Effects of plyometric training on both active and passive parts of the plantarflexors series elastic component stiffness of muscle-tendon complex

The aims of this study were to determine the effects of plyometric training on both active and passive parts of the series elastic component (SEC) stiffness, and on geometrical parameters [i.e., muscle architecture, muscle and tendon cross-sectional area (CSA)] of the plantarflexors muscle–tendon complex to assess possible specific adaptations of the elastic properties. Nineteen subjects were randomly divided into a trained group and a control group. Active and passive components of the SEC stiffness were determined using a fast stretch during submaximal voluntary isometric plantarflexor activity. Geometrical parameters of the triceps surae muscles and the Achilles tendon were determined using ultrasonography. A significant increase in the passive component of the SEC stiffness was found (p < 0.05). In contrast, a significant decrease in the active part of the SEC stiffness was observed (p < 0.05). No significant changes in plantarflexor muscles CSA, architecture and Achilles tendon CSA were seen (p > 0.05). Thus, plyometric training led to specific adaptations within each part of the SEC. Theses adaptations could increase both the efficiency of the energy storage–recoil process and muscular tension transmission leading to an increase in jump performances.     

Effect of cold water immersion on 100-m sprint performance in well-trained swimmers

The aim of the present study was to examine the effect of cold water immersion (CWI) on sprint swimming performance in simulated competition conditions. Ten well-trained swimmers (5 males, 5 females; 19.0 ± 3.9 years) performed two 100-m swimming sprints (S1 and S2) interspersed with a 30-min passive recovery period, during which athletes were randomly assigned to 5 min of CWI (14°C) or an out-of-water control condition (CON 28°C). During tests, sprint times, heart rate (HR), pre- and post-race parasympathetic activity via HR variability (natural logarithm of the square root of the mean of the sum of the squares of differences between adjacent normal R–R intervals; Ln rMSSD) and blood lactate accumulation ([La]_ac) and clearance ([La]_cle) were recorded. Rates of perceived recovery (RPR) and exertion (RPE) were evaluated before and after each sprint. CWI was associated with a ‘likely’ decrease in swimming performance [1.8% (90% CI 0.2, 3.5)], as well as ‘likely’ lower peak HR [−1.9% (−3.6, −0.2)]. CWI was also associated with a ‘likely’ smaller decrease in Ln rMSSD after the first sprint [−16.7% (−30.9, −4.1)]. RPR was ‘likely’ better [+27.2% (−3.7, 68.0)] following CWI. ‘unclear’ effects were observed for [La]_ac [+24.7% (−13.4, 79.5)], [La]_cle [−7.6% (−24.2, 12.7)] or RPE [+2.0% (−12.3, 18.5)]. Following CWI, changes in sprint times were ‘largely’ correlated with changes in peak HR (r = 0.80). Despite a subjective perception of improved recovery following CWI, this recovery intervention resulted in slower swimming times in well-trained athletes swimming in simulated competition conditions.     

Association of muscle hardness with muscle tension dynamics: a physiological property

This study aimed to investigate the relationship between muscle hardness and muscle tension in terms of length–tension relationship. A frog gastrocnemius muscle sample was horizontally mounted on the base plate inside a chamber and was stretched from 100 to 150% of the pre-length, in 5% increments. After each step of muscle lengthening, electrical field stimulation for induction of tetanus was applied using platinum-plate electrodes positioned on either side of the muscle submerged in Ringer’s solution. The measurement of muscle hardness, i.e., applying perpendicular distortion, was performed whilst maintaining the plateau of passive and tetanic tension. The relationship between normalised tension and normalised muscle hardness was evaluated. The length–hardness diagram could be created from the modification with the length–tension diagram. It is noteworthy that muscle hardness was proportional to passive and total tension. Regression analysis revealed a significant correlation between muscle hardness and passive and total tension, with a significant positive slope (passive tension: r = 0.986, P < 0.001; total tension: r = 0.856, P < 0.001). In conclusion, our results suggest that muscle hardness depends on muscle tension in most ranges of muscle length in the length–tension diagram.     

