Freely chosen pedal rate during free cycling on a roller and ergometer cycling

The purpose of this study was to examine the effect of regulation of work rate, computer controlled versus controlled by the subject, on the relationship between work rate, freely chosen pedal rate (FCC) and gross efficiency. Eighteen male cyclists participated in the study. One group, freely cycling (FC) on a competition bike mounted on an electromagnetic roller, could use gearing and cadence to achieve each work rate. The other group (EC) was cycling on an ergometer which enables a constant work rate, independent of cadence. Subjects performed an increasing work rate protocol from 100 W up to exhaustion. We found a strong interaction between group and work rate on cadence (P < 0.001). In the FC group, work rate affected cadence (P < 0.001), increasing from 72 rpm at 100 W to 106 rpm at 350 W. For the EC group, no work rate effect was present (average FCC 92 rpm). Gross efficiency increased with work rate for both groups. The efficiency–cadence relationship was strongly affected by the protocol. At a given work rate, very similar efficiency values were obtained at highly different cadences. The discrepancy in the FCC-work rate relationship between the EC group and the FC group may be related to the manner in which one can regulate work rate. FCC depends not only on work rate but is also affected considerably by the manner in which the work rate can be controlled by cadence. This finding may have important implications for the interpretation of the preferred pedaling rate, especially how this is related to optimizing metabolic cost.     

Determinants of maximal cycling power: crank length, pedaling rate and pedal speed

The purpose of this investigation was to determine the effects of cycle crank length on maximum cycling power, optimal pedaling rate, and optimal pedal speed, and to determine the optimal crank length to leg length ratio for maximal power production. Trained cyclists (n=16) performed maximal inertial load cycle ergometry using crank lengths of 120, 145, 170, 195, and 220 mm. Maximum power ranged from a low of 1149 (20) W for the 220-mm cranks to a high of 1194 (21) W for the 145-mm cranks. Power produced with the 145- and 170-mm cranks was significantly (P<0.05) greater than that produced with the 120- and 220-mm cranks. The optimal pedaling rate decreased significantly with increasing crank length, from 136 rpm for the 120-mm cranks to 110 rpm for the 220-mm cranks. Conversely, optimal pedal speed increased significantly with increasing crank length, from 1.71 m/s for the 120-mm cranks to 2.53 m/s for the 220-mm cranks. The crank length to leg length and crank length to tibia length ratios accounted for 20.5% and 21.1% of the variability in maximum power, respectively. The optimal crank length was 20% of leg length or 41% of tibia length. These data suggest that pedal speed (which constrains muscle shortening velocity) and pedaling rate (which affects muscle excitation state) exert distinct effects that influence muscular power during cycling. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults. Electronic Publication     

Muscle fibre type,efficiency, and mechanical optima affect freely chosen pedal rate during cycling

This study investigated the variation in freely chosen pedal rate between subjects and its possible dependence on percentage myosin heavy chain I (%MHC I) in m. vastus lateralis, maximum leg strength and power, as well as efficiency. Additionally, the hypothesis was tested that a positive correlation exists between percentage MHC I and efficiency at pre‐set pedal rates but not at freely chosen pedal rate. Twenty males performed cycling at low and high submaximal power output (～40 and 70% of the power output at which maximum oxygen uptake (VO_2max) was attained at 80 r.p.m.) with freely chosen and pre‐set pedal rates (61, 88, and 115 r.p.m.). Percentage MHC I as well as leg strength and power were determined. Freely chosen pedal rate varied considerably between subjects: 56–88 r.p.m. at low and 61–102 r.p.m. at high submaximal power output. This variation was only partly explained by percentage MHC I (21–97%) as well as by leg strength and power. Interestingly, %MHC I correlated significantly with the pedal rate at which maximum peak crank power occurred (r = ?0.81). As hypothesized, %MHC I and efficiency were unrelated at freely chosen pedal rate, which was in contrast to a significant correlation found at pre‐set pedal rates (r = 0.61 and r = 0.57 at low and high power output, respectively). Conclusions: Subjects with high percentage MHC I chose high pedal rates close to the pedal rates at which maximum peak crank power occurred, while subjects with low percentage MHC I tended to choose lower pedal rates, favouring high efficiency. Nevertheless, the considerable variation in freely chosen pedal rate between subjects was neither fully accounted for by percentage MHC I nor by leg strength and power. Previously recognized relationships between percentage Type I (～%MHC I) and efficiency as well as between pedal rate and efficiency were confirmed for pre‐set pedal rates, but for freely chosen pedal rate, these variables were unrelated.     

