Quantifying Paddling Kinematics through Muscle Activation and Whole Body Coordination during Maximal Sprints of Different Durations on a Kayak Ergometer: A Pilot Study.

Paddling technique and stroke kinematics are important performance factors in flatwater sprint kayaking and entail significant energetic demands and a high strength from the muscles of the trunk and upper limbs. The various distances completed (from 200 m to 1000 m) require the athletes to optimize their pacing strategy, to maximize power output distribution throughout the race. This study aimed to characterize paddling technique and stroke kinematics during two maximal sprints of different duration. Nine nationally-trained participants (2 females, age: 18 ± 3 years; BMI: 22.2 ± 2.0 Kg m-1) performed 40 s and 4 min sprints at maximal intensity on a kayak ergometer. The main findings demonstrated a significantly greater mean stroke power (237 ± 80 W vs. 170 ± 48 W; p < 0.013) and rate (131 ± 8 spm vs. 109 ± 7 spm; p < 0.001) during the 40 s sprint compared to the 4 min sprint. Athletes used an all-out strategy for the 40 s exercise and a parabolic-shape strategy during the 4 min exercise. Despite the different strategies implemented and the higher muscular activation during the 40 s sprint, no change in paddling technique and body coordination occurred during the sprints. The findings of the present study suggest that the athletes constructed a well-defined profile that was not affected by fatigue, despite a decrease in power output during the all-out strategy. In addition, they regulated their paddling kinematics during the longer exercises, with no change in paddling technique and body coordination.

Effect of mental fatigue on speed-accuracy trade-off.

The aim of this study was to investigate the effects of mental fatigue on the duration of actual and imagined goal-directed arm movements involving speed-accuracy trade-off. Ten participants performed actual and imagined point-to-point arm movements as accurately and as fast as possible, before and after a 90-min sustained cognitive task inducing mental fatigue, and before and after viewing a neutral control task (documentary movie) that did not induce mental fatigue. Target width and center-to-center target distance were varied, resulting in five different indexes of difficulty. Prior to mental fatigue, actual and imagined movement duration increased with the difficulty of the task, as predicted by Fitts' law. Mental fatigue task induced a 4.1±0.7% increase in actual movement duration and a 9.6±1.1% increase in imagined movement duration, independently of the index of difficulty. The trial-by-trial evolution of actual and imagined movement duration remained stable with mental fatigue. The control task did not induce any change in actual and imagined movement duration. The results suggested that movement was slowed in the presence of mental fatigue, maybe due to proactive changes occurring during the preparatory state of the movement, to preserve task success.

Neuromuscular fatigue following isometric contractions with similar torque time integral.

Torque time integral (TTI) is the combination of intensity and duration of a contraction. The aim of this study was to compare neuromuscular alterations following different isometric sub-maximal contractions of the knee extensor muscles but with similar TTI. Sixteen participants performed 3 sustained contractions at different intensities (25%, 50%, and 75% of Maximal Voluntary Contraction (MVC) torque) with different durations (68.5±33.4 s, 35.1±16.8 s and 24.8±12.9 s, respectively) but similar TTI value. MVC torque, maximal voluntary activation level (VAL), M-wave characteristics and potentiated doublet amplitude were assessed before and immediately after the sustained contractions. EMG activity of the vastus lateralis (VL) and -rectus femoris (RF) muscles was recorded during the sustained contractions. MVC torque reduction was similar in the 3 conditions after the exercise (-23.4±2.7%). VAL decreased significantly in a similar extent (-3.1±1.3%) after the 3 sustained contractions. Potentiated doublet amplitude was similarly reduced in the 3 conditions (-19.7±1.5%), but VL and RF M-wave amplitudes remained unchanged. EMG activity of VL and RF muscles increased in the same extent during the 3 contractions (VL: 54.5±40.4%; RF: 53.1±48.7%). These results suggest that central and peripheral alterations accounting for muscle fatigue are similar following isometric contractions with similar TTI. TTI should be considered in the exploration of muscle fatigue during sustained isometric contractions.

Master triathletes have not reached limits in their Ironman triathlon performance.

