Axel Knicker

Interactive processes link the multiple symptoms of fatigue in sport competition

Muscle physiologists often describe fatigue simply as a decline of muscle force and infer this causes an athlete to slow down. In contrast, exercise scientists describe fatigue during sport competition more holistically as an exercise-induced impairment of performance. The aim of this review is to reconcile the different views by evaluating the many performance symptoms/measures and mechanisms of fatigue. We describe how fatigue is assessed with muscle, exercise or competition performance measures. Muscle performance (single muscle test measures) declines due to peripheral fatigue (reduced muscle cell force) and/or central fatigue (reduced motor drive from the CNS). Peak muscle force seldom falls by <30% during sport but is often exacerbated during electrical stimulation and laboratory exercise tasks. Exercise performance (whole-body exercise test measures) reveals impaired physical/technical abilities and subjective fatigue sensations. Exercise intensity is initially sustained by recruitment of new motor units and help from synergistic muscles before it declines. Technique/motor skill execution deviates as exercise proceeds to maintain outcomes before they deteriorate, e.g. reduced accuracy or velocity. The sensation of fatigue incorporates an elevated rating of perceived exertion (RPE) during submaximal tasks, due to a combination of peripheral and higher CNS inputs. Competition performance (sport symptoms) is affected more by decision-making and psychological aspects, since there are opponents and a greater importance on the result. Laboratory based decision making is generally faster or unimpaired. Motivation, self-efficacy and anxiety can change during exercise to modify RPE and, hence, alter physical performance. Symptoms of fatigue during racing, team-game or racquet sports are largely anecdotal, but sometimes assessed with time-motion analysis. Fatigue during brief all-out racing is described biomechanically as a decline of peak velocity, along with altered kinematic components. Longer sport events involve pacing strategies, central and peripheral fatigue contributions and elevated RPE. During match play, the work rate can decline late in a match (or tournament) and/or transiently after intense exercise bursts. Repeated sprint ability, agility and leg strength become slightly impaired. Technique outcomes, such as velocity and accuracy for throwing, passing, hitting and kicking, can deteriorate. Physical and subjective changes are both less severe in real rather than simulated sport activities. Little objective evidence exists to support exercise-induced mental lapses during sport.A model depicting mind-body interactions during sport competition shows that the RPE centre-motor cortex-working muscle sequence drives overall performance levels and, hence, fatigue symptoms. The sporting outputs from this sequence can be modulated by interactions with muscle afferent and circulatory feedback, psychological and decision-making inputs. Importantly, compensatory processes exist at many levels to protect against performance decrements. Small changes of putative fatigue factors can also be protective.We show that individual fatigue factors including diminished carbohydrate availability, elevated serotonin, hypoxia, acidosis, hyperkalaemia, hyperthermia, dehydration and reactive oxygen species, each contribute to several fatigue symptoms. Thus, multiple symptoms of fatigue can occur simultaneously and the underlying mechanisms overlap and interact. Based on this understanding, we reinforce the proposal that fatigue is best described globally as an exercise-induced decline of performance as this is inclusive of all viewpoints.

Energy Cost and Pole Forces during Nordic Walking under Different Surface Conditions

INTRODUCTION The purpose of the study was to identify the effect of three different surfaces on energy consumption and the forces acting on the walking poles during ground contact in Nordic walking (NW). METHODS Thirteen female NW instructors (age = 26 +/- 4 yr, weight = 58.5 +/- 4.2 kg, height = 168.1 +/- 4.6 cm) volunteered in the study. The subjects walked a distance of 1200 m at a controlled, constant speed of 2.2 m x s(-1) on each of a concrete surface (C), an artificial athletics track (A), and a naturally grown soccer lawn (G). They used NW poles with inbuilt strain gauge force transducers to measure ground reaction forces acting along the long axes of the poles. Oxygen uptake, capillary blood lactate (La), HR, and RPE were measured before and after the tests. RESULTS Impact forces, maximum forces, force rates during ground contact identified from the registered force time histories, displayed significant differences related to the surface conditions. However, force time integrals did not show surface-related differences. Relative oxygen consumption showed significant differences between NW on C and on G whereas no surface-related differences could be identified between the surface conditions for the parameters La, HR, and RPE. CONCLUSION Our data indicate that the impulse that is generated by the poles on the subjects is identical between the varying surfaces. Because there are differences for the oxygen uptake between C and G, the main regulator for the propulsion must be the musculature of the lower extremities. The work of the upper extremities seems to be a luxury effort for Nordic walkers with a proper technique.

