Muscle is less strong and less efficient in young when compared with older animals

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This research carried out in the Department of Anthony Sargeant in Amsterdam demonstrated how during rapid growth the muscle of young animals is weaker and less efficient compared with older animals.
Acta Physiologica Scandanavica
Acta Physiol Scand. 1993 Apr;147(4):347-55

We investigated the effect of age on (the reduction of) work output, efficiency and muscle fibre type composition. Rat medial gastrocnemius muscles of three age-groups performed a series of 15 repeated contractions within 6 s (blood flow was arrested). Stimulation and shortening velocities were chosen as optimal for each group, while all muscles shortened over the same relative fibre lengths.

The fibre type composition showed a higher proportion of the oxidative type IIBd fibres in the middle-aged group [5 months old; 39.8 +/- 6.8 vs. 23.6 +/- 4.2% of the fibre area in the young rats (1.3 months old)] in contrast to the type IIBm fibres (52.9 vs. 67.9%, respectively), while the old group (22 months old) was not different from the middle-aged group. Work output in the last contraction (relative to the first contraction) was not different between the age-groups (53.1 +/- 18.1; 48.0 +/- 6.5 and 61.1 +/- 6.2%, respectively). High-energy phosphate utilization was not different between the groups (150.6 +/- 11.2; 154.6 +/- 15.6 and 157.2 +/- 7.0 mumol g-1 dry wt, respectively). However, the efficiency was approximately 30% lower in the muscles of the youngest group, which corresponds with a lower specific power and specific tension. Since the change in fibre type composition is unlikely to be the cause of the low efficiency in the young animals, the causes remain unclear, but may be related to the rapid growth of the young rats in our study.

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Fatigue during cycling is related to pedalling rate

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Research carried out by Anita Beelen under the direction of Anthony Sargeant extended his interest in short-term muscle power output (sometimes referred to as anaerobic power). In cycling it can be seen that the degree of fatigue from prior exercise is greater when measured at higher pedalling rates. This is consistent with fatigue inducing prior exercise reducing the power generation of the faster of the most fatigue sensitive muscle fibres in the mixed human leg muscles.
European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1993;66(2):102-107

The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev.min-1, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake (VO2max), whether performed at a pedalling frequency of 60 or 120 rev.min-1, reduced maximal STPO generated at 120 rev.min-1 to a much greater extent than maximal STPO at 60 rev.min-1. After 6-min submaximal exercise at 60 rev.min-1 mean reductions in maximal STPO measured at 120 and 60 rev.min-1 were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev.min-1, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev.min-1. Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev.min-1. Nevertheless, maximal STPO generated at 120 rev.min-1 was reduced after exercise at 120 rev.min-1 [20 (SD 13)%, P < 0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of growth and ageing on muscle properties

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Margriet Lodder completed this research as part of her PhD which was supervised by Anthony Sargeant and Arnold de Haan. The research examined age related changes in muscle properties using a rat model.
Journal of Muscle Research and Cell Motility
J Muscle Res Cell Motil. 1993 Feb;14(1):47-53

Morphological and functional changes as well as changes in fibre-type composition were investigated in the left extensor digitorum longus (EDL) muscles of male Wistar rats of approximately 40, 60, 120 and 700 days old. A number of morphological changes occurred in the EDL muscle during growth. While from 40 to 120 days muscle mass and cross-sectional area (CSA) increased by 247 and 192%, changes in muscle and fibre lengths were much smaller (44 and 17%, respectively).

Besides morphological changes tetanic force was also found to increase (approximately 307%) up to 120 days. Because this increase in force was greater than the increase in CSA, specific force increased by approximately 29% between 40 and 60 days. Thereafter, specific force stayed rather constant. From 40 until 60 days changes were also found in the force-frequency and force-velocity curve, which indicate a slowing of the muscles (until 60 days). Changes in fibre-type composition of the EDL muscle were found to occur later during growth between 60 and 120 days. In this period an increase in the relative total area of Type IIBd fibres and a decrease in the relative total area of Type IIBm fibres (corresponding to the Type 2X and IIB fibres, respectively), were found; this was apparently due to a conversion of many Type IIBm into Type IIBd fibres and not to a difference in cross-sectional growth between these fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Leg muscle force generated by electrical stimulation following spinal cord injury in humans

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The data for this research paper was collected by HL Gerrits as part of her PhD programme into muscle tendon function following spinal cord injury in humans. It was completed under the supervision of Anthony Sargeant.

