Hip and knee implants can either be fixed without cement, press-fit, or with bone cement. Real-world data from arthroplasty registers, as well as studies provide a broad database for the discussion of cemented versus uncemented arthroplasty procedures. What does current evidence from international arthroplasty registries and meta-analyses recommend regarding cemented or cementless fixation of hip and knee implants? A recommendation is generated by means of direct data comparison from the arthroplasty registries of eight countries (USA, Germany, Australia, UK, Sweden, Norway, New Zealand, Netherlands), the comparison of 22 review studies and meta-analyses based on registry data, as well as an evaluation of recommendations of healthcare systems from different nations. For this purpose, reviews and meta-analyses were selected where the results were statistically significant, as were the annual reports of the arthroplasty registries that were current at the time of writing. For knee arthroplasties, long survival time as well as lower risk of revision can be achieved with the support of cemented fixation with antibiotic-loaded bone cement. In patients aged 70 years and older, cemented fixation of hip stem implants significantly reduces risk of intraoperative or postoperative periprosthetic fracture (quadruple). This applies both to elective total hip arthroplasties and to hemiarthroplasty after femoral neck fractures. Antibiotic-loaded bone cement significantly (p = 0.041) reduces the risk of periprosthetic infection, especially in patients with femoral neck fractures. Total knee replacement with antibiotic-loaded bone cement is well established internationally and is evidence-based. Registry data and meta-analyses recommend cemented fixation of the hip stem in older patients. In Germany, USA and Australia these evidence-based recommendations still must be transferred to daily practice.

Background: Hip and knee implants can be either fixated without cement, press-fit, or with bone cement. Real-world data from arthroplasty registers, as well as studies, provide a broad database for the discussion of cemented versus uncemented arthroplasty procedures. Objectives: What is the recommendation for cemented or cementless anchorage of hip and knee implants based on the current evidence from international arthroplasty registries and meta-analyses? Methods: A recommendation is generated by means of a direct comparison of data from the arthroplasty registries of eight different countries (USA, Germany, Australia, UK, Sweden, Norway, New Zealand, and The Netherlands), the comparison of 22 review studies and meta-analyses based on registry data, as well as the evaluation of the recommendation of healthcare systems of different nations. For this purpose, reviews and meta-analyses whose results were statistically significant were selected, as were the annual reports of the arthroplasty registries that were current at the time of writing. Results: For knee endoprostheses, a long survival time, as well as a lower risk of revision can be achieved with the help of cemented anchorage with antibiotic-laden bone cement. In patients aged 70 years and older, cemented anchorage of the hip stem implant significantly reduces the risk of intraoperative or postoperative periprosthetic fracture (times four), this applies both to elective total hip arthroplasties (TEPs) and to hemiarthroplasty after femoral neck fractures. Antibiotic-loaded bone cement significantly (p = 0.041) reduces the risk of periprosthetic infection, especially in patients with femoral neck fractures. Conclusions: Total knee replacement with antibiotic-loaded bone cement is well established in Germany and evidence based. Registry data and meta-analyses recommend cemented fixation of the hip stem in older patients-in Germany the evidence-based recommendations must still be transferred to daily practice.