Effects of standing cycling and the use of toe stirrups on maximal oxygen uptake

Summary Twenty-eight subjects (6 normal men, 14 distance runners, and 8 rowers) were tested for maximal oxygen uptake ( ) and associated physiological measures during bicycle ergometer exercise with toe stirrups while standing (BEts) and during treadmill exercise (TM). Correlation between BEts and TM was high (r=0.901, p<0.05). No significant difference existed between the two values (60.3±8.9 vs. 60.5±9.7 ml · kg⁻¹ · min⁻¹; n=28). No differences were found even when three different subgroups were separately compared. It is concluded that the higher elicited during BEts as compared with normal sitting cycling may be attributed to the increased muscle blood flow and/ or involvement of a larger muscle mass, the latter being partly evidenced by the observation of greater electrornyographic activity during BEts.     

Muscle fibre type,efficiency, and mechanical optima affect freely chosen pedal rate during cycling

This study investigated the variation in freely chosen pedal rate between subjects and its possible dependence on percentage myosin heavy chain I (%MHC I) in m. vastus lateralis, maximum leg strength and power, as well as efficiency. Additionally, the hypothesis was tested that a positive correlation exists between percentage MHC I and efficiency at pre-set pedal rates but not at freely chosen pedal rate. Twenty males performed cycling at low and high submaximal power output ( approximately 40 and 70% of the power output at which maximum oxygen uptake (VO(2max)) was attained at 80 r.p.m.) with freely chosen and pre-set pedal rates (61, 88, and 115 r.p.m.). Percentage MHC I as well as leg strength and power were determined. Freely chosen pedal rate varied considerably between subjects: 56-88 r.p.m. at low and 61-102 r.p.m. at high submaximal power output. This variation was only partly explained by percentage MHC I (21-97%) as well as by leg strength and power. Interestingly, %MHC I correlated significantly with the pedal rate at which maximum peak crank power occurred (r = -0.81). As hypothesized, %MHC I and efficiency were unrelated at freely chosen pedal rate, which was in contrast to a significant correlation found at pre-set pedal rates (r = 0.61 and r = 0.57 at low and high power output, respectively). Conclusions: Subjects with high percentage MHC I chose high pedal rates close to the pedal rates at which maximum peak crank power occurred, while subjects with low percentage MHC I tended to choose lower pedal rates, favouring high efficiency. Nevertheless, the considerable variation in freely chosen pedal rate between subjects was neither fully accounted for by percentage MHC I nor by leg strength and power. Previously recognized relationships between percentage Type I ( approximately %MHC I) and efficiency as well as between pedal rate and efficiency were confirmed for pre-set pedal rates, but for freely chosen pedal rate, these variables were unrelated.     

Additional manal and pedal epiphyseal centres.

One hundred and thirty-six well-preserved medieval skeletons were excavated in advance of re-development in Norwich. Examination of sub-adult hand and feet bones indicated a high percentage of accessory epiphyses. The majority could be identified by traces of a fusion line. The distal first metacarpal and first metatarsal being the preferred sites. Such additional epiphyses have rarely been reported in archaeological samples and the findings are in strong contrast to the figures quoted in modern anatomical texts. The possible reasons for this apparent variation are discussed.     