12-Week Resistance Training with Breast Cancer Patients during Chemotherapy: Effects on Cognitive Abilities

(CG). Patients in the IG participated in a 60-min session of resistance training twice a week for 12 weeks, performing 3 sets of 8–12 repetitions of 10 different exercises at 55–75% of their hypothetical 1-repetition maximum. Exercise sessions were supervised and performed at a healthorientated fitness studio. Cognitive functions were assessed by 4 neuropsychological tests. The MEMO memory test [6] was applied to test verbal memory, the Wilde intelligence subtest (WIT) [7] to determine the working memory, and the d2 test of attention, consisting of 2 different tests, to provide information about focused attention and concentration abilities [8]. Assessments were conducted at the beginning (pre) and at the end (post) of the 12-week physical intervention in the IG, whereas the CG was only tested at the end of the trial. The pre-test was conducted during chemotherapy and the post-test 1–2 weeks after its termination. Statistical analyses consisted of a paired/dependent t-test (type 1) to assess intergroup changes in the IG and an independent t-test (type 2, 2 samples, same variance) to identify differences between the IG and the CG at the end of the trial.

Factors influencing the reproducibility of isokinetic knee flexion and extension test findings

BACKGROUND:Although the reliabilityof isokinetic strength tests of kneeflexors (flex) and extensors (ext) has been examined several times, statistical evidence about the influence of internal and external factors is missing. OBJECTIVE: This study aims to examine the impact of familiarisation, muscle group, contraction mode, angular velocity and test parameters on the reproducibility of findings derived from an isokinetic dynamometer (IsoMed 2000). METHODS: Thirty-three male subjects (mean age: 22.3 years) with no prior experience of isokinetic exercise participated in three identical test sessions (T1, T2, T3), each separated by 48–72 h. Peak moment (PM), angle of peak moment (APM) and contractional work (CW) were determined unilaterally (left and right) during maximum concentric (con) and eccentric (ecc) knee flexion (abdominal position) and extension (supine position) at 30, 90 and 150 ◦ /s, respectively. An ANOVA with repeated measures confirmed systematic bias. Reproducibility of consecutive tests (T1–T2, T2–T3) was assessed by calculating the intra-class correlation coefficient (ICC 2,1) (relative reliability) as well as the standard error of measurement (SEM) (absolute reliability). ICC values were averaged according to respective factors (Fisher’s z-transformation) and tested for significant differences by Steiger’s formulas. RESULTS:PMand CW demonstrated ahigh absolute reliability(SEM:4.7–10.5%). Relativereproducibility varied considerably (p 0.05) between muscles (ecc flex > ecc ext), contraction modes (con ext > ecc ext) and test parameters (PM = CW > APM), but did not depend on angular velocity (30 = 90 = 150 ◦ /s). Due to familiarisation the reliability of PM obtained from eccentric knee extensions significantly increased (T2–T3 > T1–T2). CONCLUSIONS: These results improve the development and execution of reliable isokinetic strength testing protocols for unilateral knee flexion and extension together with the interpretation of different test parameters.

