Do habitual foot-strike patterns in running influence functional Achilles tendon properties during gait?

The capacity of foot-strike running patterns to influence the functional properties of the Achilles tendon is controversial. This study used transmission-mode ultrasound to investigate the influence of habitual running foot-strike pattern on Achilles tendon properties during barefoot walking and running. Fifteen runners with rearfoot (RFS) and 10 with a forefoot (FFS) foot-strike running pattern had ultrasound transmission velocity measured in the right Achilles tendon during barefoot walking (≈1.1 ms-1) and running (≈2.0 ms-1). Temporospatial gait parameters, ankle kinematics and vertical ground reaction force were simultaneously recorded. Statistical comparisons between foot-strike patterns were made using repeated measure ANOVAs. FFS was characterised by a significantly shorter stance duration (-4%), greater ankle dorsiflexion (+2°), and higher peak vertical ground reaction force (+20% bodyweight) than RFS running (P < .05). Both groups adopted a RFS pattern during walking, with only the relative timing of peak dorsiflexion (3%), ground reaction force (1-2%) and peak vertical force loading rates (22-23%) differing between groups (P < .05). Peak ultrasound transmission velocity in the Achilles tendon was significantly higher in FFS during walking (≈100 ms-1) and running (≈130 ms-1) than RFS (P < .05). Functional Achilles tendon properties differ with habitual footfall patterns in recreational runners.

Tendinopathy alters ultrasound transmission in the patellar tendon during squatting.

Measurement of loading patterns of the patellar tendon during activity is important in understanding tendon injury. We used transmission-mode ultrasonography to investigate patellar tendon loading during squatting in adults with and without tendinopathy. It was hypothesized that axial ultrasonic velocity, a surrogate measure of the elastic modulus of tendon, would be lower in tendinopathy. Ultrasound velocity was measured in both patellar tendons of adults with unilateral patellar tendinopathy (n = 9) and in healthy controls (n = 16) during a bilateral squat maneuver. Sagittal knee movement was measured simultaneously with an electrogoniometer. Statistical comparisons between healthy and injured tendons were made using two-way mixed-design ANOVAs. Axial ultrasound velocity in both symptomatic and asymptomatic patellar tendons in tendinopathy was approximately 15% higher than in healthy tendons at the commencement (F1,23  = 5.2, P < 0.05) and completion (F1,23  = 4.5, P < 0.05) of the squat. While peak velocity was ≈5% higher during both flexion (F1,23  = 5.4, P < 0.05) and extension (F1,23  = 5.3, P < 0.05) phases, there was no significant between-group difference at the midpoint of the movement. There were no significant differences in the rate and magnitude of knee movement between groups. Although further research is required, these findings suggest enhanced baseline muscle activity in patellar tendinopathy and highlight fresh avenues for its clinical management.

Achilles tendon loading patterns during barefoot walking and slow running on a treadmill: An ultrasonic propagation study.

Measurement of tendon loading patterns during gait is important for understanding the pathogenesis of tendon "overuse" injury. Given that the speed of propagation of ultrasound in tendon is proportional to the applied load, this study used a noninvasive ultrasonic transmission technique to measure axial ultrasonic velocity in the right Achilles tendon of 27 healthy adults (11 females and 16 males; age, 26 ± 9 years; height, 1.73 ± 0.07 m; weight, 70.6 ± 21.2 kg), walking at self-selected speed (1.1 ± 0.1 m/s), and running at fixed slow speed (2 m/s) on a treadmill. Synchronous measures of ankle kinematics, spatiotemporal gait parameters, and vertical ground reaction forces were simultaneously measured. Slow running was associated with significantly higher cadence, shorter step length, but greater range of ankle movement, higher magnitude and rate of vertical ground reaction force, and higher ultrasonic velocity in the tendon than walking (P < 0.05). Ultrasonic velocity in the Achilles tendon was highly reproducible during walking and slow running (mean within-subject coefficient of variation < 2%). Ultrasonic maxima (P1, P2) and minima (M1, M2) were significantly higher and occurred earlier in the gait cycle (P1, M1, and M2) during running than walking (P < 0.05). Slow running was associated with higher and earlier peaks in loading of the Achilles tendon than walking.

