Changes in mechanical leverage of muscles occur as a result of contraction making modelling uncertain

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Part of an important series of research publications by the talented Costis Maganaris (now a deservedly full professor in his own right) as part of his PhD which was supervised by Professors Anthony Sargeant and Vasilios Baltzopoulos

Changes in the tibialis anterior tendon moment arm from rest to maximum isometric dorsiflexion: in vivo observations in man

Costis N Maganaris, Vassilios Baltzopoulos, Anthony J Sargeant.

Clinical Biomechanics
Clin Biomech (Bristol, Avon). 1999 Nov;14(9):661-6
Abstract
OBJECTIVE: In the present study, we examined the hypothesis that the tibialis anterior tendon moment arm increases during maximum isometric dorsiflexion as compared with rest.
BACKGROUND: In musculoskeletal modelling applications, moment arms from passive muscles at rest are assumed representative of those measured during isometric muscle contraction. The validity of this assumption is questionable in musculotendon actuators enclosed by retinacular systems as in tibialis anterior.
DESIGN AND METHODS: Sagittal-plane magnetic resonance images of the right ankle were taken in six subjects at rest and during maximum isometric dorsiflexion at six ankle angles between dorsiflexion and plantarflexion having the body placed in the supine position and the knee flexed at 90 degrees. Instant centres of rotation in the tibio-talar joint, tibialis anterior tendon action lines and moment arms were identified in the sagittal plane at ankle angles of -15 degrees, 0 degrees,+15 degrees and +30 degrees at rest and during maximum isometric dorsiflexion.
RESULTS: At any given ankle angle, the tibialis anterior tendon moment arm during maximum isometric dorsiflexion increased by 0.9-1.5 cm (P<0.01) compared with rest. This was attributed to a displacement of both tibialis anterior tendon action line by 0.8-1.2 cm (P<0.01) and all instant centres of rotation by 0.3-0.4 cm (P<0. 01) distally in relation to their corresponding resting positions.
CONCLUSIONS AND IMPLICATIONS: The assumption that the tibialis anterior tendon moment arm does not change from rest to maximum isometric dorsiflexion is invalid. Erroneous tendon forces, muscle stresses and joint moments by as much as 30% would be calculated using resting tibialis anterior tendon moment arms in the moment equilibrium equation around the ankle joint during maximum isometric dorsiflexion. RELEVANCE: A substantial increase in the tibialis anterior tendon moment arm occurs from rest to maximum isometric dorsiflexion. This needs to be taken into consideration when using planimetric musculoskeletal modelling for analysing maximal static ankle dorsiflexion loads.
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Spinal cord injury in humans – Functional Electrical Stimulation

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This research formed part of the PhD thesis of HL (Karin) Gerrits which was directed by Professor Anthony J Sargeant together with Maria Hopman, David Jones and others.

The results may be useful to optimize stimulation characteristics for functional electrical stimulation and to monitor training effects induced by electrical stimulation during rehabilitation of paralyzed muscles.

Contractile properties of the quadriceps muscle in individuals with spinal cord injury

Gerrits HL, Arnold de Haan, Maria T Hopman, Luc H van Der Woude, David A Jones, Anthony J Sargeant

Muscle Nerve. 1999 Sep;22(9):1249-56

Abstract
Selected contractile properties and fatigability of the quadriceps muscle were studied in seven spinal cord-injured (SCI) and 13 able-bodied control (control) individuals. The SCI muscles demonstrated faster rates of contraction and relaxation than did control muscles and extremely large force oscillation amplitudes in the 10-Hz signal (65 +/- 22% in SCI versus 23 +/- 8% in controls). In addition, force loss and slowing of relaxation following repeated fatiguing contractions were greater in SCI compared with controls. The faster contractile properties and greater fatigability of the SCI muscles are in agreement with a characteristic predominance of fast glycolytic muscle fibers. Unexpectedly, the SCI muscles exhibited a force-frequency relationship shifted to the left, most likely as the result of relatively large twitch amplitudes. The results indicate that the contractile properties of large human locomotory muscles can be characterized using the approach described and that the transformation to faster properties consequent upon changes in contractile protein expression following SCI can be assessed. These measurements may be useful to optimize stimulation characteristics for functional electrical stimulation and to monitor training effects induced by electrical stimulation during rehabilitation of paralyzed muscles.

Force-velocity relationship of human muscle

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The research idea for this study came from Professor Anthony J Sargeant of Amsterdam and Professor David Jones (Birmingham University). It was the culmination of many years of Tony Sargeant encouraging members of his research group in Amsterdam to adapt a technique for studying rat muscle force velocity to small human hand muscles. The data was finally collected by Jo de Ruiter a post-doc in the Amsterdam research group.