Zusammenfassung Hintergrund In der Endoprothetik gibt es Hüft- und Knieimplantate, die zementfrei, „press-fit“ oder mit Knochenzement verankert werden. Real-World-Evidenz aus Endoprothesenregistern sowie Studien bieten eine breite Datenbasis zur Diskussion von zementierten im Vergleich zu zementfreien Endoprothesen. Fragestellung Wie lautet die Empfehlung zur zementierten oder zementfreien Verankerung von Hüft- und Knieimplantaten, basierend auf der aktuellen Evidenzlage internationaler Endoprothesenregister und Metaanalysen? Material und Methode Mittels des direkten Vergleichs von Daten aus den Endoprothesenregistern acht verschiedener Länder (USA, Deutschland, Australien, UK, Schweden, Norwegen, Neuseeland, Niederlande), dem Vergleich von 22 Review-Studien und Metaanalysen basierend auf Registerdaten, sowie der Auswertung der Empfehlung von Gesundheitssystemen unterschiedlicher Nationen wird eine Empfehlung generiert. Dazu wurden Reviews und Metaanalysen ausgewählt, deren Ergebnisse statistisch signifikant sind, ebenso wie die zum Zeitpunkt der Erstellung des Artikels aktuellen Jahresberichte der Endoprothesenregister. Ergebnisse Für Knieendoprothesen kann eine lange Überlebensdauer sowie ein geringeres Revisionsrisiko mithilfe einer zementierten Verankerung mit antibiotikabeladenem Knochenzement erreicht werden. Bei Patienten ab einem Alter von 70 Jahren reduziert eine zementierte Verankerung des Hüftschaftimplantats das Risiko einer intra- oder postoperativen periprothetischen Fraktur um das Vierfache, dies gilt sowohl für elektive Hüfttotalendoprothesen (Hüft-TEP), als auch für Hemiendoprothesen nach Schenkelhalsfrakturen. Ein antibiotikabeladener Knochenzement reduziert signifikant ( p = 0,041) das Risiko für das Auftreten einer periprothetischen Infektion, insbesondere bei Patienten mit Schenkelhalsfrakturen. Schlussfolgerungen Die mit antibiotikabeladenem Knochenzement versorgte Knieendoprothese ist in Deutschland etabliert und wird durch die Evidenzlage bestätigt. Registerdaten und Metaanalysen empfehlen eine zementierte Verankerung des Hüftschaftimplantats beim älteren Patienten – hier sollte die Praxis in Deutschland der aktuellen Evidenz folgen.

Background: Continuous passive motion (CPM) is frequently used during rehabilitation following total knee arthroplasty (TKA). Low-load resistance training (LLRT) using continuous active motion (CAM) devices is a promising alternative. We investigated the effectiveness of CPM compared to LLRT using the affected leg (CAMuni) and both legs (CAMbi) in the early post-operative rehabilitation. Hypotheses: (I) LLRT (CAMuni and CAMbi) is superior to CPM, (II) additional training of the unaffected leg (CAMbi) is more effective than unilateral training (CAMuni). Materials and Methods: Eighty-five TKA patients were randomly assigned to three groups, respectively: (i) unilateral CPM of the operated leg; (ii) unilateral CAM of the operated leg (CAMuni); (iii) bilateral alternating CAM (CAMbi). Patients were assessed 1 day before TKA (pre-test), 1 day before discharge (post-test), and 3 months post-operatively (follow-up). Primary outcome: active knee flexion range of motion (ROM Flex ). Secondary outcomes: active knee extension ROM (ROM Ext ), swelling, pain, C-reactive protein, quality of life (Qol), physical activity, timed-up-and-go performance, stair-climbing performance, quadriceps muscle strength. Analyses of covariances were performed (modified intention-to-treat and per-protocol). Results: Hypothesis I: Primary outcome: CAMbi resulted in a higher ROM Flex of 9.0° (95%CI −18.03–0.04°, d = 0.76) and 6.3° (95%CI −14.31–0.99°, d = 0.61) compared to CPM at post-test and follow-up, respectively. Secondary outcomes: At post-test, C-reactive protein was lower in both CAM groups compared with CPM. Knee pain was lower in CAMuni compared to CPM. Improved ROM Ext , reduced swelling, better stair-climbing and timed-up-and-go performance were observed for CAMbi compared to CPM. At follow-up, both CAM groups reported higher Qol and CAMbi showed a better timed-up-and-go performance. Hypothesis II: Primary outcome: CAMbi resulted in a higher knee ROM Flex of 6.5° (95%CI −2.16–15.21°, d = 0.56) compared to CAMuni at post-test. Secondary outcomes: At post-test, improved ROM Ext , reduced swelling, and better timed-up-and-go performance were observed in CAMbi compared to CAMuni. Conclusions: Additional LLRT of the unaffected leg (CAMbi) seems to be more effective for recovery of function than training of the affected leg only (CAMuni), which may be mediated by positive transfer effects from the unaffected to the affected limb (cross education) and/or preserved neuromuscular function of the trained, unaffected leg. Trial Registration: ClinicalTrials.gov Identifier: NCT02062138.

