This meticulous and careful research was carried out by Christina Karatzaferi as part of her PhD working under the supervision of Professor Anthony J Sargeant. The results confirm and validate previous published work and speculation by Tony Sargeant in 1987 (published in the Journal of Applied Physiology) showing the time course of the recovery of high energy phosphate levels in human muscle following maximum sprint exercise. In the 1987 paper it was impossible at that time to measure the PCr and ATP levels in single fibres and the conclusions were based on recovery of muscle power. The present paper was able to link this to a metabolic cause, that is the dependence upon the replenishment of the high energy phosphates in the muscle.
The recovery of high-energy phosphate levels in single human skeletal muscle fibres following short-term maximal (all-out) exercise was investigated. Three male volunteers exercised maximally for 25 s on an isokinetic cycling ergometer. Muscle biopsy samples from the vastus lateralis were collected at rest, immediately post-exercise and at 1.5 min of recovery. The subjects also performed a second exercise bout 1.5 min after the first, on a separate occasion. Single muscle fibres were dissected, characterized and assigned to one of four groups according to their myosin heavy chain (MyHC) isoform content; namely, type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC). Fibres were analysed for adenosine 5′-triphosphate (ATP), inosine-5′-monophosphate (IMP), phosphocreatine (PCr) and creatine (Cr) levels. Type I fibres had a lower Cr content than type II fibres (P<0.01). Within type II fibres resting [PCr] increased with increasing MyHC IIX isoform content (r=0.59, P<0.01). Post-exercise [PCr] was very low in all fibre groups (P<0.01 versus rest) while great reductions in ATP were also observed (P<0.01 versus rest), especially in the type II fibre groups. [PCr] at 1.5 min of recovery was still lower compared to rest for all fibre groups (P<0.01) especially in the IIAx and IIXa fibres
In order to calculate mechanical efficiency during human exercise the total power generated needs to be known. That is the external power delivered to some ergometer plus the internal power required to move the limb. This research carried out in Copenhagen in collaboration with Jens Bangsbo and Per Aagaard addresses this problem. The research publication formed part of the PhD thesis of Richard Ferguson which work was directed by Derek Ball and Professor Anthony J Sargeant.
A novel approach has been developed for the quantification of total mechanical power output produced by an isolated, well-defined muscle group during dynamic exercise in humans at different contraction frequencies. The calculation of total power output comprises the external power delivered to the ergometer (i.e., the external power output setting of the ergometer) and the “internal” power generated to overcome inertial and gravitational forces related to movement of the lower limb. Total power output was determined at contraction frequencies of 60 and 100 rpm. At 60 rpm, the internal power was 18+/- 1 W (range: 16-19 W) at external power outputs that ranged between 0 and 50 W. This was less (P<0.05) than the internal power of 33+/-2 W (27-38 W) at 100 rpm at 0-50 W. Moreover, at 100 rpm, internal power was lower (P<0.05) at the higher external power outputs. Pulmonary oxygen uptake was observed to be greater (P<0.05) at 100 than at 60 rpm at comparable total power outputs, suggesting that mechanical efficiency is lower at 100 rpm. Thus a method was developed that allowed accurate determination of the total power output during exercise generated by an isolated muscle group at different contraction frequencies
This research publication in the medical journal ‘Spinal Cord’ formed part of a research programme carried out by HL Gerrits under the direction and supervision of Professor Maria Hopman of Radboud University of Nijmegen, Professor Anthony J Sargeant and Arnold de Haan of the Vrije University of Amsterdam. The publication formed a chapter in the PhD thesis of Ms Gerrits.
OBJECTIVES: To assess if contractile speed and fatigability of paralysed quadriceps muscles in individuals with spinal cord injury (SCI) can be altered by functional electrical stimulation leg cycle ergometry (FES-LCE) training.
SETTINGS: The Sint Maartenskliniek rehabilitation centre and the University of Nijmegen, Nijmegen, the Netherlands.
METHODS: Contractile properties of the quadriceps muscle were studied in seven people with motor-complete SCI who participated in a FES-LCE training program. Subjects trained for 30 min, three times per week for 6 weeks. Contractile speed and fatigue characteristics of electrically stimulated isometric contractions were compared before and after 6 weeks of FES-LCE.
RESULTS: Fatigue resistance improved following FES-LCE training as indicated by the higher forces maintained in response to repetitive electrical stimulation. In contrast with an improved fatigue resistance, the maximal rate of force rise was unaffected, the speed of relaxation increased and the fusion of a 10 Hz force signal decreased. Furthermore, the force-frequency relationship shifted to the right at low stimulation frequencies, indicated by a decline in the ratio of 1 and 100 Hz force responses as well as the ratio of 10 and 100 Hz force responses.
CONCLUSION: FES-LCE training can change the physiological properties of the quadriceps muscle in people with SCI. Even after a short period of training, the stimulated muscles become more resistant to fatigue. Furthermore, the increased speed of relaxation and associated decreased fusion and altered force-frequency relationship following training may be related to adaptations in the calcium handling processes, which reflect an early response of long-term disused muscles.
The purpose of the present study was to investigate the effect of temperature on the rates of isometric force development and relaxation in electrically activated fresh and fatigued human adductor pollicis muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, muscle temperatures were approximately 37, 31, 25 and 22 C. Maximal isometric force was reduced by 16.8 +/- 1.5 % at 22 C. The stimulation frequency-force and -rate of force development relationships were shifted to the left at lower temperatures. Q10 values for the maximal rates of force development and relaxation, and the times for 100 to 50 % and 50 to 25 % force relaxation, were about 2.0 between 37 and 25 C and about 3.8 between 25 and 22 C. However, the time for 50 to 25 % force relaxation had a relatively high Q10 value between 25 and 22 C (6.9) and this parameter also appeared to be more sensitive to fatigue compared to the other indices of relaxation. Nevertheless, the effect of fatigue on all parameters decreased with cooling over the entire (37-22 C) temperature range
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
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.
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.
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.
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.
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