The open window of susceptibility to infection after acute exercise in healthy young male elite athletes.

The 'open window' theory is characterised by short term suppression of the immune system following an acute bout of endurance exercise. This window of opportunity may allow for an increase in susceptibility to upper respiratory illness (URI). Many studies have indicated a decrease in immune function in response to exercise. However many studies do not indicate changes in immune function past 2 hours after the completion of exercise, consequently failing to determine whether these immune cells numbers, or importantly their function, return to resting levels before the start of another bout of exercise. Ten male 'A' grade cyclists (age 24.2 +/- 5.3 years; body mass 73.8 +/- 6.5 kg; VO2peak 65.9 +/- 7.1 mL x kg(-1) x min(-1)) exercised for two hours at 90% of their second ventilatory threshold. Blood samples were collected pre-, immediately post-, 2 hours, 4 hours, 6 hours, 8 hours, and 24 hours post-exercise. Immune variables examined included total leukocyte counts, neutrophil function (oxidative burst and phagocytic function), lymphocyte subset counts (CD4+, CD8+, and CD16+/56+), natural killer cell activity (NKCA), and NK phenotypes (CD56dimCD16+, and CD56(bright)CD16-). There was a significant increase in total lymphocyte numbers from pre-, to immediately post-exercise (p < 0.01), followed by a significant decrease at 2 hours post-exercise (p < 0.001). CD4+ T-cell counts significantly increased from pre-exercise, to 4 hours post- (p < 0.05), and 6 hours post-exercise (p < 0.01). However NK (CD16+/56+) cell numbers decreased significantly from pre-exercise to 4 h post-exercise (p < 0.05), to 6 h post-exercise (p < 0.05), and to 8 h post-exercise (p < 0.01O). In contrast, CD56(bright)CD16- NK cell counts significantly increased from pre-exercise to immediately post-exercise (p < 0.01). Neutrophil oxidative burst activity did not significantly change in response to exercise, while neutrophil cell counts significantly increased from pre-exercise, to immediately postexercise (p < 0.05), and 2 hours post-exercise (p < 0.01), and remained significantly above pre-exercise levels to 8 hours post-exercise (p < 0.01). Neutrophil phagocytic function significantly decreased from 2 hours post-exercise, to 6 hours post- (p < 0.05), and 24 hours post-exercise (p < 0.05). Finally, eosinophil cell counts significantly increased from 2 hours post to 6 hours post- (p < 0.05), and 8 hours post-exercise (p < 0.05). This is the first study to show changes in immunological variables up to 8 hours post-exercise, including significant NK cell suppression, NK cell phenotype changes, a significant increase in total lymphocyte counts, and a significant increase in eosinophil cell counts all at 8 hours post-exercise. Suppression of total lymphocyte counts, NK cell counts and neutrophil phagocytic function following exercise may be important in the increased rate of URI in response to regular intense endurance training.

Anthropometry profiles of elite rugby players: quantifying changes in lean mass.