Is passive stiffness in human muscles related to the elasticity of tendon structures?

The purpose of this study was to examine in vivo whether passive stiffness in human muscles was related to the elasticity of tendon structures and to performance during stretch-shortening cycle exercise. Passive torque of plantar flexor muscles was measured during passive stretch from 90° (anatomical position) to 65° of dorsiflexion at a constant velocity of 5°·s^–1. The slope of the linear portion of the passive torque-angle curve during stretching was defined as the passive stiffness of the muscle. The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured using ultrasonography during ramp isometric plantar flexion up to the voluntary maximum. The relationship between the estimated muscle force of MG and tendon elongation was fitted to a linear regression, the slope of which was defined as the stiffness of the tendon. In addition, the dynamic torques during maximal voluntary concentric plantar flexion with and without prior eccentric contraction were determined at a constant velocity of 120°·s^–1. There were no significant correlations between passive stiffness and either the tendon stiffness (r=0.19, P>0.05) or the relative increase in torque with prior eccentric contraction (r=–0.19, P>0.05). However, tendon stiffness was negatively correlated to the relative increase in torque output (r=–0.42, P<0.05). The present results suggested that passive stiffness was independent of the elasticity of tendon structures, and had no favourable effect on the muscle performance during stretch-shortening cycle exercise. Electronic Publication     

Insertion of α1S II–III loop and C terminal sequences into α1H fails to restore excitation–contraction coupling in dysgenic myotubes

The L-type Ca²⁺ channel in skeletal muscle (α_1S) is essential for excitation–contraction (EC) coupling. Previous studies using chimeras composed of α_1S together with α_1C or α_1M demonstrated the importance of the α_1S II–III loop and of a smaller subdomain (residues 720–764; ‘ECC’) in skeletal EC coupling. However, these chimeras failed to test the significance of regions outside the II–III loop, which are highly conserved between α_1S and α_1C. Therefore, we have injected dysgenic (α_1S-lacking) myotubes with cDNAs encoding chimeras between α_1S and the highly divergent T-type Ca²⁺ channel, α_1H. The chimeras consisted of GFP-tagged α_1H with one or more of the following substitutions: α_1S II–III loop residues 720–764 (‘ECC’), a putative targeting domain of the α_1S C terminus (‘target’; residues 1543–1662) or the entire α_1S C terminus (‘Cterm’; residues 1382–1873). The presence of either target or Cterm affected the expression and/or kinetics of whole-cell currents recorded from both dysgenic muscle cells and tsa-201 cells. Importantly, substitution of ECC alone into GFP-α_1H (GFP-α_1H + ECC), or together with either target (GFP-α_1H + ECC + target) or Cterm (GFP-α_1H + ECC + Cterm ), was insufficient to restore electrically evoked contractions. Depolarization-induced fluorescence transients for GFP-α_1H + ECC, GFP-α_1H + ECC + target or GFP-α_1H + ECC + Cterm had a bell shaped dependence upon membrane voltage (inconsistent with skeletal EC coupling) and were also exceedingly small (unlike cardiac EC coupling). The absence of EC coupling for these chimeras raises the possibility that regions of α_1S outside of ECC and target are necessary for providing the context that allows these two domains to function in EC coupling and targeting, respectively. Additionally, an inadequate membrane density of the chimeras may have contributed to the lack of coupling. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of the tendon in the dynamic performance of three different load-moving muscles

The effect of the tendon's viscoelastic properties on the dynamic performance of three different load-moving muscles was determined. The frequency response models of the cat's medial gastrocnemius (MG), extensor digitorum longus (EDL), and tibialis anterior (TA) with and without their tendons were derived under sinusoidal shortening-lengthening, manipulated by orderly recruitment and derecruitment of motor units together with firing rate increase and decrease. The passive load sizes applied to the muscles were approximately 30%–40% of each muscle's maximal isometric force. It was shown that the tendon has a moderate effect on the dynamic response of muscles while moving loads of fixed mass. The MG and EDL without their tendons show a decrease in high frequency gain (2–5 dB) and increasing phase lag angles (7°–9°). In contrast, the TA without its tendon shows an increase in high frequency gain (2 dB) and decreasing phase lag angles (20°) compared with the same muscle with the tendon. It was concluded that tendon's viscoelastic properties have a moderate effect during load-moving contractions, influencing the dynamic performance of different muscles in a different manner.     