The purpose of this study was to analyze the participation and performance trends of male triathletes in the "Ironman Switzerland" from 1995 to 2010. Participation trends of all finishers aged between 18 and 64 years were analyzed over the 16-year period by considering four 4-year periods 1995-1998, 1999-2002, 2003-2006, and 2007-2010, respectively. The 3.8-km swimming, 180-km cycling, 42-km running times, and total race times were analyzed for the top 10 triathletes in each age group from 18 to 64 years. The participation of master triathletes (≥40 years old) increased over the years, representing on average 23%, 28%, 37%, and 48% of total male finishers during the four 4-year periods, respectively. Over the 1995-2010 period, triathletes older than 40 years significantly improved their performance in swimming, cycling, running, and in the total time taken to complete the race. The question whether master Ironman triathletes have yet reached limits in their performance during Ironman triathlon should be raised. Further studies investigating training regimes, competition experience, or socio-demographic factors are needed to gain better insights into the phenomenon of the relative improvement in ultra-endurance performance with advancing age.

The age-related decline in Olympic distance triathlon performance differs between males and females.

AIM: The aim of this cross-sectional study was to compare the age-related declines in swimming, cycling, and running and overall race times between males and females in an Olympic distance triathlon, the 'Zürich Triathlon' in Switzerland. METHODS: Swimming (1.5 km), cycling (40 km), running (10 km) and overall race times of 7939 total finishers (1666 females and 6273 males) from 2000 to 2010 in the "Zürich Triathlon" were analysed. RESULTS: There was a significant (P<0.001) age effect on performance for both males and females independently of the discipline. No significant difference in the overall race time was observed between 18 and 34 years for both genders. There was an interaction (P<0.001) of age and gender for swimming, cycling and overall race times, but not for running times. The age-related declines in performance were significantly less pronounced for males compared with females for swimming (>50 years), for cycling (>40 years) and for overall race time (>40 years). CONCLUSION: These data suggest that the age and gender interactions in an Olympic distance triathlon performance differ between the three locomotion modes. Further studies investigating training regimes, competition experience or socio-demographic factors are needed to get a better insight in the phenomenon of the gender specific age-related declines in endurance performance.

Estimation of muscular fatigue under electromyostimulation using CWT.

The aim of this study is to investigate muscular fatigue and to propose a new fatigue index based on the continuous wavelet transform (CWT) which is compared to the standard fatigue indexes from literature. Fatigue indexes are all based on the electrical activity of muscles [electromyogram (EMG)] acquired during an electrically stimulated contraction thanks to two modules (electromyostimulation + electromyography recording) that can analyze EMG signals in real time during electromyostimulation. The extracted parameters are compared with each other and their sensitivity to noise is studied. The effect of truncation of M waves is then investigated, enlightening the robustness of the index obtained using CWT.

Physiological and cognitive responses when riding an electrically assisted bicycle versus a classical bicycle.

The present study compared the physiological responses and the subsequent cognitive performance when riding an electrically assisted (EB) versus a classical (CB) bicycle. Oxygen uptake, heart rate and leg extensor muscles electromyographic (EMG) activity were recorded in 10 subjects during a 30-min intermittent cycling exercise performed with EB versus CB. Cognitive performance was evaluated by a mail sorting test, performed at rest and after each cycling session. Averaged oxygen uptake and heat rate were significantly (P < 0.05) lower during EB cycling than during CB cycling. The EMG activities of the vastus lateralis, rectus femoris and gastrocnemius medialis muscles were significantly (P < 0.001) greater during CB cycling than during EB cycling. The time to complete the mail sorting test was significantly (P < 0.05) shorter after EB cycling than after CB cycling. Because EB cycling reduced muscle strains and physiological stress, it might offer benefits for those using bicycles in their work, such as postal workers and police officers. STATEMENT OF RELEVANCE: This study compared physiological and cognitive responses when riding an electrically assisted versus a classical bicycle. The results showed that the electrically assisted bicycle led to reduced muscle strains and physiological stress and, therefore, might offer benefits for those using bicycles in their work, such as postal workers and police officers.

Hip flexor muscle fatigue in patients with symptomatic femoroacetabular impingement.