Relationship between postural balance and knee and toe muscle power in young women

Muscle power in the lower extremities and body sway were measured in 57 healthy young women volunteers in their 20's. Body sway was measured with a stabilimeter for 30 sec during two-leg standing, and for 10 sec during one-leg standing with the eyes open or closed, alternating between right and left legs (5 times each). The measured parameters of body sway were locus length per time unit, locus length per environmental area, environmental area, rectangle area, root mean square area, and the ratio of sway with eyes closed to sway with eyes open. Knee flexor and extensor power and toe flexor and abductor power were the measures representing lower extremity muscle power. The increase in sway with the eyes closed was more marked during one-leg standing than two-leg standing, as expected. We found that 36 of 57 subjects (62%) were unable to maintain one-leg standing with their eyes closed, and this failure correlated with marked body sway (P = 0.0086). Many subjects had one leg that was classified as stable and the other leg classified as unstable. Clearly, testing of both legs alternately with eyes closed is necessary to measure the full range of sway in subjects. Lower extremity muscle power did not appear to be the dominant factor in maintaining balance in these young subjects.     

Control of pedal and parapodial movements in Aplysia. II. Cerebral ganglion neurons.

1. Intracellular stimulation of individual neurons in the two symmetrical A neuron clusters of the cerebral ganglion evoked contractions of both the foot and parapodia. Electrical stimulation of pedal and parapodial nerves caused antidromic action potentials in A neurons. Units recorded in the nerves followed the driven somatic spike 1:1. This suggests that the A neurons are presumptive pedal and parapodial motor neurons.2. Individual A neurons evoked both bilteral and unilateral contractions of the parapodia or split foot. Contractions in the parapodia were independent of those in the foot. An individual A neuron caused contractions in either the foot or the parapodia, but not both. Sequential transection of parapodial nerves had only a slight effect until a key nerve was cut. The contractions produced by a single A neuron on one side were then abolished. These data suggest that the motor fields of the A neurons are well defined within the foot or the parapodia. 3. Parapodial contractions produced by individual A neurons are not dependent on the excitation of follower motor neurons. Blocking synaptic transmission by the addition of CoCl2 did not eliminate the contractions produced by driving individual A neurons. This is consistent with the A neurons being motor neurons. 4. Intracellular stimulation of individual neurons in the symmetrical B neuron clusters of the cerebral ganglion also evoked pedal and parapodial contractions. Electrical stimulation of the pedal and parapodial nerves elicited antidromic spikes in these neurons. Individual B neurons caused contractions in both the foot and parapodia. This suggests that the B neurons are motor neurons with very large motor fields. 5. Filling the pedal and parapodial nerves with cobalt primarily filled the cell bodies of neurons located in the pedal and pleural ganglia. The somata of A and B neurons were also occasionally filled. This is consistent with the electrophisiological results. 6. Other neurons also evoked parapodial contractions. Intracellular stimulation of neurons in the pedal and pleural ganglia caused parapodial contractions in intact animals. Some of these neurons were excited by stretching the parapodia or touching the tentacles. 7. The B neurons are strongly excited by tactile stimulation of the tentacles. Since they can cause pedal and parapodial contractions they may mediate reflex contractions elicited by tentacular stimulation. Stretching the parapodia only occasionally caused the A neurons to fire. This makes it unlikely that they make a major contribution to pedal and parapodial proprioceptive reflexes. These reflexes are probably controlled by neurons in the pedal and pleural ganglia.     

HIV1 cytopathogenicity-genetic difference between direct cytotoxic and fusogenic effect.