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

Human Musculo-tendon properties: Methodological considerations

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Detailed measurements using ultra-sonography underpin this important contribution to research on musculo tendon function in the intact human.
Clinical Biomechanics
Clin Biomech (Bristol, Avon). 1999 Nov;14(9):661-6

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

The effect of muscle temperature on force measured directly in human muscle

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Sometimes strange things happen in scientific research. The very senior authors Anthony Sargeant and David Jones were responsible for initiating, carrying out experiments, and plotting much of the data that formed the basis of this and another paper to Journal of Physiology. Nevertheless having spent some time getting the research started on visits to Amsterdam they were both surprised to see this paper submited along with another to Journal of Physiology (on which there names do not even appear as authors). There is nothing wrong with either paper but courtesy and proper recognition by junior colleagues of the conceptual origins and contribution would have been more correct behaviour.
Experimental Physiology
Exp Physiol. 1999 Nov;84(6):1137-50

Abstract 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

How the ‘reserve’ of power generating capability may be important in choosing pedalling rate in cycling

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This research built on the previous work of Anthony Sargeant looking at the maximum short term power generated by human muscle. In this study what became apparent is that the reserve of power is dependent upon the power velocity relationship of the leg muscles.
The data was collected in Amsterdam by a visiting Polish colleague from Krakow, Jerzy Zoladz working with Tony Sargeant’s PhD student at the time (Dr Arno Rademaker).
Experimental Physiology
Exp Physiol. 2000 Jan;85(1):117-24

Abstract The effect of different pedalling rates (40, 60, 80, 100 and 120 rev min-1) on power generating capability, oxygen uptake (O2) and blood lactate concentration [La]b during incremental tests was studied in seven subjects. No significant differences in O2,max were found (mean +/- S.D, 5.31 +/- 0.13 l min-1). The final external power output delivered to the ergometer during incremental tests (PI,max) was not significantly different when cycling at 60, 80 or 100 rev min-1 (366 +/- 5 W). A significant decrease in PI,max of 60 W was observed at 40 and 120 rev min-1 compared with 60 and 100 rev min-1, respectively (P < 0.01). At 120 rev min-1 there was also a pronounced upward shift of the O2-power output (O2-P) relationship. At 50 W O2 between 80 and 100 rev min-1 amounted to +0.43 l min-1 but to +0.87 l min-1 between 100 and 120 rev min-1. The power output corresponding to 2 and 4 mmol l-1 blood lactate concentration (P[La]2 and P[La]4 ) was also significantly lower (> 50 W) at 120 rev min-1 (P < 0.01) while pedalling at 40, 60, 80 and 100 rev min-1 showed no significant difference. The maximal peak power output (PM, max) during 10 s sprints increased with pedalling rate up to 100 rev min-1. Our study indicates that with increasing pedalling rate the reserves in power generating capability increase, as illustrated by the PI,max/PM,max ratio (54.8, 44.8, 38.1, 34.6, 29.2%), the P[La]4/PM,max ratio (50.4, 38.9, 31.0, 27.7, 22.9%) and the P[La]2/PM,max ratio (42.8, 33.5, 25.6, 23.1, 15.6%) increases. Taking into consideration the O2,max, the PI,max and the reserve in power generating capability we concluded that choosing a high pedalling rate when performing high intensity cycling exercise may be beneficial since it provides greater reserve in power generating capability and this may be advantageous to the muscle in terms of resisting fatigue. However, beyond 100 rev min-1 there is a decrease in external power that can be delivered for an given O2 with an associated earlier onset of metabolic acidosis and clearly this will be disadvantageous for sustained high intensity exercise.