Velocity‐specific and time‐dependent adaptations following a standardized Nordic Hamstring Exercise training

The Nordic Hamstring Exercise (NHE) is effective for selective hamstring strengthening to improve muscle balance between knee flexors and extensors. The purpose of this study (within subject design of repeated measures) was to determine the effects of a standardized 4‐week NHE training on thigh strength and muscle balance with concomitant kinetic and kinematic monitoring. Sixteen male sprinters (22 years, 181 cm, 76 kg) performed a standardized 4‐week NHE training consisting of three sessions per week (each 3×3 repetitions). Six rope‐assisted and six unassisted sessions were performed targeting at a constant knee extension angular velocity of ~15°/s across a ~90‐100° knee joint range of motion. Kinetic (peak and mean moment, impulse) and kinematic parameters (eg, ROM to downward acceleration, ROMDWA) were recorded during selected sessions. Unilateral isokinetic tests of concentric and eccentric knee flexors and extensors quantified muscle group‐, contraction mode‐, and velocity‐specific training adaptations. Peak moments and contractional work demonstrated strong interactions of time with muscle group, contraction modes, and angular velocities (η²>.150). NHE training increased eccentric hamstring strength by 6%‐14% as well as thigh muscle balance with biggest adaptations at 150°/s 2 weeks after NHE training. Throughout the training period significant increases (P<.001) of peak (η²=.828) and mean moments (η²=.611) became apparent, whereas the impulse and the ROMDWA of unassisted NHE repetitions remained unchanged (P>.05). A 4‐week NHE training significantly strengthened the hamstrings and improved muscle balance between knee flexors and extensors. Despite the slow training velocity, biggest adaptations emerged at the highest velocity 2 weeks after training ended.

The dynamic control ratio at the equilibrium point (DCRe): introducing relative and absolute reliability scores.

ABSTRACT Analytical methods to assess thigh muscle balance need to provide reliable data to allow meaningful interpretation. However, reproducibility of the dynamic control ratio at the equilibrium point has not been evaluated yet. Therefore, the aim of this study was to compare relative and absolute reliability indices of its angle and moment values with conventional and functional hamstring–quadriceps ratios. Furthermore, effects of familiarisation and angular velocity on reproducibility were analysed. A number of 33 male volunteers participated in 3 identical test sessions. Peak moments (PMs) were determined unilaterally during maximum concentric and eccentric knee flexion (prone) and extension (supine position) at 0.53, 1.57 and 2.62 rad · s–1. A repeated measure, ANOVA, confirmed systematic bias. Intra-class correlation coefficients and standard errors of measurement indicated relative and absolute reliability. Correlation coefficients were averaged over respective factors and tested for significant differences. All balance scores showed comparable low-to-moderate relative (<0.8–0.9) and good absolute reliability (<10%). Relative reproducibility of dynamic control equilibrium parameters augmented with increasing angular velocity, but not with familiarisation. At 2.62 rad · s–1, high (moment: 0.906) to moderate (angle: 0.833) relative reliability scores with accordingly high absolute indices (4.9% and 6.4%) became apparent. Thus, the dynamic control equilibrium is an equivalent method for the reliable assessment of thigh muscle balance.

Brain-imaging during an isometric leg extension task at graded intensities

Imaging the brain during complex and intensive movements is challenging due to the susceptibility of brain-imaging methods for motion and myogenic artifacts. A few studies measured brain activity during either single-joint or low-intensity exercises; however, the cortical activation state during larger movements with increases up to maximal intensity has barely been investigated so far. Eleven right-handed volunteers (22–45 years in age) performed isometric leg extensions with their right leg at 20, 40, 60, 80, and 100% of their maximal voluntary contraction. Contractions were hold for 20 s respectively. Electroencephalographic (EEG) and electromyographic (EMG) activity was recorded. Standardized low-resolution brain electromagnetic tomography (sLORETA) was used to localize the cortical current density within the premotor (PMC), primary motor (M1), primary somatosensory (S1) and somatosensory association cortex (SAC). ANOVA was used for repeated measures for comparison of intensities and between the left and right hemispheres. The quality of the EEG signal was satisfying up to 80% intensity. At 100% half of the participants were not able to keep their neck and face muscles relaxed, leading to myogenic artifacts. Higher contralateral vs. ipsilateral hemispheric activity was found for the S1, SAC and, PMC. M1 possessed higher ipsilateral activity. The highest activity was localized in the M1, followed by S1, PMC, and SAC. EMG activity and cortical current density within the M1 increased with exercise intensity. EEG recordings during bigger movements up to submaximal intensity (80%) are possible, but maximal intensities are still hard to investigate when subjects contracted their neck and face muscles at the same time. Isometric contractions mainly involve the M1, whereas the S1, PMC, and SAC seem not to be involved in the force output. Limitations and recommendations for future studies are discussed.

