Daniel Theisen - Academia.edu (original) (raw)

Papers by Daniel Theisen

The International Journal of Cardiovascular Imaging, 2014

The purpose of the study is feasibility of dynamic CT perfusion imaging to detect and differentia... more The purpose of the study is feasibility of dynamic CT perfusion imaging to detect and differentiate ischemic and infarcted myocardium in a large porcine model. 12 Country pigs completed either implantation of a 75 % luminal coronary stenosis in the left anterior descending coronary artery simulating ischemia or balloon-occlusion inducing infarction. Dynamic CT-perfusion imaging (100 kV, 300 mAs), fluorescent microspheres, and histopathology were performed in all models. CT based myocardial blood flow (MBFCT), blood volume (MBVCT) and transit constant (Ktrans), as well as microsphere&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s based myocardial blood flow (MBFMic) were derived for each myocardial segment. According to histopathology or microsphere measurements, 20 myocardial segments were classified as infarcted and 23 were ischemic (12 and 14 %, respectively). Across all perfusion states, MBFCT strongly predicted MBFMic (β 0.88 ± 0.12, p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). MBFCT, MBVCT, and Ktrans were significantly lower in ischemic/infarcted when compared to reference myocardium (all p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.01). Relative differences of all CT parameters between affected and non-affected myocardium were higher for infarcted when compared to ischemic segments under rest (48.4 vs. 22.6 % and 46.1 vs. 22.9 % for MBFCT, MBVCT, respectively). Under stress, MBFCT was significantly lower in infarcted than in ischemic myocardium (67.8 ± 26 vs. 88.2 ± 22 ml/100 ml/min, p = 0.002). In a large animal model, CT-derived parameters of myocardial perfusion may enable detection and differentiation of ischemic and infarcted myocardium.

British Journal of Sports Medicine, 2014

The American journal of sports medicine, Jan 4, 2015

Excessive physiological anterior and rotational knee laxity is thought to be a risk factor for no... more Excessive physiological anterior and rotational knee laxity is thought to be a risk factor for noncontact anterior cruciate ligament (ACL) injuries and inferior reconstruction outcomes, but no thresholds have been established to identify patients with increased laxity. (1) To determine if the healthy contralateral knees of ACL-injured patients have greater anterior and rotational knee laxity, leading to different laxity profiles (combination of laxities), compared with healthy control knees and (2) to set a threshold to help discriminate anterior and rotational knee laxity between these groups. Case-sectional study; Level of evidence, 3. A total of 171 healthy contralateral knees of noncontact ACL-injured patients (ACL-H group) and 104 healthy knees of control participants (CTL group) were tested for anterior and rotational laxity. Laxity scores (measurements corrected for sex and body mass) were used to classify knees as hypolax (score <-1), normolax (between -1 and 1), or hyper...

The purpose of this study was to analyse lower leg skin blood è ow (laser Doppler è owmetry) in é... more The purpose of this study was to analyse lower leg skin blood è ow (laser Doppler è owmetry) in é ve individuals with high- level paraplegia (T5- T9), six participants with low-level paraplegia (T10- T12) and six able-bodied controls during 3-minute light and heavy arm-cranking exercises ( π15% and 80% peakpower output, respectively). Throughout light exercise, cutaneous vasoconstriction was shown

Medical Radiology, 2009

... collateral branches (eg lumbar arteries) Type III: midgraft leak, with blood flow through 3. ... more ... collateral branches (eg lumbar arteries) Type III: midgraft leak, with blood flow through 3. the graft due to inadequate or ineffective sealing of overlapping joints or rupture of the graft fabric Type IV ... This can lead to graft thrombosis, endoleaks or aneurysm rupture (FillinGer 1999). ...

International journal of sports medicine, 2001

This study investigated whether a 60-minute arm-cranking exercise at 50% of the individual maxima... more This study investigated whether a 60-minute arm-cranking exercise at 50% of the individual maximal power output would increase lower limb skin blood flow (laser Doppler flowmetry) in individuals with high-level (T5-T9; n = 6) and low-level paraplegia (T10-T12; n = 6), compared to 6 able-bodied controls. Significant (P < 0.05) group by time interactions (two-way repeated measures ANOVA) were found for leg cutaneous vascular conductance, leg skin temperature and esophageal temperature. Cutaneous vascular conductance increased to a peak of approximately 180% of pre-exercise rest in both paraplegic groups and to -436% in the control group, with differences after 15, 30, 45 and 60 minutes of exercise. Leg skin temperature increased by approximately 0.3 C in individuals with paraplegia and decreased by approximately 2.0 C in able-bodied. Esophageal temperature increases at the end of exercise were higher in individuals with paraplegia (approximately 0.9 C) than in able-bodied subjects ...