Aerobic power and peak power of elite America’s Cup sailors

Big-boat yacht racing is one of the only able bodied sporting activities where standing arm-cranking (‘grinding’) is the primary physical activity. However, the physiological capabilities of elite sailors for standing arm-cranking have been largely unreported. The purpose of the study was to assess aerobic parameters, VO_2peak and onset of blood lactate (OBLA), and anaerobic performance, torque–crank velocity and power–crank velocity relationships and therefore peak power (P _max) and optimum crank-velocity (ω_opt), of America’s Cup sailors during standing arm-cranking. Thirty-three elite professional sailors performed a step test to exhaustion, and a subset of ten grinders performed maximal 7 s isokinetic sprints at different crank velocities, using a standing arm-crank ergometer. VO_2peak was 4.7 ± 0.5 L/min (range 3.6–5.5 L/min) at a power output of 332 ± 44 W (range 235–425 W). OBLA occurred at a power output of 202 ± 31 W (61% of W_max) and VO₂ of 3.3 ± 0.4 L/min (71% of VO_2peak). The torque–crank velocity relationship was linear for all participants (r = 0.9 ± 0.1). P _max was 1,420 ± 37 W (range 1,192–1,617 W), and ω_opt was 125 ± 6 rpm. These data are among the highest upper-body anaerobic and aerobic power values reported. The unique nature of these athletes, with their high fat-free mass and specific selection and training for standing arm cranking, likely accounts for the high values. The influence of crank velocity on peak power implies that power production during on-board ‘grinding’ may be optimised through the use of appropriate gear-ratios and the development of efficient gear change mechanisms.     

Pulmonary O₂ uptake and muscle deoxygenation kinetics are slowed in the upper compared with lower region of the moderate-intensity exercise domain in older men

This study sought to determine the effect of the pre-transition work rate (WR) and WR transition magnitude on the adjustment of pulmonary oxygen uptake (VO_2p kinetics) in older men. Seven men (69 ± 5 years; mean ± SD) each performed 4–6 cycling transitions from 20 W to either a WR corresponding to 90% estimated lactate threshold (full step, FS) or 2 equal-step transitions (lower step, LS; upper step, US) to the same end-exercise WR as in FS. Gas exchange was analysed breath-by-breath and muscle deoxygenation (∆[HHb]) was measured with NIRS. The time constant (τ) for VO_2p was greater in US (53 ± 17 s) and FS (44 ± 11 s) compared to LS (37 ± 9 s); τVO_2p for US also trended (p = 0.05) towards being greater than FS. The VO_2p gain in US (9.97 ± 0.41 mL/min/W) was greater than LS (9.06 ± 1.17; p = 0.06) and FS (9.13 ± 0.54; p < 0.05). The O₂ deficit was greater in US (0.25 ± 0.08 L) than LS (0.19 ± 0.06 L); yet the ‘accumulated O₂ deficit’ (0.44 ± 0.13 L; O₂ deficit from LS + US) was similar to that of FS (0.42 ± 0.13 L; p = 0.38). The effective Δ[HHb] response time (τ′∆[HHb]) for US (36 ± 12 s) was greater than LS (27 ± 6 s; p = 0.07) and FS (26 ± 4 s; p < 0.05), suggesting that the slowed adjustment of muscle O₂ extraction was associated with the slowed VO₂ kinetics of the US. Despite already slowed VO_2p kinetics, older men exhibit further slowing when small WR transitions are initiated from an elevated pre-transition WR, yet this results in no cumulative impact on O₂ deficit. This slowing in US compared to LS does not appear to be related to local O₂ availability.     

