Mark E. T. Willems

Heterogeneity of mean sarcomere length in different fibres: effects on length range of active force production in rat muscle

Isometric active length-force characteristics of rat semimembranosus lateralis muscles [rats,n = 6, body mass = 292 (SD 9) g] were recorded. Muscles were photographed during the force plateaus of the tetani to determine lengths of proximal, intermediate and distal fibres. From the mean number of sarcomeres in series in those fibres, mean sarcomere length at different muscle lengths was calculated. The heterogeneity of mean sarcomere lengths for each muscle was quantified according to the coefficient of variation of sarcomere lengths at muscle optimal length. Absolute muscle length changes were equal to fibre length changes. At all muscle lengths, mean sarcomere lengths in the distal fibres were significantly greater than those in proximal and intermediate fibres. The heterogeneity of mean sarcomere lengths augmented the length range of active force production between muscle optimal length and active slack length by about 38% to 43%. We concluded that in a muscle with a low degree of pennation, the heterogeneity of mean sarcomere lengths should be considered as a substantial contributor to the length range over which active force can be produced. In our experiment, the length ranges of active force production between optimal and slack length showed considerable differences (range 18.7–24.9 mm). The coefficient of correlation between length ranges and mean number of sarcomeres in series in various muscle regions was extremely low (r = −0.14) and not significant. The coefficient of correlation between length ranges and heterogeneity was high (r = 0.88) and significant. These data would suggest that muscles with a similar number of sarcomeres in series can exhibit quite different functional characteristics.

Aging, functional capacity and eccentric exercise training

Aging is a multi-factorial process that ultimately induces a decline in our physiological functioning, causing a decreased health-span, quality of life and independence for older adults. Exercise participation is seen as a way to reduce the impact of aging through maintenance of physiological parameters. Eccentric exercise is a model that can be employed with older adults, due to the muscles ability to combine high muscle force production with a low energy cost. There may however be a risk of muscle damage before the muscle is able to adapt. The first part of this review describes the process of aging and how it reduces aerobic capacity, muscle strength and therefore functional mobility. The second part highlights eccentric exercise and the associated muscle damage, in addition to the repeated bout effect. The final section reviews eccentric exercise interventions that have been completed by older adults with a focus on the changes in functional mobility. In conclusion, eccentric endurance exercise is a potential training modality that can be applied to older adults for improving muscle strength, aerobic capacity and functional ability. However, further research is needed to assess the effects on aerobic capacity and the ideal prescription for eccentric endurance exercise.

Temporal semantics of compositional task models and problem solving methods

Abstract Task models and problem solving methods can be specified informally or formally. In recent years various approaches have formalized the notion of task models or problem solving methods. Most modelling approaches concentrate on the form of a task model or problem solving method rather than on their precise semantics: a formalisation is often only a syntactical formalisation. A more precise definition of the semantics requires explication of the control of a systems behaviour. In this paper temporal semantics is defined for a compositional modelling approach to task models and problem solving methods. The semantics is a description of a compositional systems behaviour; a temporal approach provides a means to describe the dynamics involved. The formalisation of the semantics is based on compositional three-valued temporal models. The compositional structure of information states, transitions and reasoning traces provides a transparent model of the systems behaviour, both conceptually and formally.

Isometric and Concentric Performance of Electrically Stimulated Ankle Plantar Flexor Muscles in Intact Rat

The relationship between muscle force and ankle position during isometric and pre‐loaded slow concentric contractions (angular velocity, 0.52 rad s−1; range of motion, 1.22 rad) and the recovery of isometric force following concentric contractions at different velocities were determined for electrically stimulated plantar flexor muscles in intact rats. Pre‐loaded refers to the isometric contraction which immediately precedes the concentric contraction. Ankle position was controlled by a dynamometer and force was recorded under the sole of the foot. The peak isometric force (19.2 N) was nearly constant at all ankle positions (range of motion, 1.57 rad). The muscle length and distal fibre length of gastrocnemius medialis at ankle positions between 0.79 rad and 2.01 rad were increased by 12.6% and 20.3%, respectively. During slow concentric contractions, the force progressively decreased (23.1 ± 2.1%); the force decreased by only 6.3 ± 0.9% during sustained isometric contractions of similar duration (3400 ms). The recovery of isometric force following concentric contractions with similar stimulation frequencies (80 Hz) was velocity dependent (i.e. more rapid at higher velocities). It is concluded that pre‐loaded slow concentric contractions of the plantar flexor muscles in intact rats do not follow the same relationship as that of isometric force and ankle position. Our results in intact rats show that the force output of electrically stimulated ankle plantar flexor muscles measured under the sole of the foot can be used to study the physiological properties of skeletal muscle working in situ.

Modelling an elevator design task in DESIRE: the VT example

An elevator configuration task, the VT task, is modelled within DESIRE as a design task. DESIRE is a framework within which complex reasoning tasks are modelled as compositional architectures. Compositional architectures are based on a task decomposition, acquired during task analysis. An existing generic task model of design, based on a logical analysis and synthesis of task models devised for diverse applications, has been refined for the elevator configuration task. The resulting task model includes a description of the ontology of the elevator domain and a description of the task model.

Projection and Unification for Conceptual Graphs

In this paper we will investigate subsumption and unification for structured descripitons by considering conceptual graphs with their projection and (maximal) join. The importance of projection for conceptual graphs is well-known as it essentially defines a partial order (subsumption hierarchy) on the graphs, that allows one to speed up search considerably. We investigate the complexity of projection by introducing a weaker notion of structural similarity, polyprojection. We prove that a polyprojection implies a projection for so-called non-repeating conceptual graphs. Furthermore, we show that a polyprojection can be determined by a polynomial algorithm. Indeed, the algorithm presented generalizes well-known algorithms for subtree isomorphism, and subsumption between feature term graphs.