OBJECTIVE: To demonstrate the utility of a practical measure of lean mass for monitoring changes in the body composition of athletes. METHODS: Between 1999 and 2003 body mass and sum of seven skinfolds were recorded for 40 forwards and 32 backs from one Super 12 rugby union franchise. Players were assessed on 13 (7) occasions (mean (SD)) over 1.9 (1.3) years. Mixed modelling of log transformed variables provided a lean mass index (LMI) of the form mass/skinfolds(x), for monitoring changes in mass controlled for changes in skinfold thickness. Mean effects of phase of season and time in programme were modelled as percentage changes. Effects were standardised for interpretation of magnitudes. RESULTS: The exponent x was 0.13 for forwards and 0.14 for backs (90% confidence limits +/-0.03). The forwards had a small decrease in skinfolds (5.3%, 90% confidence limits +/-2.2%) between preseason and competition phases, and a small increase (7.8%, 90% confidence limits +/-3.1%) during the club season. A small decrease in LMI (approximately 1.5%) occurred after one year in the programme for forwards and backs, whereas increases in skinfolds for forwards became substantial (4.3%, 90% confidence limits +/-2.2%) after three years. Individual variation in body composition was small within a season (within subject SD: body mass, 1.6%; skinfolds, 6.8%; LMI, 1.1%) and somewhat greater for body mass (2.1%) and LMI (1.7%) between seasons. CONCLUSIONS: Despite a lack of substantial mean changes, there was substantial individual variation in lean mass within and between seasons. An index of lean mass based on body mass and skinfolds is a potentially useful tool for assessing body composition of athletes.

Mechanisms underlying stabilization of temporally summated muscle contractions in the lobster (Panulirus) pyloric system.

Muscles are the final effectors of behavior. The neural basis of behavior therefore cannot be completely understood without a description of the transfer function between neural output and muscle contraction. To this end, we have been studying muscle contraction in the well-investigated lobster pyloric system. We report here the mechanisms underlying stabilization of temporally summating contractions of the very slow dorsal dilator muscle in response to motor nerve stimulation with trains of rhythmic shock bursts at a physiological intraburst spike frequency (60 Hz), physiological cycle periods (0.5-2 s), and duty cycles from 0.1 to 0.8. For temporal summation to stabilize, the rise and relaxation amplitudes of the phasic contractions each burst induces must equalize as the rhythmic train continues. Stabilization could occur by changes in rise duration, rise slope, plateau duration, and/or relaxation slope. We demonstrate a generally applicable method for quantifying the relative contribution changes in these characteristics make to contraction stabilization. Our data show that all characteristics change as contractions stabilize, but their relative contribution differs depending on stimulation cycle period and duty cycle. The contribution of changes in rise duration did not depend on period or duty cycle for the 1-, 1.5-, and 2-s period regimes, contributing approximately 30% in all cases; but for the 0.5-s period regime, changes in rise duration increased from contributing 25% to contributing 50% as duty cycle increased from 0.1 to 0.8. At all cycle periods decreases in rise slope contributed little to stabilization at small duty cycles but increased to contributing approximately 80% at high duty cycles. The contribution of changes in plateau duration decreased in all cases as duty cycle increased; but this decrease was greater in long cycle period regimes. The contribution of changes in relaxation slope also decreased in all cases as duty cycle increased; but for this characteristic, the decrease was greatest in fast cycle period regimes, and in these regimes at high duty cycles these changes opposed contraction stabilization. Exponential fits to contraction relaxations showed that relaxation time constant increased with total contraction amplitude; this increase presumably underlies the decreased relaxation slope magnitude seen in high duty cycle, fast cycle period regimes. These data show that changes in no single contraction characteristic can account for contraction stabilization in this muscle and suggest that predicting muscle response in other systems in which slow muscles are driven by rapidly varying neuronal inputs may be similarly complex.

Muscles express motor patterns of non-innervating neural networks by filtering broad-band input.

We describe three slow muscles that responded to low-frequency modulation of a high-frequency neuronal input and, consequently, could express the motor patterns of neural networks whose neurons did not directly innervate the muscles. Two of these muscles responded to different frequency components present in the same input, and as a result each muscle expressed the motor pattern of a different, non-innervating, neural network. In an analogous manner, the distinct dynamics of the multiple intracellular processes that most cells possess may allow each process to respond to, and hence differentiate among, specific frequency ranges present in broad-band input.

Motor neuron activity is often insufficient to predict motor response.

Our understanding of the necessity of considering peripheral properties when investigating how neural activity generates behavior has significantly increased in recent years. These advances include a theoretical analysis of the neuromuscular transform and a deeper understanding of the functional effects of non-linear contractile responses, slow muscle relaxation, and neuromodulation.