Formation of large syncytia, rapid cell killing, and early onset of replication are characteristics of the highly cytopathic Zairian virus strain HIV1 NDK compared with the HIV1 LAV prototype. Recombinant provirus molecules derived from cloned infectious DNAs of HIV1 LAV and NDK were constructed by reciprocal exchange of genetic material using conserved restriction sites. Different regions of the HIV1 genome were responsible for variability of the direct single-cell cytotoxic and fusogenic effects. A minimal, provisionally defined portion of genetic information responsible for the higher cytotoxicity of HIV1 NDK compared to the HIV1 LAV prototype was localized in the fragment Spel1042/EcoRl4183, containing the 3'-terminal half of gag and a majority of the pol gene. This region also determined the rapid replication properties of HIV1 NDK. The increased fusogenic potential of HIV1 NDK was associated with the simultaneous presence of HIV1 NDK fragments BssHll255/Spel1042 and EcoRl5278/Xhol8401 which contained the splicing donor, packaging sequence, p18 gag protein, and the HIV env gene. The increase in the direct killing effect but not in the syncytium forming ability of HIV1 NDK correlated with the early onset of replication and rapid spread of HIV1 NDK in cell cultures. The HIV1 NDK fragments BssHll/Spel and EcoRl/Xhol were by themselves necessary but not sufficient to induce formation of large syncytia.     

Mycobacterial peritonitis: difference between non-tuberculous mycobacteria and Mycobacterium tuberculosis

Unlike tuberculous peritonitis, peritonitis due to non-tuberculous mycobacteria (NTM) has unclear clinical manifestations. This study aimed to clarify the clinical manifestations and laboratory results of NTM peritonitis and compare it to tuberculous peritonitis. This retrospective study was conducted from 2000 to 2008 in a medical centre in Taiwan. Patients with mycobacteria isolated from ascites were identified and compared according to causative pathogens (Mycobacterium tuberculosis or NTM). Those with NTM peritonitis were further classified into the ‘probable’ and ‘possible’ groups based on diagnostic evidence. Twenty-five patients with NTM peritonitis and 65 with tuberculous peritonitis were reviewed. Mycobacterium avium complex was the most common NTM pathogen (52%). There was no obvious difference between the ‘probable’ and ‘possible’ NTM peritonitis groups regarding age and laboratory data. Patients with NTM peritonitis and those with tuberculous peritonitis had no differences in age or gender but varied in symptoms and serum laboratory data. NTM peritonitis was 100% associated with underlying co-morbidities and had lower proportions of lymphocytes and albumin level in ascites. Twelve (48%) NTM peritonitis and 21 (32%) tuberculous peritonitis patients died during the 6-month follow-up. Antimycobacterial treatment, but not mycobacterial species, was correlated with better 6-month survival. In Taiwan, NTM is responsible for 28% of mycobacterial peritonitis cases, which have a poor prognosis if untreated. There are some differences in clinical manifestations between NTM and tuberculous peritonitis. NTM peritonitis should be considered in patients with peritonitis but without causative microorganisms identified other than NTM.     

Clones of cytotoxic lymphocytes in culture: the difference in specificity between stimulated and nonstimulated cytotoxic lymphocytes.

The specificity of individual clones of cytotoxic lymphocytes (CL) which develop upon stimulation by semi-allogeneic cells, have been examined and compared with the specificity of CL clones which develop spontaneously when normal spleen cells are cultured without stimulator cells. It was found that the specificity of stimulated clones was different from the specificity of 'spontaneous' clones. Specifically stimulated clones from CBA cells cultured with (CBA x DBA)F1 stimulator cells, did not discriminate between the H2dP815 and H2dDBA splenic blast, and lysed both targets. In contrast, spontaneous CL clones from cultures of CBA or (CBA x DBA)F1 spleen cells were found to lyse either P815 or DBA blast, but not both. The results indicated that the spontaneous CL clones were not a representative sample of the the total pool of CL.     

Marked difference in electrophoretic migration rates between two influenza A viruses.

Comparative moving boundary electrophoresis revealed that influenza virus A/PR/8/34 (H0N1) has a 2.5 times higher electrophoretic migration rate at pH 7 than influenza virus A/Singpore/1/57 (H2N2). This difference was the same whether the compared viruses were purified first by either ammonium sulphate precipitation or adsorption onto and elution from red blood cells and then by density gradient centrifugation. The same electrophoretic methods was used for testing the homogeneity of influenza virus preparations purified by either method.     

