Intrinsic strength of human muscle

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In this research carried out in the Research Institute directed by Anthony Sargeant the very talented and productive Costis Maganaris used ultrasonography and MRI to determine intrinsic strength of human muscle in vivo.
Journal of Applied Physiology
J Appl Physiol. 2001 Mar;90(3):865-72

Abstract

In this study, we estimated the specific tensions of soleus (Sol) and tibialis anterior (TA) muscles in six men. Joint moments were measured during maximum voluntary contraction (MVC) and during electrical stimulation. Moment arm lengths and muscle volumes were measured using magnetic resonance imaging, and pennation angles and fascicular lengths were measured using ultrasonography.

Tendon and muscle forces were modeled. Two approaches were followed to estimate specific tension. First, muscle moments during electrical stimulation and moment arm lengths, fascicular lengths, and pennation angles during MVC were used (data set A). Then, MVC moments, moment arm lengths at rest, and cadaveric fascicular lengths and pennation angles were used (data set B). The use of data set B yielded the unrealistic specific tension estimates of 104 kN/m(2) in Sol and 658 kN/m(2) in TA. The use of data set A, however, yielded values of 150 and 155 kN/m(2) in Sol and TA, respectively, which agree with in vitro results from fiber type I-predominant muscles. In fact, both Sol and TA are such muscles. Our study demonstrates the feasibility of accurate in vivo estimates of human muscle intrinsic strength

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A peculiar form of human locomotion – Speed-skating

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Anthony Sargeant moved to the Netherlands in 1985 as Professor and Head of Department with a joint appointment in the University of Amsterdam and the Vrije University of Amsterdam. The passion for Speed skating was ubiquitous and he contributed some physiological insights into this research review which sought to describe the peculiar nature of this form of locomotion. Peculiar because paradoxically it crucially depends upon muscles not shortening doing work and generating muscle power but rather remaining in a fixed isometric contraction. It is the ability to sustain a low aerodynamic profile during the long glide element of the cycle which is the key to success. As the skater fatigues and can no longer maintain a low profile the body position rises and this leads to greater air-resistance and hence a slower speed in the long glide phase.
Journal of Sports Science
J Sports Sci. 1987 Winter;5(3):249-59

Speed skating exercise can be better understood by taking account of physiological and biomechanical considerations. Comparison with other sports shows the unique and peculiar way of skating propulsion. The relatively long lasting isometric muscle contractions during the gliding phase, alternated with high power output push-offs, place unusual demands on the (local) energy delivering systems.

The short and explosive push-off needs a specific pattern of motor unit recruitment. Some mixture of slow twitch (to sustain skating posture) and fast twitch fibres (to effect push off) in the hip and knee extensors seems necessary for optimal skating performance.

Fatigue in 10 second sprints and human muscle fibre type

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This research was carried out by the talented Christina Karatzaferi as part of her PhD under the direction of Tony Sargeant. Utilizing techniques developed in his laboratory fragments of human muscle fibres were micro-dissected from samples obtained using the needle biopsy technique immediately after a 10 second sprint. Separated fragments were then classified according to fibre type. The level of high energy phosphate was measured in each fibre type and compared to the levels before exercise. This study is part of a long series concerned with anaerobic power and fatigue in human muscle starting with the paper published in 1981 (Sargeant, Hoinville and Young 1981 – note: although not written up until 1981 the work for this paper was actually conducted in the mid 1970s when Tony was working for the Medical Research Council).
Experimental Physiology
Exp Physiol. 2001 May;86(3):411-5

Abstract:

Changes in high-energy phosphate levels in single human skeletal muscle fibres after 10 s of maximal (all-out) dynamic exercise were investigated. Muscle biopsies from vastus lateralis of two volunteers were collected at rest and immediately post exercise. Single muscle fibres were dissected from dry muscle and were assigned into one of four groups according to their myosin heavy chain (MyHC) isoform content: that is type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC).

Fragments of characterised fibres were analysed by HPLC for ATP, inosine-monophosphate (IMP), phosphocreatine (PCr) and creatine levels. After 10 s of exercise, PCr content ([PCr]) declined by approximately 46, 53, 62 and 59 % in type I, IIA, IIAx and IIXa fibres, respectively (P < 0.01 from rest). [ATP] declined only in type II fibres, especially in IIAx and IIXa fibres in which [IMP] reached mean values of 16 +/- 1 and 18 +/- 4 mmol (kg dry mass)(-1), respectively. While [PCr] was reduced in all fibre types during the brief maximal dynamic exercise, it was apparent that type II fibres expressing the IIX myosin heavy chain isoform were under a greatest metabolic stress as indicated by the reductions in [ATP].

Human Fatigue and Muscle Power

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This research was part of a series of investigations into human muscle power generated in short term sprints. The data was collected in London at the beginning of the 1980s with a talented PhD student Patricia Dolan. It is perhaps interesting that the necessarily indirect conclusions of this research with respect to the significance of depletion of High Energy Phosphates as a cause of fatigue in human muscle were later confirmed and elaborated upon in series of elegant experiments by Professor Sargeant’s research groups in Amsterdam and Manchester. In the later experiments conducted 20 years later new techniques developed in those laboratories allowed direct measurements of Phosphocreatine and Adenosine Triphosphate to be made made from isolated and characterised fragments of single muscle fibres obtained by needle biopsy of human quadriceps muscle. An example of one of this series of later papers is the previous post on this site (Karatzaferi et al, 2001)
Journal of Applied Physiology
J Appl Physiol. 1987 Oct;63(4):1475-80

The effect of prior exercise (PE) on subsequent maximal short-term power output (STPO) was examined during cycling exercise on an isokinetic ergometer. In the first series of experiments the duration of PE at a power output equivalent to 98% maximum O2 uptake (VO2max) was varied between 0.5 and 6 min before measurement of maximal STPO.

As PE duration increased subsequent STPO fell to approximately 70% of control values after 3-6 min. In series ii the effect of varying the intensity of PE of fixed 6-min duration was studied in five subjects. After PE less than 60% VO2max there was an increase of 12% in STPO, but after greater than 60% VO2max there was a progressive fall in STPO as PE intensity increased, indicating a reduction of approximately 35% at 100% VO2max compared with control values. In series iii we examined the effect on STPO of allowing a recovery period after a fixed intensity (mean = 87% VO2max) of 6 min PE before measurement of STPO. This indicated a rapid recovery of dynamic function with a half time of approximately 32 s, which is similar to the kinetics of PC resynthesis and taken with the other findings suggests the dominant role that PC exerts on the STPO under these conditions.

Fatigue in sprint cycling exercise due to type II muscle fibres

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This important study shows how depletion of the energy source for sprint exercise is depleted and remains depleted after a bout of sprint exercise lasting for 25 seconds. The study was part of the PhD work of the talented Christina Karatzaferi working under the direction of Professor Tony Sargeant.
Pflugers Archiv
Pflugers Arch. 2001 Jun;442(3):467-74

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.