Physiological and psychometric variables for monitoring recovery during tapering for major competition.

PURPOSE: This study attempted to identify variables that are useful in monitoring recovery during tapering. METHODS: Changes in physiological variables, tethered swimming force, mood states, and self-ratings of well-being were measured in 10 elite swimmers from before to after 2 wk of tapering for national championships. Physiological measures included resting heart rate (HR); blood pressure (BP); blood lactate concentration; red blood cell, white blood cell, and differential counts; and plasma cortisol, free testosterone, and catecholamine concentrations. Measures taken after 100-m maximal and 200-m standardized submaximal swims included HR, BP, and blood lactate concentration. RESULTS: Step-down regression analysis showed that changes in plasma norepinephrine concentration, heart rate after maximal effort swimming and confusion as measured by the Profile of Mood States (POMS) predicted the change in swimming time with tapering (r2 = 0.98); the change in plasma norepinephrine concentration predicted the change in swim time with tapering (r2 = 0.82) by itself. CONCLUSION: These data suggest that recovery after intense training can be monitored during tapering and that an accurate prediction of performance changes may be possible if the changes in a range of physiological and psychological variables are measured.

Effects of three tapering techniques on the performance, forces and psychometric measures of competitive swimmers.

The 100-m and 400-m swim time, tethered swimming forces, mood states and self-ratings of well-being of 27 competitive swimmers were measured before and after 4 weeks of intense training and after 1 week and 2 weeks of tapering for major competition. The swimmers were divided into three groups. Each group completed one of three taper regimes similar to those currently performed by swimmers in preparation for competition: (a) reduced training frequency according to each athlete's daily ratings of well-being, (b) reduced training volume, and (c) reduced training volume and intensity. Significant improvements in the Profile of Mood States measures of tension, depression and anger (P < 0.05) were observed after 1 week of tapering, with significant improvements in total mood disturbance and fatigue (P < 0.05) and peak tethered swimming force (P < 0.01) after 2 weeks. Non-significant improvements in 100-m and 400-m swim time (P > 0.05) were observed and no significant differences were revealed among the three tapering techniques. These data highlighted the importance of providing sufficient recovery before competition, since 1 week of reduced training was not long enough to maximise the benefits of tapering. However, none of the three types of tapering currently used by competitive swimmers could be shown to be more beneficial than the others.

Muscle response to changing neuronal input in the lobster (Panulirus interruptus) stomatogastric system: slow muscle properties can transform rhythmic input into tonic output.

Slow, non-twitch muscles are widespread in lower vertebrates and invertebrates and are often assumed to be primarily involved in posture or slow motor patterns. However, in several preparations, including some well known invertebrate "model" preparations, slow muscles are driven by rapid, rhythmic inputs. The response of slow muscles to such inputs is little understood. We are investigating this issue with a slow stomatogastric muscle (cpv1b) driven by a relatively rapid, rhythmic neural pattern. A simple model suggests that as cycle period decreases, slow muscle contractions show increasing intercontraction temporal summation and at steady state consist of phasic contractions overlying a tonic contracture. We identify five components of these contractions: total, average, tonic, and phasic amplitudes, and percent phasic (phasic amplitude divided by total amplitude). cpv1b muscle contractions induced by spontaneous rhythmic neural input in vitro consist of phasic and tonic components. Nerve stimulation at varying cycle periods and constant duty cycle shows that a tonic component is always present, and at short periods the muscle transforms rhythmic input into almost completely tonic output. Varying spike frequency, spike number, and cycle period show that frequency codes total, average, and tonic amplitudes, number codes phasic amplitude, and period codes percent phasic. These data suggest that tonic contraction may be a property of slow muscles driven by rapid, rhythmic input, and in these cases it is necessary to identify the various contraction components and their neural coding. Furthermore, the parameters that code these components are interdependent, and control of slow muscle contraction is thus likely complex.

Transduction of temporal patterns by single neurons.