Total hip and knee replacements (THR, TKR) are among the most common surgeries but incidence rates vary between OECD countries. Previous studies suggested economic factors to be most influential but did not take into account health care system related factors. Hence we analysed the possible influence of healthcare system related factors on the operation rate. We used OECD data for 27 countries and calculated Age-Standardized Incidence Rates (ASIR). In order to determine possible explanatory variables on the ASIRs we performed a stepwise blockwise linear regression. The ASIR of hip and knee replacement varies widely. We identified statistically significant determinants which influence the ASIR of THR in a positive manner: incidence and length of stay of coxarthrosis, ASIR of knee replacement, health expenditures, number of nurses and an etatistic social insurance. Diabetes prevalence, gross domestic product and number of doctor consultations, however, have a negative influence on the ASIR. TKR rate is positively influenced by health expenditures and incidence rate of gonarthrosis, negatively by the number of primary practitioners. We observed strong geographic disparities in the frequency of THR and THR that cannot be explained by age structure of the countries. Economic factors seem to play a secondary role while healthcare related factors have a greater influence.

Objective: To explore differences in gait-specific long-term memory structures and actual gait performance between patients with hip osteoarthrosis, patients seen six months after total hip arthroplasty and healthy controls to gain insights into the role of the gait-specific mental representation for rehabilitation. Design: Cross-sectional study Subjects: Twenty hip osteoarthrosis patients, 20 patients seen six months after total hip arthroplasty and 20 healthy controls Methods: Spatio-temporal (gait speed, step length) and temporophasic (stance time, swing time, single support time, total double support time) gait parameters, and gait variability were measured with an electronic walkway (OptoGait). The gait-specific mental representation was assessed using the structural dimensional analysis of mental representations (SDA-M). Results: Hip osteoarthrosis patients showed significantly longer stance and total double support times, shorter swing and single support times, and a decreased gait speed as compared with healthy controls (all P < 0.01). The differences in double support times were still evident in patients seen six months after total hip arthroplasty ( P < 0.01). The gait-specific mental representation differed between hip osteoarthrosis patients and healthy controls with regard to mid-stance and mid-swing phases; the mid-stance phase was still affected six months after total hip arthroplasty (both P < 0.05). Conclusion: Our data indicated that actual gait performance and gait-specific long-term memory structures differ between hip osteoarthrosis patients and healthy controls. Important, some of these disease-related changes were still evident in patients seen six months after total hip arthroplasty.

Background:Mental fatigue is a psychobiological state induced by sustained periods of demanding cognitive activity and is characterized by feelings of tiredness which are common in everyday life. Recently, it has been hypothesized that mental fatigue might have an impact on gait performance in old adults. Therefore, the effect of mental fatigue on gait performance under single- and dual-task conditions was investigated in young and old participants.Methods:Spatio-temporal gait parameters of 16 young and 16 old healthy participants were measured using a photoelectric system during single- and dual-task walking before and after a randomly assigned mental fatigue (performing a stop-signal task for 90 minutes) and control intervention (watching a video for 90 minutes), respectively. Changes in subjective fatigue, wakefulness, mood, arousal, and psychophysiological workload (heart rate variability indices) were assessed.Results:Psychometric measures indicated increased subjective fatigue and arousal as well as decreased mood and wakefulness after the mental fatigue task. Heart rate variability indices revealed a higher psychophysiological workload during the mental fatigue intervention in old compared to young participants. Gait measures (coefficient of variation of speed, stride length, and stance time) revealed impaired dual-task walking performance following the mental fatigue intervention only in old participants.Conclusion:Data indicate that mental fatigue, induced by sustained cognitive activity, can impair gait performance during dual-task walking in old adults. The susceptibility to mental fatigue could be a new intrinsic risk factor for falls in older people and should be taken into account when dual-task gait analyses are performed.