Effect of series elasticity on isokinetic torque-angle relationship in humans

The influence of muscle series elasticity on the relationship between torque and joint angle during dynamic contractions was studied. The torque–angle relationship during the maximal isokinetic knee extension was determined for six male subjects (25–45 years) at 0.52, 1.05, 1.57, 2.09, 2.62, 3.49 rad/s. The knee joint angle at which peak torque was observed showed a systematic shift to more extended positions, i.e., the quadriceps muscle–tendon unit length became shorter as the velocity increased [from 1.01 (0.12) rad (0.52 rad/s) to 0.75 (0.14) rad (3.49 rad/s), mean (SD)]. The corresponding difference in muscle–tendon unit length between 0.52 and 3.49 rad/s, estimated from the angle shift at peak torque and the moment arm length change of the quadriceps muscles, was 9 (4) mm. The relationship between estimated changes in muscle–tendon unit length and muscle force of the vastus lateralis and intermedius (VLI) over the seven velocities (including isometric contraction, 0 rad/s) coincided with the load-elongation properties of the series elastic component of VLI, determined separately in vivo by ultrasonography when the same subjects performed a ramp isometric knee extension. The results suggest that the torque–angle relationship is affected by the interaction between contractile and elastic components, and that peak torque angle shift is attributable to the elongation of tendinous tissues as a function of force applied to them. Electronic Publication     

Passive repetitive loading of the lumbar tissues influences force output and EMG during maximal efforts

Loading of the low back tissues induces tension-relaxation in the viscoelastic connective tissues. The extent to which repetitive loading influences the muscle activation and subsequent muscle force production has not been fully explored. The purpose of this study was to examine the myoelectric activity of the trunk muscles during maximal flexion and extension exertions before and after a passive trunk flexion–extension protocol. Nineteen subjects performed three trials of maximal efforts in trunk flexion and extension while seated in an upright position. Surface electromyography (EMG) recordings were collected bilaterally from paraspinal (thoracic, TP, lumbar LP), rectus abdominis (RA), and external oblique muscles. A 10-minute passive trunk flexion–extension protocol was used to repetitively load the lumbar tissues at a rate of 0.17 rad/s, through the subjects’ range of motion. The main findings included a significant reduction in moment output during extension efforts (p < 0.05) with significant reductions in the average EMG from the TP and LP muscles during extension (p < 0.05). In flexion, peak and average EMGs were also significantly reduced (p < 0.05). The results indicate a significant reduction in the ability of the trunk extensors to output force, but this may be due to the increased compliance of the connective tissues rather than modified neuromuscular signals to the paraspinal muscles. However, neuromuscular changes were apparent in the TP and RA muscles suggesting a modified control mechanism was present.     

Muscle deoxygenation to VO₂ relationship differs in young subjects with varying τVO₂

The relationship between the adjustment of muscle deoxygenation (∆[HHb]) and phase II VO_2p was examined in subjects presenting with a range of slow to fast VO_2p kinetics. Moderate intensity VO_2p and ∆[HHb] kinetics were examined in 37 young males (24 ± 4 years). VO_2p was measured breath-by-breath. Changes in ∆[HHb] of the vastus lateralis muscle were measured by near-infrared spectroscopy. VO_2p and ∆[HHb] response profiles were fit using a mono-exponential model, and scaled to a relative % of the response (0–100%). The ∆[HHb]/∆VO_2p ratio for each individual (reflecting the matching of O₂ distribution to O₂ utilization) was calculated as the average ∆[HHb]/∆VO_2p response from 20 to 120 s during the exercise on-transient. Subjects were grouped based on individual phase II VO_2p time-constant (τVO_2p): <21 s [very fast (VF)]; 21–30 s [fast (F)]; 31–40 s [moderate (M)]; >41 s [slow (S)]. The corresponding ∆[HHb]/∆VO_2p were 0.98 (VF), 1.05 (F), 1.09 (M), and 1.22 (S). The larger ∆[HHb]/∆VO_2p in the groups with slower VO_2p kinetics resulted in the ∆[HHb]/∆VO_2p displaying a transient “overshoot” relative to the subsequent steady state level, which was progressively reduced as τVO₂ became smaller (r = 0.91). When τVO_2p > ~20 s, the rate of adjustment of phase II VO_2p appears to be mainly constrained by the matching of local O₂ distribution to muscle VO₂. These data suggest that in subjects with “slower” VO₂ kinetics, the rate of adjustment of VO₂ may be constrained by O₂ availability within the active tissues related to the matching of microvascular O₂ distribution to muscle O₂ utilization.     