International journal of sports medicine, 1999

Forty-six male wheelchair basketball players performed a set of field tests to evaluate aerobic c... more Forty-six male wheelchair basketball players performed a set of field tests to evaluate aerobic capacity (25 m shuttle run), anaerobic capacity (30s sprint), and six specific wheelchair basketball skills. Overall test-retest reliability (n = 20) ranged from r = 0.65 to r = 0.97. To study the validity (criterion related evidence) of the shuttle run test, heart rate (HR) was recorded for 15 subjects, who also performed a continuous, multistage arm cranking exercise until volitional fatigue. Moderate to high correlations were calculated between shuttle run distances covered (1375 243,6 m) and VO2max (2208+/-461.6 mL/min) and POmax (93.8+/-17.97 W), measured during maximal arm cranking (respectively r = 0.64 and r = 0.87). Maximal HR during shuttle run (174.9+/-16.6 B/min) and arm cranking (169+/-14.21 B/min) were correlated (r = 0.78). High correlations between shuttle run test and anaerobic field tests, however, indicate high implication of anaerobic and wheelchair maneuverability per...

Scandinavian Journal of Medicine & Science in Sports, 2014

Running-related injuries remain problematic among recreational runners. We evaluated the associat... more Running-related injuries remain problematic among recreational runners. We evaluated the association between having sustained a recent running-related injury and speed, and the strike index (a measure of footstrike pattern, SI) and spatiotemporal parameters of running. Forty-four previously injured and 46 previously uninjured runners underwent treadmill running at 80%, 90%, 100%, 110%, and 120% of their preferred running speed. Participants wore a pressure insole device to measure SI, temporal parameters, and stride length (Slength ) and stride frequency (Sfrequency ) over 2-min intervals. Coefficient of variation and detrended fluctuation analysis provided information on stride-to-stride variability and correlative patterns. Linear mixed models were used to compare differences between groups and changes with speed. Previously injured runners displayed significantly higher stride-to-stride correlations of SI than controls (P = 0.046). As speed increased, SI, contact time (Tcontact ), stride time (Tstride ), and duty factor (DF) decreased (P < 0.001), whereas flight time (Tflight ), Slength , and Sfrequency increased (P < 0.001). Stride-to-stride variability decreased significantly for SI, Tcontact , Tflight , and DF (P ≤ 0.005), as did correlative patterns for Tcontact , Tstride , DF, Slength , and Sfrequency (P ≤ 0.044). Previous running-related injury was associated with less stride-to-stride randomness of footstrike pattern. Overall, runners became more pronounced rearfoot strikers as running speed increased.

European Journal of Applied Physiology, 2000

The veno-arteriolar reflex (VAR) in spinal-cord-injured subjects (SCI) has been attributed little... more The veno-arteriolar reflex (VAR) in spinal-cord-injured subjects (SCI) has been attributed little interest, although it might contribute substantially to their blood redistribution. This peripheral reflex response, which is based on an axon reflex, consists of a reduction in limb blood flow following an increase in venal transmural pressure. The purpose of the present investigation was to assess the peripheral and