PURPOSE: Patients with symptomatic femoroacetabular impingement (FAI) have considerable hip muscle weakness, in particular, hip flexion and hip adduction. In addition, they experience disabilities while performing prolonged dynamic tasks. It was therefore postulated that, besides hip flexor muscle weakness, patients with symptomatic FAI would show greater hip flexor fatigue compared with healthy controls. METHODS: Hip flexor fatigue was evaluated in two different experiments. Fifteen patients with symptomatic FAI and 15 age-matched healthy controls were tested in each experiment. In the first one, changes in hip flexor torque fluctuations and electromyographic (EMG) activity were measured during a sustained submaximal isometric contraction. In the second experiment, hip flexor torque decline was measured during a series of 20 maximal dynamic contractions. RESULTS: Patients with FAI exhibited hip flexor weakness under both isometric (P = 0.02) and isokinetic conditions (P = 0.03). Fatigue-induced changes in isometric hip flexor torque fluctuations, EMG root mean square and median frequency did not differ significantly between patients and controls (P > 0.05). Similarly, isokinetic hip flexor torque decline was comparable in patients with FAI and controls (P > 0.05). CONCLUSIONS: None of the hip flexor fatigue outcomes considered here differed between patients with symptomatic FAI and controls. Therefore, the disabilities that patients experience while performing prolonged dynamic tasks do not seem to be caused by exaggerated hip flexor muscle fatigue.

Participation and performance trends in ultra-triathlons from 1985 to 2009.

We examined the changes in participation and performance trends in ultra-triathlons, from the Double Iron (7.6 km swimming, 360 km cycling, 84.4 km running) to the Deca Iron (38 km swimming, 1800 km cycling, 422 km running), between 1985 (first year of a Double Iron) and 2009 (25 years). The mean finish rate for all distances and races was 75.8%. Women accounted for ∼8-10% of the ultra-triathlons starters. For Double and Triple Iron, the number of finishers per year increased, from 17 to 98 and from 7 to 41, respectively. In the Deca Iron, the finishers per race have remained <20 since the first event was held, up to 2009. Concerning World best performances, the men were ∼19% faster than the women in both the Double and Triple Iron, and ∼30% faster in a Deca Iron. With the increasing length of ultra-triathlons, the best women became relatively slower compared with the best men. Further investigations are required to understand why this gender difference in total performance time increased with the distance in ultra-triathlons.

Neuromuscular fatigue differs following unilateral vs bilateral sustained submaximal contractions.

The purpose of the present study was to compare the mechanisms of fatigue induced by a unilateral vs a bilateral submaximal isometric knee extension. Ten physically active men completed two experimental sessions, randomly presented. They were asked to maintain an isometric knee extension force corresponding to 20% of the maximal voluntary contraction (MVC) until task failure with one leg (unilateral) vs two legs (bilateral). MVCs were performed before and after the sustained contraction. Transcutaneous electrical stimuli were used to examine central (voluntary activation) and peripheral (peak doublet force at rest) fatigue on the exercised leg. Time to task failure was significantly shorter (P<0.05) for the bilateral (245 ± 76 s) compared with the unilateral task (295 ± 85 s). Unilateral MVC force and maximal voluntary activation losses were significantly greater (P<0.05) after the unilateral task than after the bilateral task. Peak doublet force was significantly reduced (P<0.01) after the unilateral task, but not after the bilateral task. The present results demonstrated that time to task failure of a submaximal fatiguing contraction may depend on the number of limbs involved in the task. The greater time to task failure with one leg may have induced greater contractile alterations and a larger MVC loss following the unilateral task.

A mixed FES/EMG system for real time analysis of muscular fatigue.

In this article, we present a functional electrical stimulator allowing the extraction in real time of M-wave characteristics from resulting EMG recodings in order to quantify muscle fatigue. This system is composed of three parts. A Labview software managing the stimulation output and electromyogram (EMG) input signal, a hardware part amplifying the output and input signal and a link between the two previous parts which is made up from input/output module (NIdaq USB 6251). In order to characterize the fatigue level, the Continuous Wavelet Transform is applied yielding a local maxima detection. The fatigue is represented on a scale from 0 for a fine shaped muscle to 100 for a very tired muscle. Premilary results are given.

Age-related changes in triathlon performances.