Kinetics of VO2 limb blood flow and regional muscle deoxygenation in young adults during moderate intensity, knee-extension exercise

The kinetics of pulmonary O₂ uptake ( [(V)\dot]\textO _2 \textp ), \left( {\dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} } \right), limb blood flow (LBF) and deoxygenation (ΔHHb) of the vastus lateralis (VL) and vastus medialis (VM) muscles during the transition to moderate-intensity knee-extension exercise (MOD) was examined. Seven males (27 ± 5 years; mean ± SD) performed repeated step transitions (n = 4) from passive exercise to MOD. Breath by breath [(V)\dot]\textO _2 \textp , \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} , femoral artery LBF, and VL and VM muscle ∆HHb were measured, respectively, by mass spectrometer and volume turbine, Doppler ultrasound and near-infrared spectroscopy. Phase 2 [(V)\dot]\textO _2 \textp , \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} , LBF, and ∆HHb data were fit with a mono-exponential model. The time constant (τ) of the [(V)\dot]\textO _2 \textp \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} and LBF response were not different ( t[(V)\dot]\textO _2 \textp , \tau \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} , 24 ± 6 s; τLBF, 23 ± 8 s). The ∆HHb response did not differ between VL and VM in amplitude (VL 6.97 ± 4.22 a.u.; VM 7.24 ± 3.99 a.u.), time delay (∆HHb_TD: VL 17 ± 2 s; VM 15 ± 1 s), time constant (τ∆HHb: VL 11 ± 6 s; VM 13 ± 4 s), or effective time constant [τ′∆HHb (= ∆HHb_TD + τ∆HHb): VL 28 ± 7 s; VM 28 ± 4 s]. Adjustments in ∆HHb in VL and VM depict a similar balance of regional O₂ delivery and utilization within the quadriceps muscle group. The τ′∆HHb and t[(V)\dot]\textO _2 \textp \tau \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} were similar, however, the ∆HHb displayed an “overshoot” relative to the steady-state levels reflecting a slower alteration of microvascular blood flow (O₂ delivery) relative to O₂ utilization, necessitating a greater reliance on O₂ extraction.     

Impact of Pregnancy and Vaginal Delivery on the Passive and Active Mechanics of the Rat Vagina

Remodeling of vaginal extracellular matrix and smooth muscle likely plays a critical role in reducing the risk of maternal injury during vaginal delivery by altering the mechanical properties to increase distension and reduce stress. Long-Evans rats were divided into five groups to examine the passive mechanical and active contractile properties throughout pregnancy and postpartum: virgin (n = 17), mid-pregnant (Day 14–16, n = 12), late-pregnant (Day 20–22, n = 14), immediate postpartum (0–2 h after delivery, n = 14), and 4 week postpartum (n = 15). Longitudinal sections of vaginal tissue were loaded to failure uniaxially for passive mechanical or active contractile properties were examined. For passive mechanics, the tangent modulus decreased 45% by mid-pregnancy and immediately postpartum (p < 0.001). The ultimate strain continuously increased up to 43% higher than virgin animals (p = 0.007) in the immediate postpartum group. For active mechanics, the maximal contractile force was 36–56% lower through immediate postpartum animals, and was significantly more sensitive to K⁺ throughout pregnancy and postpartum (p = 0.003). The changes observed in the passive and active properties of the rat vagina are consistent with what would be expected from a tissue that is remodeling to maximize its ability to distend at the time of vaginal delivery to facilitate passage of the fetus with minimal injury.     

