Anthony J. Sargeant

In vivo measurements of the triceps surae complex architecture in man: implications for muscle function

1 The objectives of this study were to (1) quantify experimentally in vivo changes in pennation angle, fibre length and muscle thickness in the triceps surae complex in man in response to changes in ankle position and isometric plantarflexion moment and (2) compare changes in the above muscle architectural characteristics occurring in the transition from rest to a given isometric plantarflexion intensity with the estimations of a planimetric muscle model assuming constant thickness and straight muscle fibres. 2 The gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and soleus (SOL) muscles of six males were scanned with ultrasonography at different sites along and across the muscle belly at rest and during maximum voluntary contraction (MVC) trials at ankle angles of −15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg. Additional images were taken at 80, 60, 40 and 20 % of MVC at an ankle angle of 0 deg. 3 In all three muscles and all scanned sites, as ankle angle increased from −15 to +30 deg, pennation increased (by 6–12 deg, 39–67 %, P < 0.01 at rest and 9–16 deg, 29–43 %, P < 0.01 during MVC) and fibre length decreased (by 15–28 mm, 32–34 %, P < 0.01 at rest and 8–10 mm, 27–30 %, P < 0.05 during MVC). Thickness in GL and SOL increased during MVC compared with rest (by 5–7 mm, 36–47 %, P < 0.01 in GL and 6–7 mm, 38–47 %, P < 0.01 in SOL) while thickness of GM did not differ (P > 0.05) between rest and MVC. 4 At any given ankle angle the model underestimated changes in GL and SOL occurring in the transition from rest to MVC in pennation angle (by 9–12 deg, 24–38 %, P < 0.01 in GL and 9–14 deg, 25–28 %, P < 0.01 in SOL) and fibre length (by 6–15 mm, 22–39 %, P < 0.01 in GL and 6–8 mm, 23–24 %, P < 0.01 in SOL). 5 The findings of the study indicate that the mechanical output of muscle as estimated by the model used may be unrealistic due to errors in estimating the changes in muscle architecture during contraction compared with rest.

Effect of muscle temperature on leg extension force and short-term power output in humans

SummaryThe effect of changing muscle temperature on performance of short term dynamic exercise in man was studied. Four subjects performed 20 s maximal sprint efforts at a constant pedalling rate of 95 crank rev · min−1 on an isokinetic cycle ergometer under four temperature conditions: from rest at room temperature; and following 45 min of leg immersion in water baths at 44; 18; and 12‡ C. Muscle temperature (Tm) at 3 cm depth was respectively 36.6, 39.3, 31.9 and 29.0‡ C. After warming the legs in a 44‡ C water bath there was an increase of ∼11% in maximal peak force and power (PPmax) compared with normal rest while cooling the legs in 18 and 12‡ C water baths resulted in reductions of ∼12% and 21% respectively. Associated with an increased maximal peak power at higher Tm was an increased rate of fatigue. Two subjects performed isokinetic cycling at three different pedalling rates (54, 95 and 140 rev · min−1) demonstrating that the magnitude of the temperature effect was velocity dependent: At the slowest pedalling rate the effect of warming the muscle was to increase PPmax by ∼2% per ‡ C but at the highest speed this increased to ∼10% per ‡ C.

Characterization of human skeletal muscle fibres according to the myosin heavy chains they express

SummaryUsing a method of single muscle fibre analysis, we investigated the presence of RNA transcripts for various isoforms of the myosin heavy chain (MyoHC) gene in histochemically, immunohistochemically and electrophoretically characterized individual muscle fibres (n=65) from adult human vastus lateralis muscle. A cDNA clone isolated in this study was shown to contain the 3′ end of a previously uncharacterized human MyoHC gene which is expressed specifically in human fast IIA muscle fibres and we conclude that this clone contains part of the human fast IIA MyoHC gene. In all the fibres histochemically, immunohistochemically and electrophoretically characterized as containing the previously classified IIB MyoHC (n=23), it was shown that the human equivalent to the rat type IIX MyoHC gene is expressed. This observation was taken to suggest that the previously classified IIB muscle fibres in human muscle express a MyoHC isoform equivalent to the rat IIX, not the IIB, and would therefore be more accurately classified as IIX fibres.