Response to the Letter to the Editor of Sorci et al. ''Causes of elevated serum levels of S100B protein in athletes''

We view the interest generated by our paper positively and appreciate the views of Drs. Sorci, Riuzzi and Donato. In their response to our paper (Schulte et al. 2012), Sorci et al. pose three important considerations regarding the contribution of peripheral sources to increased peripheral S100B levels and the function of S100B itself. In the following we address Sorci et al. main points in this response. First, we concur with this suggestion—a point we acknowledge in our article—that S100B is also expressed in soft tissue outside the brain and possibly released by damaged skeletal muscle tissue due to vigorous physical activity. Secondly, findings regarding the connection between lipolysis/fat tissue and S100B are equivocal. That said, we would agree with Sorci et al. as it would be premature to exclude the possibility that increased lipolysis by physical activity might be a potential mechanism in increasing peripheral S100B concentration. Finally, Sorci et al. indicate the functions of S100B regarding tissue repair/regeneration or amplification of the local inflammatory response. Based on the fact that S100B has opposing effects depending on its concentration (neurotoxic and neuroprotective effects), we wholeheartedly embrace the conclusion that S100B may not only be a biomarker of pathological conditions such as concussion/mild traumatic brain injury, but also a potential indicator of neuroprotective processes. Independent of whether S100B has neurotoxic or neuroprotective effects, it is the most widely investigated biomarker in the assessment of traumatic brain injury. A peripheral concentration of S100B in serum less than the recommended cut-off level of 0.1 lg/L has been linked to negative computer tomography (CT) scans regarding TBI with a sensitivity of 96.8 % and a specificity of 42.5 % (Pandor et al. 2011). Early identification of sports-related brain injury, like concussion, is essential in preventing athletes’ poor clinical outcomes and optimizing post-injury performance. The identification of concussed athletes based on S100B assessment requires accurate reference values. Increased peripheral S100B levels C0.1 lg/L do not necessarily imply that an athlete is concussed. Due to the fact that there are multiple factors that potentially influence S100B serum concentration levels (e.g. myocytic damage and lipolysis), S100B levels might exceed the cutoff value of 0.1 lg/L without the contribution of cerebral sources and thus cannot be attributed to concussion. In addition to the influencing factors mentioned by Sorci et al., we want to point out that factors such as sex, age and color of skin (melanocytical activity) may also influence basic peripheral S100B concentrations (Gazzolo et al. 2003). Hence, it is important to establish individual matched reference values of S100B for concussed athletes regarding demographic factors such as sex, age, race, and other salient factors associated with physical activity (e.g. Communicated by Hakan Westerblad.

Gas exchange kinetics following concentric-eccentric isokinetic arm and leg exercise

PURPOSE To evaluate the effects of exercise velocity (60, 150, 240deg∙s-1) and muscle mass (arm vs leg) on changes in gas exchange and arterio-venous oxygen content difference (avDO2) following high-intensity concentric-eccentric isokinetic exercise. METHODS Fourteen subjects (26.9±3.1years) performed a 3×20-repetition isokinetic exercise protocol. Recovery beat-to-beat cardiac output (CO) and breath-by-breath gas exchange were recorded to determine post-exercise half-time (t1/2) for oxygen uptake (V˙O2pulm), carbon dioxide output (V˙CO2pulm), and ventilation (V˙E). RESULTS Significant differences of the t1/2 values were identified between 60 and 150deg∙s-1. Significant differences in the t1/2 values were observed between V˙O2pulm and V˙CO2pulm and between V˙CO2pulm and V˙E. The time to attain the first avDO2-peak showed significant differences between arm and leg exercise. CONCLUSIONS The present study illustrates, that V˙O2pulm kinetics are distorted due to non-linear CO dynamics. Therefore, it has to be taken into account, that V˙O2pulm may not be a valuable surrogate for muscular oxygen uptake kinetics in the recovery phases.