Background and purpose — The number of hip replacements in Germany has increased considerably during the last 2 decades but lately levelled off with no significant increase in operation rates. We analyzed the future trend of hip arthroplasty and projected the number of primary hip replacements that will be performed in Germany until 2040. Patients and methods — We used prevalence data of hip arthroplasty patients from 2010 to 2016 from the nationwide inpatient statistics and population forecasts from the German Federal Bureau of Statistics up to the year 2040. We used Poisson regression to estimate the expected annual number of arthroplasty surgeries with calendar year and patient age as covariates to account for differences among age groups and changes over time. Results — The number of primary hip replacements performed in Germany in 2040 was estimated to grow by 27% to 288 x 103 (95% CI 250 x 103–332 x 103) from 2010. Projected counts were highest for patients aged 60 to 70 years. The estimated incidence rate was projected to 360 (95% CI 312–414) per 100,000 residents. However, incidence rates for individual age classes were found to be constant with a slight decrease over time for individual age classes. Interpretation — Our findings suggest a growth in the total hip arthroplasty count whereas incidence rate remained constant over age classes. We consider the future demographic change to an older population as well as the increasing life expectancy to be the main reasons for the increasing patient numbers rather than a general increase in the operation frequency.

INTRODUCTION:Knee osteoarthrosis (KOA) is commonly associated with a dysfunction of the quadriceps muscle which contributes to alterations in motor performance. The underlying neuromuscular mechanisms of muscle dysfunction are not fully understood. The main objective of this study was to analyze how KOA affects neuromuscular function of the quadriceps muscle during different contraction intensities.MATERIALS AND METHODS:The following parameters were assessed in 20 patients and 20 healthy controls: (i) joint position sense, i.e. position control (mean absolute error, MAE) at 30° and 50° of knee flexion, (ii) simple reaction time task performance, (iii) isometric maximal voluntary torque (IMVT) and root mean square of the EMG signal (RMS-EMG), (iv) torque control, i.e. accuracy (MAE), absolute fluctuation (standard deviation, SD), relative fluctuation (coefficient of variation, CV) and periodicity (mean frequency, MNF) of the torque signal at 20%, 40% and 60% IMVT, (v) EMG-torque relationship at 20%, 40% and 60% IMVT and (vi) performance fatigability, i.e. time to task failure (TTF) at 40% IMVT.RESULTS:Compared to the control group, the KOA group displayed: (i) significantly higher MAE of the angle signal at 30° (99.3%; P = 0.027) and 50° (147.9%; P < 0.001), (ii) no significant differences in reaction time, (iii) significantly lower IMVT (-41.6%; P = 0.001) and tendentially lower RMS-EMG of the rectus femoris (-33.7%; P = 0.054), (iv) tendentially higher MAE of the torque signal at 20% IMVT (65.9%; P = 0.068), significantly lower SD of the torque signal at all three torque levels and greater MNF at 60% IMVT (44.8%; P = 0.018), (v) significantly increased RMS-EMG of the vastus lateralis at 20% (70.8%; P = 0.003) and 40% IMVT (33.3%; P = 0.034), significantly lower RMS-EMG of the biceps femoris at 20% (-63.6%; P = 0.044) and 40% IMVT (-41.3%; P = 0.028) and tendentially lower at 60% IMVT (-24.3%; P = 0.075) and (vi) significantly shorter TTF (-51.1%; P = 0.049).CONCLUSION:KOA is not only associated with a deterioration of IMVT and neuromuscular activation, but also with an impaired position and torque control at submaximal torque levels, an altered EMG-torque relationship and a higher performance fatigability of the quadriceps muscle. It is recommended that the rehabilitation includes strengthening and fatiguing exercises at maximal and submaximal force levels.

2.2 Periprosthetic Joint Infections in the Spectrum of the German Diagnosis-Related Groups System – 14 Sascha Gravius and Hendrik Kohlhof 2.2.

Objective: Objectives were (1) to explore differences in gait-specific long-term memory structures and gait performance between knee osteoarthrosis patients and healthy subjects and (2) to identify the extent to which the gait-specific mental representation is associated with gait performance. Design: Cross-sectional study. Subjects: In total, 18 knee osteoarthrosis patients and 18 control subjects. Methods: Spatio-temporal (gait speed, step length) and temporophasic (stance time, swing time, single support time, total double support time) gait parameters and gait variability were measured with an electronic walkway (OptoGait). The mental representation was assessed using the structural dimensional analysis of mental representations (SDA-M). Results: (1) Patients showed significantly longer stance times (P<0.002) and total double support times, shorter swing times and single support times, a decreased gait speed (P-values<0.001) and structural differences in the gait-specific mental representation as compared with the healthy controls. (2) Correlation analyses revealed the mental representation of the human gait to be associated with actual gait performance in osteoarthrosis patients. Double support times were positively associated with the structural quality of the mental representation and step length variability was positively associated with the number of sequencing errors in the representation. Conclusion: The gait-specific mental representation and actual gait performance differ between patients with severe knee osteoarthrosis and healthy controls, and both are linked to one another. This finding suggests that musculoskeletal disorders can lead to changes in the mental representation of the gait, and as such the SDA-M could provide useful information to improve the rehabilitation following osteoarthrosis.