Changes in Achilles tendon moment arm from rest to maximum isometric plantarflexion: in vivo observations in man

1 The purpose of the present study was to examine the effect of a plantarflexor maximum voluntary contraction (MVC) on Achilles tendon moment arm length. 2 Sagittal magnetic resonance (MR) images of the right ankle were taken in six subjects both at rest and during a plantarflexor MVC in the supine position at a knee angle of 90 deg and at ankle angles of ‐30 deg (dorsiflexed direction), ‐15 deg, 0 deg (neutral ankle position), +15 deg (plantarflexed direction), +30 deg and +45 deg. A system of mechanical stops, support triangles and velcro straps was used to secure the subject in the above positions. Location of a moving centre of rotation was calculated for ankle rotations from ‐30 to 0 deg, ‐15 to +15 deg, 0 to +30 deg and +15 to +45 deg. All instant centres of rotation were calculated both at rest and during MVC. Achilles tendon moment arms were measured at ankle angles of ‐15, 0, +15 and +30 deg. 3 At any given ankle angle, Achilles tendon moment arm length during MVC increased by 1‐1.5 cm (22‐27 %, P < 0.01) compared with rest. This was attributed to a displacement of both Achilles tendon by 0.6‐1.1 cm (P < 0.01) and all instant centres of rotation by about 0.3 cm (P < 0.05) away from their corresponding resting positions. 4 The findings of this study have important implications for estimating loads in the musculoskeletal system. Substantially unrealistic Achilles tendon forces and moments generated around the ankle joint during a plantarflexor MVC would be calculated using resting Achilles tendon moment arm measurements.

Non‐linear relationship between O2 uptake and power output at high intensities of exercise in humans.

1. A slow component to pulmonary oxygen uptake (VO2) is reported during prolonged high power exercise performed at constant power output at, or above, approximately 60% of the maximal oxygen uptake. The magnitude of the slow component is reported to be associated with the intensity of exercise and to be largely accounted for by an increased VO2 across the exercising legs. 2. On the assumption that the control mechanism responsible for the increased VO2 is intensity dependent we hypothesized that it should also be apparent in multi‐stage incremental exercise tests with the result that the VO2‐power output relationship would be curvilinear. 3. We further hypothesized that the change in the VO2‐power output relationship could be related to the hierarchical recruitment of different muscle fibre types with a lower mechanical efficiency. 4. Six subjects each performed five incremental exercise tests, at pedalling rates of 40, 60, 80, 100 and 120 rev min‐1, over which range we expected to vary the proportional contribution of different fibre types to the power output. Pulmonary VO2 was determined continuously and arterialized capillary blood was sampled and analysed for blood lactate concentration ([lactate]b). 5. Below the level at which a sustained increase in [lactate]b was observed pulmonary VO2 showed a linear relationship with power output; at high power outputs, however, there was an additional increase in VO2 above that expected from the extrapolation of that linear relationship, leading to a positive curvilinear VO2‐power output relationship. 6. No systematic effect on the magnitude or onset of the ‘extra’ VO2 was found in relation to pedalling rate, which suggests that it is not related to the pattern of motor unit recruitment in any simple way.

In vivo specific tension of human skeletal muscle

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.

Temperature Effect on the Rates of Isometric Force Development and Relaxation in the Fresh and Fatigued Human Adductor Pollicis Muscle

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.

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

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.

Human muscle function following prolonged eccentric exercise

Summary4 subjects performed repeated eccentric contractions with leg extensors during prolonged downhill walking (−25% gradient) at 6.44 km · h−1 until collapse due to muscle weakness (range of exercise duration 29 to 40 min). During the exercise oxygen uptake rose progressively from ∼45% of the previously determined