The aim of this study was two-fold: i) to analyse age-related declines in swimming, cycling, and running performances for Olympic and Ironman triathlons, and ii) to compare age-related changes in these three disciplines between the Olympic and Ironman triathlons. Swimming, cycling, running and total time performances of the top 10 males between 20 and 70 years of age (in 5 years intervals) were analysed for two consecutive world championships (2006 and 2007) for Olympic and Ironman distances. There was a lesser age-related decline in cycling performance (p<0.01) compared with running and swimming after 55 years of age for Olympic distance and after 50 years of age for Ironman distance. With advancing age, the performance decline was less pronounced (p<0.01) for Olympic than for Ironman triathlon in cycling (>55 years) and running (>50 years), respectively. In contrast, an age-related decline in swimming performance seemed independent of triathlon distance. The age-related decline in triathlon performance is specific to the discipline, with cycling showing less declines in performance with age than swimming and running. The magnitude of the declines in cycling and running performance at Ironman distance is greater than at Olympic distance, suggesting that task duration exerts an important influence on the magnitude of the age-associated changes in triathlon performance.

Influence of protein- versus carbohydrate-enriched feedings on physiological responses during an ultraendurance climbing race.

This study investigated effects of a high protein (PROT) versus a high carbohydrate (CHO) diet on performance and physiological responses during an ultraendurance climbing race at moderate altitude. On two different periods, in a randomised crossover design, ten climbers (30.0+/-0.9 years) participated in the race (duration 29 h approximately, energy expenditure 43.6+/-1.2 MJ.day (-1)) and were fed either with the PROT (30% protein content) or the CHO diet (68% carbohydrate) each providing 16.74 MJ. Mental performance was assessed by the Stroop test and we estimated maximal voluntary strength of quadriceps muscle. We quantified metabolic and hormonal circulating concentrations. Mental performance was unaffected after the two races, while muscular performance and body weight were decreased (both p<0.01) with no diet effects. Decreases were measured for IGF-I concentration and its binding protein IGFBP-3 (p<0.001), and increases for cortisol and norepinephrine (p<0.01) with no diet effects. Glucose concentration decreased (p<0.05) without diet effects, while amino acids (leucine, isoleucine, valine, and tyrosine) decreased in CHO group (p<0.001). Leptin concentration decreased (p<0.001) without diet effects, whereas total ghrelin increased in CHO group (p<0.01). Our results showed that a high PROT or high CHO intake during physical exertion at moderate altitude maintained mental performance, but did not limit muscle force reduction and body weight loss. There was decreased glucose availability, and hormonal responses indicated both catabolism and extreme energy deficiency induced by exercise with opposite responses of ghrelin and leptin. The ghrelin response was additionally indicative of macronutrient intake during the race.

Physiological stress monitoring of postmen during work.

The purpose of the present study was to characterize the physiological demands of postmen during a work day composed of mail sorting (inside work, IW) and cycling distribution (outside work, OW). Two groups of postal workers were constituted according to the geographical profile of their distribution courses: flat profile (FP; n = 7) vs hilly profile (HP; n = 7). Heart rate (HR) was recorded and energy expenditure (EE) was estimated during both IW and OW. EE was, on average, 1795 +/- 497 Kcal per workday. HR was higher (p < 0.001) during OW (104 +/- 14 bpm) than during IW (80 +/- 7 bpm). HR was highest during the cycling part (109 +/- 13 bpm). Average HR was greater (p < 0.001) for HP (112 +/- 9 bpm) than for FP route (95 +/- 8 bpm). On average, the workload of postmen could be considered as moderate. Nevertheless, the physiological demand greatly increased during the cycling part of OW, especially with hilly geographical profile. The greater physiological strains during the cycling should be factored into the improvement of work organization and delivery materials (e.g. bicycle) for postal workers.

Neuromuscular fatigue following constant versus variable-intensity endurance cycling in triathletes.

The aim of this study was to determine whether or not variable power cycling produced greater neuromuscular fatigue of knee extensor muscles than constant power cycling at the same mean power output. Eight male triathletes (age: 33+/-5 years, mass: 74+/-4 kg, VO2max: 62+/-5 mL kg(-1) min(-1), maximal aerobic power: 392+/-17 W) performed two 30 min trials on a cycle ergometer in a random order. Cycling exercise was performed either at a constant power output (CP) corresponding to 75% of the maximal aerobic power (MAP) or a variable power output (VP) with alternating +/-15%, +/-5%, and +/-10% of 75% MAP approximately every 5 min. Maximal voluntary contraction (MVC) torque, maximal voluntary activation level and excitation-contraction coupling process of knee extensor muscles were evaluated before and immediately after the exercise using the technique of electrically evoked contractions (single and paired stimulations). Oxygen uptake, ventilation and heart rate were also measured at regular intervals during the exercise. Averaged metabolic variables were not significantly different between the two conditions. Similarly, reductions in MVC torque (approximately -11%, P<0.05) after cycling were not different (P>0.05) between CP and VP trials. The magnitude of central and peripheral fatigue was also similar at the end of the two cycling exercises. It is concluded that, following 30 min of endurance cycling, semi-elite triathletes experienced no additional neuromuscular fatigue by varying power (from +/-5% to 15%) compared with a protocol that involved a constant power.