Objectives: To investigate the association between training-related characteristics and running-r... more Objectives: To investigate the association between training-related characteristics and running-related injury using a new conceptual model for running-related injury generation, focusing on the synergy between training load and previous injuries, short-term running experience or body mass index (> or <25 kg m −2 ). Design: Prospective cohort study with a 9-month follow-up. Methods: The data of two previous studies using the same methodology were revisited. Recreational runners (n = 517) reported information about running training characteristics (weekly distance, frequency, speed), other sport participation and injuries on a dedicated internet platform. Weekly volume (dichotomized into <2 h and ≥2 h) and session frequency (dichotomized into <2 and ≥2) were the main exposures because they were considered necessary causes for running-related injury. Non-trainingrelated characteristics were included in Cox regression analyses as effect-measure modifiers. Hazard ratio was the measure of association. The size of effect-measure modification was calculated as the relative excess risk due to interaction. Results: One hundred sixty-seven runners reported a running-related injury. Crude analyses revealed that weekly volume <2 h (hazard ratio = 3.29; 95% confidence intervals = 2.27; 4.79) and weekly session frequency <2 (hazard ratio = 2.41; 95% confidence intervals = 1.71; 3.42) were associated with increased injury rate. Previous injury was identified as an effect-measure modifier on weekly volume (relative excess risk due to interaction = 4.69; 95% confidence intervals = 1.42; 7.95; p = 0.005) and session frequency (relative excess risk due to interaction = 2.44; 95% confidence intervals = 0.48; 4.39; p = 0.015). A negative synergy was found between body mass index and weekly volume (relative excess risk due to interaction = −2.88; 95% confidence intervals = −5.10; −0.66; p = 0.018). Conclusions: The effect of a runner's training load on running-related injury is influenced by body mass index and previous injury. These results show the importance to distinguish between confounding and effect-measure modification in running-related injury research. (L. Malisoux). to elucidate the mechanisms involved in RRI generation, 6,7 a prerequisite for successful injury prevention measures. To date, evidence on RRI aetiology is virtually non-existent. One of the main reasons regularly highlighted is the absence of largescale prospective cohort studies. In addition, the conceptual and statistical approach used for data-analysis has been given insufficient attention. The classical way used by many authors is to run regression analyses, where all variables thought to be related to injury are first tested separately for their association with RRI. Next, those below a certain p-value are included in a final adjusted model. This approach implies that each included variable is a confounder for the outcome and is directly associated with it.

European Journal of Radiology, 2014

To find out whether the use of accelerated 2D-selective parallel-transmit excitation MRI for diff... more To find out whether the use of accelerated 2D-selective parallel-transmit excitation MRI for diffusion-weighted EPI (pTX-EPI) offers advantages over conventional single-shot EPI (c-EPI) with respect to different aspects of image quality in the MRI of the pancreas. The MRI examinations of 33 consecutive patients were evaluated in this prospective and IRB-approved study. PTX-EPI was performed with a reduced (zoomed) FOV of 230 × 118 mm(2). The 2D-RF pulse of pTX-EPI was accelerated, i.e. shortened by a factor of 1.7 (pTX-acceleration factor). C-EPI used a full-FOV of 380 × 285 mm(2). In a qualitative analysis, two experienced readers evaluated 3 different aspects of image quality on 3- to 5-point Likert scales. Additionally, apparent diffusion coefficients (ADCs) were determined in both c-EPI and pTX-EPI in normal-appearing pancreatic tissue using regions of interests (ROIs). Mean ADC values and standard deviations were compared between the two techniques. The reduced-FOV pTX-EPI was superior to c-EPI with respect to overall image quality (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.0001) and identifiability of the pancreatic ducts (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01). Artifacts were significantly less severe in pTX-EPI (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01). The mean ADC values of c-EPI (1.29 ± 0.19 × 10(-3)mm(2)/s) and pTX-EPI (1.27 ± 0.17 × 10(-3)mm(2)/s) did not differ significantly between the two techniques (p=0.44). The variation within the ROIs as measured by the standard deviation was significantly lower in pTX-EPI (0.095 × 10(-3)mm(2)/s) than in c-EPI (0.135 × 10(-3)mm(2)/s), p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05. PTX-accelerated EPI with spatially-selective excitation and reduced FOV leads to substantial improvements in DWI of the pancreas with respect to different aspects of image quality without significantly influencing the ADC values.

Technology in Cancer Research and Treatment, 2014

The purpose of this study was to evaluate the role of diffusion-weighted MR imaging (DW-MRI) in t... more The purpose of this study was to evaluate the role of diffusion-weighted MR imaging (DW-MRI) in the assessment of treatment response of primary or secondary liver malignancies after stereotactic radiosurgery (SRS) using robotic radiosurgery. All patients who underwent SRS therapy for hepatic malignancies who had pre- and post-interventional MR examinations including DW-MRI at our hospital between 02/2010 and 02/2012 were included. A retrospective analysis of the institutional imaging database identified 13 patients (4 men, 9 women, mean age: 66 years) with a total of 14 primary or secondary liver malignancies. Criteria of tumor response to treatment were a decrease in size and/or loss of contrast enhancement as assessed with respect to RECIST criteria. Mean apparent diffusion coefficient (ADC) values for normal liver parenchyma and hepatic masses in each MR examination were calculated and compared using two-tailed, paired t-test with a significance level of 0.05. Mean ADC values of liver malignancies were 1.10 ± 0.30 x 10(-3) mm(2)/s, 1.48 ± 0.35 x 10(-3) mm(2)/s and 1.56 ± 0.40 x 10(-3) mm(2)/s on pre-interventional, the first post-interventional, and the second post-interventional DW-MRI. There was a significant increase of ADC values between the pre-interventional examination and the first and second post-interventional follow-up exams (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01 and p = 0.01, respectively). However, there was no statistical difference between the ADC values of the first and second post-interventional MRI. ADC values of normal liver parenchyma did not show significant changes in ADC values during pre- and post-interventional MRI. ADC measurements may allow the evaluation of response to treatment of hepatic malignancies by SRS. ADC values of liver malignancies increase significantly after SRS treatment.