As our ability to communicate by Morse code illustrates, nervous systems can produce motor outputs, and identify sensory inputs, based on temporal patterning alone. Although this ability is central to a wide range of sensory and motor tasks, the ways in which nervous systems represent temporal patterns are not well understood. I show here that individual neurons of the lobster pyloric network can integrate rhythmic patterned input over the long times (hundreds of milliseconds) characteristic of many behaviorally relevant patterns, and that their firing delays vary as a graded function of the pattern's temporal character. These neurons directly transduce temporal patterns into a neural code, and constitute a novel biological substrate for temporal pattern detection and production. The combined activities of several such neurons can encode simple rhythmic patterns, and I provide a model illustrating how this could be achieved.

Muscle response to changing neuronal input in the lobster (Panulirus interruptus) stomatogastric system: spike number- versus spike frequency-dependent domains.

We aimed to determine the neuronal parameters controlling the contraction of slowly contracting, non-twitch ("tonic") muscles driven by rhythmic neuronal activity. These muscles are almost completely absent in mammals but are common in lower vertebrates and invertebrates. Slow muscles are often believed to function primarily in tonic motor patterns. However, previous research and data presented here indicate that slow muscles are also driven by rhythmic neuronal inputs. In rapidly contracting "twitch" muscles, motor unit force is believed to be primarily determined by motor neuron spike frequency. What determines slow muscle output is less well understood. We present a simple model that suggests that when motor neuron burst duration is brief compared with muscle summation time, spike number, not spike frequency, determines slow muscle contraction amplitude. We present analyses that distinguish between spike number and spike frequency dependence in two slow muscles in the lobster stomatogastric system. Our analysis shows that, functionally, one muscle is spike number dependent, whereas the other is primarily spike frequency dependent. Thus, both of these parameters can determine slow muscle output. To predict the movements elicited by neuronal activity in preparations in which slow muscles are common, it may be necessary to determine spike number versus spike frequency dependence for each muscle. Spike number dependence couples motor neuron burst duration and spike frequency in that changing either parameter alone alters spike number (and hence muscle contraction amplitude). Neural networks innervating spike number-dependent muscles may therefore have specific properties to compensate for the complexity intrinsic to spike number coding.

The pyloric pattern of the lobster (Panulirus interruptus) stomatogastric ganglion comprises two phase-maintaining subsets.

The pyloric pattern approximately maintains phase over a three- to fivefold frequency range when the pattern is defined by the pacemaker burst beginning. However, in this reference frame certain pattern elements maintain phase better than others, which suggests phase-maintaining subgroups might exist. Reanalysis of these data in reference frames defined by each element shows the pattern contains two groups of pattern elements within which phase is well maintained but between which maintenance is relatively poor. A third element shows intermediate maintenance with each group. If ventricular dilator neuron burst beginning (VDB) is chosen as pattern beginning, all members of one group occur early in the pattern, all members of the other occur late in the pattern, and the intermediate element occurs between the groups. Thus, at least for phase maintenance, VDB is a "natural" pyloric pattern beginning. These results suggest full description of complex patterns is best achieved by analysis in many reference frames.

Phase maintenance in the pyloric pattern of the lobster (Panulirus interruptus) stomatogastric ganglion.

The extent to which individual neural networks can produce phase-constant motor patterns as cycle frequency is altered has not been studied extensively. I investigated this issue in the well-defined, rhythmic pyloric neural network. When pyloric cycle frequency is altered three- to fivefold, pyloric inter-neuronal delays shift by hundreds to thousands of msec, and all pyloric pattern elements show strong phase maintenance. The experimental paradigm used is unlikely to activate exogenous inputs to the network, and these delay changes are thus likely to arise from phase-compensatory mechanisms intrinsic to the network. Pyloric inter-neuronal delays depend on the time constants of the network's synapses and of the membrane properties of its neurons. The observed delay shifts thus suggest that, in response to changes in overall cycle frequency, these constants vary so as to maintain pattern phasing.