Cycling exercise and the determination of electromechanical delay.

The main aim of the present paper was to address the validity of a methodology proposed in a previous paper [Li L, Baum BS. Electromechanical delay estimated by using electromyography during cycling at different pedaling frequencies. J Electromyogr Kinesiol 2004;14(6):647-52], aimed at determining the electromechanical delay from pedaling exercise performed at various cadences. Twelve trained subjects undertook pedaling bouts corresponding to combinations of cadences ranging from 50 to 100 RPM and power output from 37.5% to 75% of Pmax. As cadence increased, peak torque angle was found to shift forward in crank cycle (from 60-65 degrees at 50 RPM to 75-80 degrees at 100 RPM, depending on the power output level), while muscle bursts shifted backward in accordance with previous works. It is therefore suggested to take into account this peak torque angle lag to improve the methodology proposed by Li and Baum. The present results also evidenced that the central strategy, consisting in earlier muscle activation in crank cycle as cadence increases, is only partial. Neural strategy seems to be a trade-off between mechanical efficiency of muscular force output and coactivation.

Relation between preferred and optimal cadences during two hours of cycling in triathletes.

OBJECTIVES: To determine whether the integrated electromyographic signal of two lower limb muscles indicates preferred cadence during a two hour cycling task. METHODS: Eight male triathletes performed right isometric maximum voluntary contraction (MVC) knee extension and plantar flexion before (P1) and after (P2) a two hour laboratory cycle at 65% of maximal aerobic power. Freely chosen cadence (FCC) was also determined, also at 65% of maximal aerobic power, from five randomised three minute sessions at 50, 65, 80, 95, and 110 rpm. The integrated electromyographic signal of the vastus lateralis and gastrocnemius lateralis muscles was recorded during MVC and the cycle task. RESULTS: The FCC decreased significantly (p<0.01) from P1 (87.4 rpm) to P2 (68.6 rpm), towards the energetically optimal cadence. The latter did not vary significantly during the cycle task. MVC of the vastus lateralis and gastrocnemius lateralis decreased significantly (p<0.01) between P1 and P2 (by 13.5% and 9.6% respectively). The results indicate that muscle activation at constant power was not minimised at specific cadences. Only the gastrocnemius lateralis muscle was affected by a two hour cycling task (especially at 95 and 110 rpm), whereas vastus lateralis remained stable. CONCLUSION: The decrease in FCC observed at the end of the cycle task may be due to changes in the muscle fibre recruitment pattern with increasing exercise duration and cadence.

Neuromuscular function during prolonged pedalling exercise at different cadences.

AIM: The purpose of the present work was to assess the strategies set by the central nervous system in order to provide the power output required throughout a prolonged (1-h) pedalling exercise performed at different cadences (50 rpm, 110 rpm and the freely chosen cadence). METHODS: Neuromuscular (NM) activity of vastus lateralis, rectus femoris, biceps femoris and gastrocnemius lateralis muscles was studied quantitatively [root-mean square (RMS) and mean power frequency (MPF)] and qualitatively (timing of onset and offset of muscle bursts during crank cycle). RESULTS: The present results showed that increased cadence resulted in earlier muscle activation in crank cycle. The influence of cadence on RMS and MPF depended on the considered muscle and its functional role during pedalling. Timing of onset and offset of muscle bursts was not altered by fatigue throughout the prolonged exercise. In contrast, RMS and MPF of some muscles was found to increase during prolonged exercise. CONCLUSION: In summary, the present study revealed that tonic aspects of the NM activity (RMS, MPF) are altered during prolonged pedalling exercise, while phasic aspects are remained unchanged. These results suggest that the strategies set by the central nervous system in order to provide the power output required by the exercise are held constant throughout the exercise, but that quantitative aspects of the central drive are increased in order to adapt to the progressive occurrence of the NM fatigue.