Scandinavian Journal of Medicine & Science in Sports, 2013

The aim of this study was to determine if runners who use concomitantly different pairs of runnin... more The aim of this study was to determine if runners who use concomitantly different pairs of running shoes are at a lower risk of running-related injury (RRI). Recreational runners (n = 264) participated in this 22-week prospective follow-up and reported all information about their running session characteristics, other sport participation and injuries on a dedicated Internet platform. A RRI was defined as a physical pain or complaint located at the lower limbs or lower back region, sustained during or as a result of running practice and impeding planned running activity for at least 1 day. One-third of the participants (n = 87) experienced at least one RRI during the observation period. The adjusted Cox regression analysis revealed that the parallel use of more than one pair of running shoes was a protective factor [hazard ratio (HR) = 0.614; 95% confidence interval (CI) = 0.389-0.969], while previous injury was a risk factor (HR = 1.722; 95%CI = 1.114-2.661). Additionally, increased mean session distance (km; HR = 0.795; 95%CI = 0.725-0.872) and increased weekly volume of other sports (h/week; HR = 0.848; 95% CI = 0.732-0.982) were associated with lower RRI risk. Multiple shoe use and participation in other sports are strategies potentially leading to a variation of the load applied to the musculoskeletal system. They could be advised to recreational runners to prevent RRI.

PLoS ONE, 2012

A common nonsense polymorphism in the ACTN3 gene results in the absence of α-actinin-3 in XX indi... more A common nonsense polymorphism in the ACTN3 gene results in the absence of α-actinin-3 in XX individuals. The wild type allele has been associated with power athlete status and an increased force output in numeral studies, though the mechanisms by which these effects occur are unclear. Recent findings in the Actn3(-/-) (KO) mouse suggest a shift towards &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;slow&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; metabolic and contractile characteristics of fast muscle fibers lacking α-actinin-3. Skinned single fibers from the quadriceps muscle of three men with spinal cord injury (SCI) were tested regarding peak force, unloaded shortening velocity, force-velocity relationship, passive tension and calcium sensitivity. The SCI condition induces an &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;equal environment condition&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; what makes these subjects ideal to study the role of α-actinin-3 on fiber type expression and single muscle fiber contractile properties. Genotyping for ACTN3 revealed that the three subjects were XX, RX and RR carriers, respectively. The XX carrier&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s biopsy was the only one that presented type I fibers with a complete lack of type II(x) fibers. Properties of hybrid type II(a)/II(x) fibers were compared between the three subjects. Absence of α-actinin-3 resulted in less stiff type II(a)/II(x) fibers. The heterozygote (RX) exhibited the highest fiber diameter (0.121±0.005 mm) and CSA (0.012±0.001 mm(2)) and, as a consequence, the highest peak force (2.11±0.14 mN). Normalized peak force was similar in all three subjects (P = 0.75). Unloaded shortening velocity was highest in R-allele carriers (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001). No difference was found in calcium sensitivity. The preservation of type I fibers and the absence of type II(x) fibers in the XX individual indicate a restricted transformation of the muscle fiber composition to type II fibers in response to long-term muscle disuse. Lack of α-actinin-3 may decrease unloaded shortening velocity and increase fiber elasticity.

PLoS ONE, 2014

Purpose: The aim of this study was to assess the diagnostic performance of ECG-gated non-contrast... more Purpose: The aim of this study was to assess the diagnostic performance of ECG-gated non-contrast-enhanced quiescent interval single-shot (QISS) magnetic resonance angiography at a magnetic field strength of 3 Tesla in patients with advanced peripheral arterial occlusive disease (PAOD).