The measurement of force/velocity relationships of fresh and fatigued human adductor pollicis muscle.

CJ De Ruiter, David A Jones, Anthony J Sargeant, Arnold de Haan.

European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1999 Sep;80(4):386-93
The purpose of the study was to obtain force/velocity relationships for electrically stimulated (80 Hz) human adductor pollicis muscle (n = 6) and to quantify the effects of fatigue. There are two major problems of studying human muscle in situ; the first is the contribution of the series elastic component, and the second is a loss of force consequent upon the extent of loaded shortening. These problems were tackled in two ways. Records obtained from isokinetic releases from maximal isometric tetani showed a late linear phase of force decline, and this was extrapolated back to the time of release to obtain measures of instantaneous force. This method gave usable data up to velocities of shortening equivalent to approximately one-third of maximal velocity. An alternative procedure (short activation, SA) allowed the muscle to begin shortening when isometric force reached a value that could be sustained during shortening (essentially an isotonic protocol). At low velocities both protocols gave very similar data (r2 = 0.96), but for high velocities only the SA procedure could be used. Results obtained using the SA protocol in fresh muscle were compared to those for muscle that had been fatigued by 25 s of ischaemic isometric contractions, induced by electrical stimulation at the ulnar nerve. Fatigue resulted in a decrease of isometric force [to 69 (3)%], an increase in half-relaxation time [to 431 (10)%], and decreases in maximal shortening velocity [to 77 (8)%] and power [to 42 (5)%].
These are the first data for human skeletal muscle to show convincingly that during acute fatigue, power is reduced as a consequence of both the loss of force and slowing of the contractile speed

RNA content in mammalian muscle fibres

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This important research was part of the PhD work carried out by Petra Habets in the research group headed by Professor Anthony J Sargeant. It was a collaboration and jointly supervised by Anton Moorman of the Academic Medical Centre, of the University of Amsterdam. Sadly one of the inspirations for this research and close friend Jose Sant’Ana Pereira died, much too young, a few years after this work was published while working in the University of Madison, Wisconsin.

RNA content differs in slow and fast muscle fibers: implications for interpretation of changes in muscle gene expression

Petra E.M.H. Habets, Diego Franco, Jan M. Ruijter, Anthony J. Sargeant, José A.A. Sant’Ana Pereira, Anton F.M. Moorman.

Journal of Histochemistry and Cytochemistry
J Histochem Cytochem. 1999 Aug;47(8):995-100
Quantification of a specific muscle mRNA per total RNA (e.g., by Northern blot analysis) plays a crucial role in assessment of developmental, experimental, or pathological changes in gene expression. However, total RNA content per gram of a particular fiber type may differ as well.
We have tested this possibility in the distinct fiber types of adult rat skeletal muscle.
Sections of single fibers were hybridized against 28S rRNA as a marker for RNA content.
Quantification of the hybridization showed that the 28S rRNA content decreases in the order I>IIA>IIX>IIB, where Type I fibers show a five- to sixfold higher expression level compared to Type IIB fibers. Results were verified with an independent biochemical determination of total RNA content performed on pools of histochemically defined freeze-dried single fibers. In addition, the proportion of myosin heavy chain (MHC) mRNA per microgram of total RNA was similar in slow and fast fibers, as demonstrated by Northern blot analysis.
Consequently, Type I fibers contain five- to sixfold more MHC mRNA per microgram of tissue than IIB fibers. These differences are not reflected in the total fiber protein content.
This study implies that proper assessment of mRNA levels in skeletal muscle requires evaluation of total RNA levels according to fiber type composition

Measurement of high-energy phosphates in tiny fragments of human muscle fibres

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This research method was  developed in the group headed by Professor Anthony J Sargeant in Amsterdam. Arnold de Haan had developed the basis of the technique in the 1980s as part of his own PhD work. This was subsequently refined to enable very small fragments of human muscle fibre obtained by needle biopsy to be analysed. The present research paper describes that refined techniques and its sensitivity. The work formed part of the PhD thesis the outstanding Greek PhD student, Christina Karatzaferi, who was supervised by Tony Sargeant and Arnold de Haan.

Improved high-performance liquid chromatographic assay for the determination of “high-energy” phosphates in mammalian skeletal muscle. Application to a single-fibre study in man

Christina Karatzaferi, Arnold de Haan, Carla Offringa, Anthony J Sargeant.