The Bindex(®) quantitative ultrasound (QUS) device is currently available and this study analyzed (I) its relative and absolute intra- and inter-session reliability and (II) the relationship between the data provided by Bindex(®)-QUS and the bone mineral density (BMD) measured by dual-energy x-ray absorptiometry at corresponding skeletal sites in young and healthy subjects (age: 25.0  ±  3.6 years). Bindex(®)-QUS calculates a density index on the basis of the thickness of cortical bone measured at the distal radius and the distal plus proximal tibia. The data show a very good relative and absolute intra- (ICC  =  0.977, CV  =  1.5%) and inter-session reliability (ICC  =  0.978, CV  =  1.4%) for the density index. The highest positive correlations were found between cortical thickness and BMD for the distal radius and distal tibia (r  ⩾  0.71, p  <  0.001). The data indicate that the Bindex(®)-QUS parameters are repeatable within and between measurement sessions. Furthermore, the measurements reflect the BMD at specific skeletal sites. Bindex(®)-QUS might be a useful tool for the measurement of skeletal adaptations.

The aim of this study was to compare the neuromuscular function of the plantar flexors following caffeine or placebo administration. Thirteen subjects (25 ± 3 years) ingested caffeine or placebo in a randomized, controlled, counterbalanced, double‐blind crossover design. Neuromuscular tests were performed before and 1 h after caffeine or placebo intake. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque, and neural drive to the muscles were measured. Triceps surae muscle activation was assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100 ms, 100–200 ms) and maximal voluntary contraction (MVC). Furthermore, evoked spinal reflex responses of the soleus muscle (H‐reflex evoked at rest and during MVC, V‐wave) and peak twitch torques were evaluated. The isometric maximum voluntary torque and evoked potentials were not different. However, we found a significant difference between groups for rate of torque development in the time intervals 0–100 ms [41.1 N·m/s (95% CI: 8.3–73.9 N·m/s, P = 0.016)] and 100–200 ms [32.8 N·m/s (95% CI: 2.8–62.8 N·m/s, P = 0.034)]. These changes were accompanied by enhanced neural drive to the plantar flexors. Data suggest that caffeine solely increased explosive voluntary strength of the triceps surae because of enhanced neural activation at the onset of contraction whereas MVC strength was not affected.

Total knee arthroplasty (TKA) leads to a loss of periprosthetic bone mineral density (BMD). Great importance is attached to the prevention of periprosthetic bone loss with a view to ensuring a long service life of the prosthesis. In order to provide appropriate recommendations for preventive movement therapy measures to combat peri-implant bone loss, it is necessary to know the predictors of periprosthetic BMD. The aim of this study was (1) to determine the change of periprosthetic BMD of the femur and tibia and (2) to analyse the effects of different predictors on periprosthetic BMD. Twenty-three patients with primary TKA were evaluated 10 days and 3 months postoperatively. The data analysis comprised (1) the change in periprosthetic BMD from pretest to posttest and (2) the correlations between BMD and the variables isometric maximum voluntary force, lean mass, physical activity (step count), and BMI using multiple linear regression and structural equation modelling (SEM). BMD of the distal femur was significantly reduced by 19.7% (P = 0.008) 3 months after surgery, while no changes were found in BMD of the tibia. The results of SEM demonstrate that 55% of the BMD variance was explained by the model (χ2 = 0.002; df = 1; P = 0.96; χ2/df = 0.002; RMSEA < 0.01; TLI = 1.5; CFI = 1.0). A significant direct effect was only evidenced by the variable lean mass (β = 0.38; b = 0.15; SE = 0.07; C.R. = 2.0; P = 0.046). It can be assumed that a large muscle mass with accompanying distribution of high mechanical load in the bones can contribute to local changes of periprosthetic BMD. Concrete recommendations for preventing peri-implant bone loss therefore include exercises which have the aim of maintaining or building up muscle mass.

