bed rest (BR). Twenty-two healthy male subjects underwent either BR only (CTR, n=8), or BR plus resistance training (RT, n=14). The magnitude of torque fluctuations during steady submaximal isometric PF contractions (20%, 40%, 60% and 80% of maximum) were assessed before and after BR. Across contraction intensities, torque fluctuations (coefficient of variation, CV) increased more (P<0.05) after BR for CTR (from 0.31±0.10 to 0.92±0.63; P<0.001), than for RT (from 0.30±0.09 to 0.54±0.27; P<0.01). A shift in the spectral content of torque fluctuations towards increased rhythmic activity between 6.5 and 20Hz was observed in CTR only (P<0.05). H-reflex amplitude (H(max)/M(max) ratio) declined across groups from 0.57±0.18 before BR to 0.44±0.14 following BR (P<0.01) without correlation to CV. The present study showed that increased torque fluctuation after BR resulted from enhanced physiological tremor. Resistance training prevented the spectral shift in isometric PF torque fluctuation and offset ∼50% of the decline in performance associated with long-term BR.

Muscle properties and functional recovery until one year after stroke

Purpose: to investigate functional performance in relation to muscle function during first year after stroke. Methods: Maximal voluntary isometric torques of knee extensors (MVTe) and flexors (MVTf) were obtained in 14 patients with subacute stroke (bilaterally) 3.5±2 months after stroke and 3 (n=8), 6 (n=5) and 12 months (n=3) thereafter and in 12 age-matched able-bodied subjects. Maximal triplet response (intrinsic muscle strength), maximal rate of torque development (MRTD) and degree of voluntary activation of knee extensors were estimated. Patients performed 7 tests of functional performance. Results: In the paretic lower limb (PL), all parameters significantly (0.494<|r|<0.909) improved during all follow-ups. In the non-paretic lower limb (NL) most improvement occurred within the first 3 months. For NL and PL, MVTe improved 5 and 16%, respectively MVTf 3 and 20%, triplet 0 and 13%, activation 8 and 9%, MRTD 16 and 61%. Significant correlations (0.460<|r|<0.906) were found between all tests of functional performance and all muscle parameters of PL and all parameters (0.454<|r|<0.873) but triplet and MRTD of NL. Conclusion: All strength parameters correlated significantly with functional performance. Therefore, it is recommended to investigate the role of strength training of both legs during at least the first year of stroke.