GTP-related difference in cyclic AMP production between resident and inflammatory human peritoneal macrophages.

In macrophages cyclic AMP (c-AMP) plays an important role in regulating many activities such as phagocytosis, migration and tumoricidal activity. High intracellular levels of c-AMP are negatively correlated with these activities. In earlier studies we have shown that c-AMP levels in inflammatory human peritoneal macrophages (IM) were markedly lower when compared to levels in resident macrophages (RM). This is in line with the fact that c-AMP down-regulates macrophage activity. To our knowledge no data are available on the mechanism underlying the difference in c-AMP production between RM and IM. In this study the difference in c-AMP production between RM and IM has been investigated on the level of receptor and G-protein-related mechanisms. Macrophage membranes were incubated with different agents i.e. prostaglandin E2 (PGE2), prostacyclin I2 (PGI2), isoprenalin (ISO) and sodium fluoride (SF). Additionally, the capacity of IM and RM to hydrolyse quanosine triphosphate (GTP) was measured. Only in the presence of GTP (10(-4) M) could the c-AMP difference be detected (RM = 51 +/- 4.4 pmol/mg protein/min +/- S.E., n = 22, IM = 32.8 +/- 5.2 pmol/mg protein/min +/- S.E., n = 10, p less than 0.01). After receptor stimulation with PGE2, PGI2 and ISO, c-AMP levels increased to the same extent in both IM and RM with no effect on the GTP-related difference. After SF stimulation, c-AMP levels in RM and IM increased to the same level (RM = 63 +/- 8 pmol/mg protein/min, n = 14, IM = 58 +/- 11 pmol/mg protein/min, n = 13).(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms of restenosis after coronary intervention: difference between plain old balloon angioplasty and stenting.

BACKGROUND: Restenosis after coronary intervention remains an unsolved and important clinical problem. We histologically examined the mechanism of restenosis after both balloon injury and stenting. METHODS: Coronary arteries of swine were subjected to balloon injury and stenting. Next, just after stenting or at 7, 14, or 28 days, the animals were sacrificed for the evaluation by morphometric analysis, histological observation, and immunostaining. RESULTS: The neointimal area peaked at 14 days in the balloon injury group (BG) and increased linearly up to 28 days in the stent group (SG). At 28 days, the total vascular area in the BG was reduced to 78% of the control values. In the SG, the total vascular area remained enlarged. According to the phenotypic analysis, the vascular smooth muscle cells (VSMCs) in the neointimal area at 28 days were the contractile type in the BG and the synthetic type in the SG. Proliferating cell nuclear antigen (PCNA) and macrophage-positive cells were not observed in neointima in the BG at 28 days, whereas they were observed around the stent struts in the SG. In addition, numerous inflammatory cells, such as neutrophils and eosinophils, were also present in the SG. CONCLUSIONS: Restenosis after balloon injury consisted of arterial remodeling and neointimal hyperplasia, whereas that after stenting consisted mostly of neointimal hyperplasia. The neointimal area in the SG lasted longer than that in the BG. Continuous inflammation may be an important factor in the restenosis of stenting.     

Autonomic neuropathy and toe circulation. A prospective study

Ankle and toe pressure ratios and toe temperature reactions to cold followed by indirect heating were evaluated in 23 diabetic patients with and without autonomic neuropathy (AN) in a first and in a second follow-up study after 5-7 years. In the first study, despite normal blood pressure ratios, AN patients, all with parasympathetic neuropathy, showed a markedly delayed increase in toe temperature after cooling followed by indirect heating. In the second study, most AN patients showed sympathetic neuropathy and had higher toe temperatures before cooling than those without AN. Parasympathetic neuropathy leads to increased sensitivity to cold in toe vessels and sympathetic neuropathy to vasodilation and increased toe temperatures.