Effect of resistance training on muscle fatigue and recovery in intact rats

PURPOSE To examine the effect of resistance training on muscle fatigue from intermittent contractions and subsequent recovery in intact rats. METHODS By using electrical stimulation, plantar flexor muscles were trained with eccentric and concentric contractions (5 x 10 repetitions, 5 d x wk(-1) for 6 wk) during ankle rotations. By using nerve stimulation, concentric contractions (40) imposed on isometric contractions (stimulation time, 1.9 s; rest period, 13.6 s; intermittent contractions) induced fatigue. During recovery, equivalent contractions were used every 5 min for 30 min. RESULTS Training increased isometric forces (19% and 23% at ankle positions of 1.57 and 0.70 rad), but muscle weights were not changed. After training, smaller declines in isometric (control, 68.9+/-1.4%; trained, 58.8+/-2.9%) and average concentric force (control, 71.6+/-0.7%; trained, 65.5+/-2.8%) occurred from fatigue. Recovery for 5 min returned isometric and average concentric force to 61.7+/-2.2% and 65.1+/-2.5% of initial values for controls and 76.9+/-2.2% and 77.1+/-2.2% after training. After recovery for 30 min, these forces were 87.6+/-0.7% and 89.2+/-1.1% of initial values for controls and recovered almost completely (94.2+/-1.3% and 94.6+/-1.6%) in trained muscles. During fatigue, the decline in force during successive concentric contractions was larger after training (from 19.7+/-1.1% to 50.1+/-2.0%; controls, from 19.9+/-2.0% to 41.7+/-1.4%). Recovery of this decline in force was training-independent and complete within 5 min. CONCLUSIONS Rat plantar flexor muscles adapt to 6 wk of 5 d x wk(-1) resistance training with: 1) increased isometric force, 2) smaller losses in isometric and average concentric force during fatigue, 3) larger force decline during concentric contractions during fatigue, and 4) improved recovery following fatigue. Different mechanisms might account for the recovery of the average concentric force and the decline in force during concentric contractions.

Neuromuscular and cardiovascular responses of Royal Marine recruits to load carriage in the field.

Cardiovascular and neuromuscular responses of 12 male Royal Marine recruits (age 22 ± 3 years, body mass 80.7 ± 6.8 kg, VO(2)max 52.3 ± 2.7 ml kg(-1) min(-1)) were measured during 19.3 km of load carriage walking at 4.2 km h(-1) and carrying 31.0 kg. Heart rate during load carriage was 145 ± 10 beats·min(-1) (64 ± 5 %HRR) and showed a negative relationship with body mass (r = -0.72, P = 0.009) but no relationship with VO(2)max (ml kg(-1) min(-1); r = -0.40, P = 0.198). Load carriage caused a decrease in vertical jump height (8 ± 9%) and power (5 ± 5%) (P < 0.001). Change in vertical jump power showed a positive relationship with body mass (r(2) = 0.40, P = 0.029) but no relationship to VO(2)max (ml kg(-1) min(-1); r(2) = 0.13, P = 0.257). In conclusion, load carriage caused a reduction in vertical jump performance (i.e. decreased neuromuscular function). Lighter individuals were disadvantaged when carrying absolute loads, as they experienced higher cardiovascular strain and greater decreases in neuromuscular function.

Comparison of Physiological and Metabolic Responses to Playing Nintendo Wii Sports and Brisk Treadmill Walking

Comparison of Physiological and Metabolic Responses to Playing Nintendo Wii Sports and Brisk Treadmill Walking Regular moderate-intensity exercise (e.g. brisk walking) provides health benefits. In the present study, we compared the physiological and metabolic responses of playing the Nintendo Wii Sports tennis, baseball and boxing with self-paced brisk treadmill walking. Ten young-adults (21±1 years; 73.9±12.0 kg; 1.76±0.06 m) played each sport for 10 min with a 5 min rest interval or, in a separate session, walked briskly (6.1±0.6 km·h-1) with an equivalent time order wearing the Cosmed K4b2 metabolic system. In a bout of 10 min, the average values during Nintendo Wii boxing for physiological (i.e. minute ventilation, oxygen uptake and heart rate) and metabolic (i.e. energy expenditure, fat oxidation, carbohydrate oxidation and respiratory exchange ratio) responses were equal to brisk treadmill walking but lower for Nintendo Wii tennis and baseball (P<0.05). It was concluded that the physiological and metabolic responses of Nintendo Wii boxing would allow this game activity to be a viable part of a programme of structured exercise in young-adults to gain health benefits.

Mechanical and structural characteristics of single muscle fibres and fibre groups from raw and cooked pork longissimus muscle

The aim of this study was to analyse the mechanisms that determine why small groups of muscle fibres may have different mechanical properties than single muscle fibres. The method used combined light microscopy and tensile testing on single fibres and small groups of fibres from raw and cooked (80 °C) meat, from both conditioned and unconditioned porcine longissimus muscle. The results showed that small groups of fibres had different breaking properties than constituent single fibres in raw muscle, but that these differences diminished on cooking. Raw groups of fibres showed a more uniform lengthening along their entire length and a higher extension to rupture than single fibres. Conditioning increased maximum strains in both single fibres and small fibre groups. In unconditioned cooked meat, single fibres and fibre groups showed comparable breaking stresses and extensions. Conditioning resulted in a lower strength in fibre groups than in single fibres. These results show that (endomysial) connective tissue linkages between adjacent muscle fibres in a small group significantly alter the breaking behaviour of single fibres. The effects of these connective tissue linkages are not reduced by conditioning alone, but are largely diminished by cooking to 80 °C.