Muscle architecture and passive lengthening properties of the gastrocnemius medialis and Achilles tendon in children who idiopathically toe-walk

Children who idiopathically toe-walk (ITW) habitually operate at greater plantarflexion angles and thus, at shorter muscle-tendon unit (MTU) lengths than typically developing (TD) children. Therefore, it is often assumed that habitual use of the gastrocnemius muscle in this way will cause remodelling of the muscle-tendon architecture compared to TD children. However, the gastrocnemius muscle architecture of children who ITW has never been measured. It is essential that we gain a better understanding of these muscle-tendon properties, to ensure that appropriate clinical interventions can be provided for these children. Five children who ITW (age 8 ± 2 years) and 14 TD children (age 10 ± 2 years) participated in this study. Ultrasound was combined with isokinetic dynamometry and surface electromyography, to measure muscle architecture at common positions and passive lengthening properties of the gastrocnemius muscle and tendon across full range of motion. Regardless of which common condition groups were compared under, both the absolute and normalised to MTU muscle belly and fascicle lengths were always longer, and the Achilles tendon length was always shorter in children who ITW than TD children (p < 0.05; large effect sizes). The passive lengthening properties of the muscle and tendon were not different between groups (p > 0.05); however, passive joint stiffness was greater in children who ITW at maximum dorsiflexion (p = 0.001) and at a joint moment common to all participants (p = 0.029). Consequently, the findings of this pilot study indicate a remodelling of the relative MTU that does not support the concept that children who ITW commonly experience muscle shortening. Therefore, greater consideration of the muscle and tendon properties are required when prescribing clinical interventions that aim to lengthen the MTU, and treatments may be better targeted at the Achilles tendon in children who ITW.     

Neonatal control of nutritive sucking pressure: evidence for an intrinsic τ-guide

 Human newborns appear to regulate sucking pressure when bottle feeding by employing, with similar precision, the same principle of control evidenced by adults in skilled behavior, such as reaching (Lee et al., 1998a). In particular, the present study of 12 full-term newborn infants indicated that the intraoral sucking pressures followed an internal dynamic prototype – an intrinsic τ-guide. The intrinsic τ-guide, a recent hypothesis of general tau theory is a time-varying quantity, τ_g, assumed to be generated within the nervous system. It corresponds to some quantity (e.g., electrical charge), changing with a constant second-order temporal derivative from a rest level to a goal level, in the sense that τ_g equals τ of the gap between the quantity and its goal level at each time t. (τ of a gap is the time-to-closure of the gap at the current closure-rate.) According to the hypothesis, the infant senses τ_p, the τ of the gap between the current intraoral pressure and its goal level, and regulates intraoral pressure so that τ_p and τ_g remain coupled in a constant ratio, k; i.e., τ_p=kτ_g. With k in the range 0–1, the τ-coupling would result in a bell-shaped rate of change pressure profile, as was, in fact, found. More specifically, the high mean r ² values obtained when regressing τ_p on τ_g, for both the increasing and decreasing suction periods of the infants’ suck, supported a strong τ-coupling between τ_p and τ_g. The mean k values were significantly higher in the increasing suction period, indicating that the ending of the movement was more forceful, a finding which makes sense given the different functions of the two periods of the suck. Received: 2 October 1997 / Accepted: 26 August 1998     

Salivary antimicrobial peptides (LL-37 and alpha-defensins HNP1–3), antimicrobial and IgA responses to prolonged exercise

There are many factors in mucosal secretions that contribute to innate immunity and the ‘first line of defence’ at mucosal surfaces. Few studies, however, have investigated the effects of exercise on many of these ‘defence’ factors. The aim of the present study was to determine the acute effects of prolonged exercise on salivary levels of selected antimicrobial peptides (AMP) that have not yet been studied in response to exercise (HNP1–3 and LL-37) in addition to immunoglobulin A (IgA). A secondary objective was to assess the effects of exercise on saliva antibacterial capacity. Twelve active men exercised on a cycle ergometer for 2.5 h at ~60% of maximal oxygen uptake. Unstimulated whole saliva samples were obtained before and after exercise. There was a significant decrease (P < 0.05) in salivary IgA:osmolality ratio, following exercise, but IgA concentration and secretion rate were unaltered. Salivary HNP1–3 and LL-37 concentrations (P < 0.01 and P < 0.05, respectively), concentration:osmolality ratios (P < 0.01) and secretion rates (P < 0.01) all increased following exercise. Salivary antibacterial capacity (against E. coli) did not change. The increased concentration of AMPs in saliva may confer some benefit to the ‘first line of defence’ and could result from synergistic compensation within the mucosal immune system and/or airway inflammation and epithelial damage. Further study is required to determine the significance of such changes on the overall ‘defence’ capacity of saliva and how this influences the overall risk for infection.     