Hormonal, immunological, and hematological responses to intensified training in elite swimmers.

The purpose of this study was to compare the responses of selected hormonal, immunological, and hematological variables in athletes showing symptoms of overreaching with these variables in well-trained athletes during intensified training. Training volume was progressively increased over 4 wk in 24 elite swimmers (8 male, 16 female); symptoms of overreaching were identified in eight swimmers based on decrements in swim performance, persistent high ratings of fatigue, and comments in log books indicating poor adaptation to the increased training. Urinary excretion of norepinephrine was significantly lower (P < 0.05, post hoc analysis) in overreached (OR) compared with well-trained (WT) swimmers throughout the 4 wk. There were no significant differences between OR and WT swimmers for other variables including: concentrations of plasma norepinephrine, cortisol, and testosterone, and the testosterone/cortisol ratio; peripheral blood leukocyte and differential counts, neutrophil/lymphocyte ratio, and CD4/CD8 cell ratio; serum ferritin and blood hemoglobin concentrations, erythrocyte number, hematocrit, and mean red cell volume (MCV). MCV increased significantly over the 4 wk in both groups, suggesting increased red blood cell turnover. These data show that, of the 16 hormonal, immunological, and hematological variables measured, urinary norepinephrine excretion appears to be the only one to distinguish OR from WT swimmers during short-term intensified training. Low urinary norepinephrine excretion was observed 2 to 4 wk before the appearance of symptoms of overreaching, suggesting the possibility that neuroendocrine changes may precede, and possibly contribute to, development of the overreaching/overtraining syndromes.

Plasma glutamine and upper respiratory tract infection during intensified training in swimmers.

The purposes of this study were to determine the effects of 4 wk of intensified training on resting plasma glutamine concentration, and to determine whether changes in plasma glutamine concentration relate to the appearance of upper respiratory tract infection (URTI) in swimmers during intensified training. Resting plasma glutamine concentration was measured by high performance liquid chromatography in 24 elite swimmers (8 male, 16 female, ages 15-26 yr) during 4 wk of intensified training (increased volume). Symptoms of overtraining syndrome (OT) were identified in eight swimmers (2 male, 6 female) based on decrements in swim performance and persistent high fatigue ratings; non-overtrained subjects were considered well-trained (WT). Ten of 24 swimmers (42%, 1 OT and 9 WT) exhibited URTI during the study. Plasma glutamine concentration increased significantly (P = 0.04, ANOVA) over the 4 wk, but the increase was significant only in WT swimmers (P < 0.05, post-hoc analysis). Compared with WT, plasma glutamine was significantly lower in OT at the mid-way timepoint only (P < 0.025, t-test with Bonferroni correction). There was no significant difference in glutamine levels between athletes who developed URTI and those who did not. These data suggest that plasma glutamine levels may not necessarily decrease during periods of intensified training, and that the appearance of URTI is not related to changes in plasma glutamine concentration in overtrained swimmers.

Markers for monitoring overtraining and recovery.

Physiological and mood state parameters were monitored during a 6-month swimming season in an attempt to determine markers of overtraining and recovery. Fourteen elite male and female swimmers were tested early-, mid-, and late-season and shortly before and after major competition. Training details and subjective ratings of well-being were compiled by the athletes in daily logs. Three swimmers were classified as stale based upon performance deterioration and prolonged, high fatigue levels. Staleness scores were calculated for each athlete using performance change from early- to late-season and daily fatigue ratings for the season. Regression analysis revealed a battery of well-being ratings which predicted staleness scores, accounting for 76% of the variance. The late-season stress ratings and plasma catecholamine levels at rest predicted staleness scores, accounting for 85% of the variance. During tapering, well-being ratings predicted improvement in competitive performance, accounting for 72% of the variance of the improvement in race times from previous best times. It was concluded that self-reported ratings of well-being may provide an efficient means of monitoring both overtraining and recovery; plasma catecholamine levels at rest may provide an additional objective tool for diagnosis.