Journal of Chromotography

J Chromatogr B Biomed Sci Appl. 1999 Jul 9;730(2):183-91
Abstract
A sensitive and reproducible method for the determination of adenine nucleotides (ATP, IMP) and creatine compounds [creatine (Cr), phosphocreatine (PCr)] in freeze-dried single human muscle fibre fragments is presented. The method uses isocratic reversed-phase high-performance liquid chromatography of methanol extracts. Average retention times (min) of ATP, IMP and PCr, Cr from standard solutions were 10.6+/-0.42, 2.11+/-0.06 (n=6) and 10.5+/-0.31 and 1.19+/-0.02 (n=9), respectively. Detection limits in extracts from muscle fibre fragments were 2.0, 1.0, 3.0 and 2.0 mmol/kg dm, respectively. The assay was found successful for analysis of fibre-fragments weighing > or = 1 microg.

Performing Sprint Exercise in the heat

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This research was largely carried out by Derek Ball. It looks at the effect of heat stress on human sprinting performance and has implications for sporting activities. Derek Ball was originally a post-doctoral fellow (later Senior Lecturer) in the research group and later Institute headed by Professor Anthony J Sargeant.

Human power output during repeated sprint cycle exercise: the influence of thermal stress

Derek Ball, Burrows C , Anthony J Sargeant.

European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1999 Mar;79(4):360-6
    Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise.
    On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4 min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7 (1.5) degrees C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1 (0.5) degrees C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration.
    Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172) W vs 656 (58) W; P < 0.01] and sprint II [907 (150) vs 646 (37) W; P < 0.05]. Mean power output was higher in the heat compared to the normal environment in both sprint I [634 (91) W vs 510 (59) W; P < 0.05] and sprint II [589 (70) W vs 482 (47) W; P < 0.05]. There was a faster rate of fatigue (P < 0.05) when exercise was performed in the heat compared to the normal environment. Arterialised-venous blood samples were taken for the determination of acid-base status and blood lactate and blood glucose before exercise, 2 min after sprint I, and at several time points after sprint II. Before exercise there was no difference in resting acid-base status or blood metabolites between environmental conditions. There was a decrease in blood pH, plasma bicarbonate and base excess after sprint I and after sprint II. The degree of post-exercise acidosis was similar when exercise was performed in either of the environmental conditions. The metabolic response to exercise was similar between environmental conditions; the concentration of blood lactate increased (P < 0.01) after sprint I and sprint II but there were no differences in lactate concentration when comparing the exercise bouts performed in a normal and a hot environment.
    These data demonstrate that when brief intense exercise is performed in the heat, peak power output increases by about 25% and mean power output increases by 15%; this was due to achieving a higher pedal cadence in the heat

Post-Polio Syndrome

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The data collection and analysis of this research study was largely the work of Frans Nollet and Anita Beelen. Other senior authors provided input at various stages of planning and writing. Professor Anthony J Sargeant was the supervisor for the PhD thesis of which this work formed a part.

Disability and functional assessment in former polio patients with and without postpolio syndrome

Frans Nollet, Anita Beelen, Prins MH, Marianne de Visser, Anthony J Sargeant, Lankhorst GJ, de Jong BA 

Archives of Physical Medicine and Rehabilitation

Arch Phys Med Rehabil. 1999 Feb;80(2):136-143
Abstract
OBJECTIVES: To compare perceived health problems and disability in former polio subjects with postpolio syndrome (PPS) and those without postpolio syndrome (non-PPS), and to evaluate perceived health problems, disability, physical performance, and muscle strength.
DESIGN: Cross-sectional survey; partially blinded data collection.
SUBJECTS: One hundred three former polio subjects, aged 32 to 60yrs. This volunteer sample came from referrals and patient contacts. Criterion for PPS: new muscle weakness among symptoms.
MAIN OUTCOME MEASURES: Nottingham Health Profile (NHP), adapted D-code of the International Classification of Impairments, Disabilities and Handicaps, performance test, and muscle strength assessment.
RESULTS: PPS subjects (n = 76) showed higher scores (p < .001) than non-PPS subjects (n = 27) within the NHP categories of physical mobility, energy, and pain. On a 16-item Polio Problems List, 78% of PPS subjects selected fatigue as their major problem, followed by walking outdoors (46%) and climbing stairs (41%). The disabilities of PPS subjects were mainly seen in physical and social functioning. No differences in manually tested strength were found between patient groups. PPS subjects needed significantly more time for the performance test than non-PPS subjects and their perceived exertion was higher. Perceived health problems (NHP-PhysMobility) correlated significantly with physical disability (r = .66), performance-time (r = .54), and muscle strength (r = .38). With linear regression analysis, 54% of the NHP-PhysMobility score could be explained by the performance test (time and exertion), presence of PPS, and muscle strength, whereas strength itself explained only 14% of the NHP-PhysMobility score.
CONCLUSIONS: PPS subjects are more prone to fatigue and have more physical mobility problems than non-PPS subjects. In former polio patients, measurements of perceived health problems and performance tests are the most appropriate instruments for functional evaluation