Association Between Polymorphisms of the Dopamine Receptor D2 and Catechol-o-Methyl Transferase Genes and Cognitive Function

The dopaminergic neurotransmitter system of the brain is involved in working memory and other cognitive functions. Studies suggest an important role for dopamine synthesis and uptake in modulation of human cognitive processes. We studied the association between polymorphisms in the catechol-o-methyl transferase (COMT) and dopamine receptor D2 (DRD2) genes and general cognitive ability in a secondary analysis of 2091 men and women, aged 55–80 years living in Scotland. General cognitive ability ‘g’ was derived from five cognitive tests of different domains. COMT was not associated with cognitive ability in this population. The DRD2 C:C genotype of rs6277 was associated with decreased general cognitive ability ‘g’ (p = 0.003), and DRD2 rs1800497 heterozygotes had lowest mean general cognitive ability ‘g’ (p = 0.007). There was an indication of a potential interaction between the DRD2 SNPs.     

Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans

[(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , [(Q)\dot] \dot{Q} and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%_VT) and at 120% of [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (120%_Wmax). An innovative approach was applied to calculate the time constant (τ₂) of the primary phase of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(Q)\dot] \dot{Q} kinetics at 120%_Wmax. Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , \mathop Q ^· \mathop Q\limits^{ \cdot } and HHb data were fitted with traditional exponential models. τ₂ of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was longer (62.5 ± 20.9 s) at 120%_Wmax than at 80%_VT (27.8 ± 10.4 s). The τ₂ of [(Q)\dot] \dot{Q} kinetics was unaffected by exercise intensity and, at 120% of [(V)\dot]\textO_2max , \dot{V}{\text{O}}_{2\max } , it was significantly faster (τ₂ = 35.7 ± 28.4 s) than that of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%_Wmax than at 80%_VT (8.5 ± 2.6 s) suggesting a larger mismatch between O₂ uptake and delivery at 120%_Wmax. These results suggest that [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} at the onset of exercise is not regulated/limited by muscle’s O₂ utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics observed during supramaximal exercise.     

Age Differences in Genetic and Environmental Variations in Stress-Coping During Adulthood: A Study of Female Twins

The way people cope with stressors of day to day living has an important influence on health. The aim of the present study was to explore whether genetic and environmental variations in stress-coping differ over time during adulthood. The brief COPE was mailed to a large sample of the UK female twins (N = 4,736) having a wide range of age (20–87 years). Factor analyses of the items of the brief COPE yielded three coping scales: ‘Problem-Solving’, ‘Support Seeking’, and ‘Avoidance’. Monozygotic and dizygotic twin correlations tended to become lower with age for all three scales, suggesting that unique environmental factors may become more important with age during adulthood. Model-fitting results showed that relative influences of unique environmental factors increased from 60 % at age 20 years to 74% at age 87 years for ‘Problem-Solving’ and 56 % at age 20 years to 76% at age 87 years for ‘Avoidance’. During the same age period, genetic factors decreased from 40 to 26 % for ‘Problem-Solving’ and from 44 to 24 % for ‘Avoidance’. For ‘Seeking Support’, the magnitude of genetic and unique environmental factors was not significantly different across the adulthood. For all three scales, shared environmental effects were negligible. Overall, our findings implicate that the effects of environment that stem from idiosyncratic experience of stressful life events accumulate and become increasingly important in adulthood.