Medicine & Science in Sports & Exercise, 2004

The purpose of this study was to determine gross mechanical efficiency (ME) at different power ou... more The purpose of this study was to determine gross mechanical efficiency (ME) at different power output (PO) levels of synchronous hand cycling and to evaluate the influence of increasing PO by changing crank rate or resistance in wheelchair users with experience in hand cycling. Nine male participants with spinal cord injury randomly performed three maximal incremental hand cycling tests using a computer controlled cycle ergometer. Each test started at a PO level of 50 W with increments of 10 W. In the velocity protocol, PO was increased via crank rate while resistance was constant (VEL). In the resistance protocol PO was increased via resistance while crank rate was constant (RES). In the freely chosen frequency protocol, the participants could freely select their crank rate while resistance was automatically adjusted to obtain the desired PO (FCF). Peak physiological responses were similar in all three tests, whereas PO max was lower in VEL compared with RES and FCF. Similar values for gross ME were found in both RES and FCF protocols, although systematically higher and increasing crank rates were adopted throughout FCF. Nevertheless, differences in gross ME at comparable relative (RES &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; VEL at 60 and 80% of PO range: 14.09 and 14.40% vs 13.02 and 13.11%, respectively) and absolute (RES, FCF &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; VEL at 90 W: 14.47, 14.47, and 13.43%, respectively) PO levels were demonstrated. These results suggest that during synchronous hand cycling the freely chosen crank rate is not necessarily the most economical, that high crank rates result in a lower ME at a given PO and that freely chosen crank rates increase with increasing PO levels.

Medicine & Science in Sports & Exercise, 2007

Many exercise programs designed by trainers have the specific aim to enhance strength, endurance,... more Many exercise programs designed by trainers have the specific aim to enhance strength, endurance, or power of certain muscle groups to improve athletic performance. Muscle training is also an important component of rehabilitation to limit atrophy associated with immobilization, aging, or disease. To optimize exercise interventions, a good understanding of the response to various training programs and the identification of the mechanisms that influence muscle function are required. Changes in the performance of muscle contraction are associated, among other things, with muscle fiberYtype expression and functional properties of the contractile apparatus. Chemically skinned, single fibers is the only model that allows study of the mechanical properties of human muscle fibers as a function of the expression of myosin heavy-chain isoforms. Recently, this model has been used to explore the functional adaptations after different types of solicitations. The current results of the literature indicate that cross-sectional area and force of a specific fiber type are enhanced after resistance training, whereas maximal unloaded shortening velocity is increased by endurance training. Plyometric training improves both fiber force and shortening velocity. Fiber peak power is increased after resistance or plyometric training, and on a long-term basis it is decreased after endurance training. Studies on elderly individuals indicate that this population may react differently with respect to some single-fiber adaptations after training. Generally, training regimens tend to decrease the proportion of type IIx fibers. The available data in the literature make it possible to formulate recommendations applicable to sport science and rehabilitation.

Medicine & Science in Sports & Exercise, 2006

Purpose: To study the effect of plyometric training on Ca 2+ sensitivity and the influence of tro... more Purpose: To study the effect of plyometric training on Ca 2+ sensitivity and the influence of troponin T (TnT) isoforms on Ca 2+ -activation properties in skinned human muscle fibers. Methods: Biopsies were obtained from the vastus lateralis of eight men before and after the training period. Chemically skinned fibers were evaluated regarding their Ca 2+ -activation properties and were classified according to their myosin heavy chain (MHC) contents and analyzed regarding their slow and fast TnT isoforms. Results: After training, significant improvements (P G 0.05) were found for static jump, countermovement jump, 6 Â 5-m shuttle-run test, and leg-press performances. An 8% increase in the proportion of type IIa fibers (P G 0.05) was observed. Single-fiber diameters increased by 11% in type I (P G 0.01), 10% in type IIa (P G 0.001), and 15% in type IIa/IIx fibers (P G 0.001). Peak fiber force increased by 35% in type I (P G 0.001), 25% in type IIa (P G 0.001), and 57% in type IIa/IIx fibers (P G 0.01). The Ca 2+ -activation threshold was not altered by training, but the Ca 2+ concentration required to elicit half-maximal activation showed a decreasing trend, with significant changes in type I fibers (P G 0.001). Cooperativity at low Ca 2+ concentrations was increased in type I and type IIa/IIx fibers (P G 0.05). Type I fibers exclusively expressed slow TnT isoforms, and type II fibers were always associated with fast TnT isoforms, independent of training status. Therefore, changes in Ca 2+ sensitivity after training could not be explained by differential fast or slow TnT isoform expression. Conclusion: Plyometric training increased single-fiber Ca 2+ sensitivity, especially in type I fibers. These changes could not be explained by a modified TnT isoform expression pattern.