The economization of inpatient care began when lump sum reimbursement was introduced into the hospital sector. Since then, total hip arthroplasty (THA) has experienced a rapid development in terms of annual procedures and the optimization of the clinical pathway. Therefore, it is obvious to highlight THA as one of the most common procedures in the German health care system. In this work, the two most common techniques for the fixation of THA are investigated with regard to their cost structure and their influence on the clinical result.In Germany, uncemented and hybrid fixation are used for THA. In this study we investigated the differences in material costs, the duration of surgery, and the length of stay.For each fixation technique a retrospective cost analysis was carried out, based on the data from the treatment documentation of the University Hospital for Orthopedics, Rostock (OUK). The mean values of the parameters and expenses have been reviewed with descriptive statistics for differences.With regard to total costs and the contribution margin there was no statistically significant difference.Although there are differences in individual cost areas, in total costs, cost advantages and disadvantages cancel each other out. Thus, from an economic perspective no particular technique can be recommended.

The aseptic loosening due to periprosthetic osteolysis, is a major cause for the failure of orthopaedic implants. The basic understanding of the key mechanisms of osseointegration and periprosthetic bone loss should be used for the development of pharmacological strategies to improve the periprosthetic bone mass and thus to extend the life expectancy of an implant. An example of this is the possible application of RANKL-blocking molecules in order to prevent abrasion induced osteolysis. Bisphosphonates are known to be potent anti-resorptive drugs in the treatment of osteoporosis and other bone metabolism diseases. With the use of bisphosphonates or for example PTH we have now the potential possibility to improve both bone healing as well as bony remodeling after implantation of total joint prostheses, and thus to improve the service life expectancy of the implant. In the future the local application of osteoprotectives in addition to the systemic application should be discussed as well. It is important to clarify the dose, multiple or single administration of the substances. Overall, it can however be expected to improve the survival rates of implants by the use of the possible osteoprotectives.

ZusammenfassungDie aseptische Lockerung aufgrund periprothetischer Osteolysen ist eine der häufigsten Ursachen für das Versagen von orthopädischen Implantaten. Das grundlegende Verständnis der wichtigsten Mechanismen der Osseointegration und des periprothetischen Knochenverlusts sollte für die Entwicklung von pharmakologischen Strategien zur Verbesserung der periprothetischen Knochenmasse und damit zur Verlängerung der Standzeit eines Implantats herangezogen werden. Ein Beispiel hierfür ist die mögliche Anwendung von RANKL-blockierenden Molekülen, um Abrieb-induzierte Osteolysen zu verhindern. Bisphosphonate sind potente antiresorptive Medikamente in der Behandlung von Osteoporose und anderen Erkrankungen des Knochenstoffwechsels. Mit der Verwendung von Bisphosphonaten oder von beispielsweise auch Parathormon (PTH) besteht heutzutage die potenzielle Möglichkeit, sowohl die Knochenheilung als auch die analog dazu verlaufenden knöchernen Umbauprozesse nach Implantation von Totalendoprothesen und damit die Prothesenstandzeit zu verbessern. Neben einer systemischen Applikation ist in Zukunft aber auch die lokale Applikation der Osteoprotektiva zu diskutieren. Wichtig ist hierbei die Klärung der Dosis, Mehrfach-oder Einfachapplikation der Substanzen. Insgesamt ist durch die Verwendung der möglichen Osteoprotektiva eine weitere Verbesserung der Überlebensraten von Implantaten zu erwarten.

This study investigated effects of caffeine ingestion (8 mg/kg) on maximum voluntary torque (MVT) and voluntary activation of the quadriceps during isometric, concentric and eccentric contractions. Fourteen subjects ingested caffeine and placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after oral caffeine and placebo intake. MVTs were measured and the interpolated twitch technique was applied during isometric, concentric and eccentric contractions to assess voluntary activation. Furthermore, normalized root mean square of the EMG signal was calculated and evoked spinal reflex responses (H-reflex evoked at rest and during weak isometric voluntary contraction) as well as twitch torques were analyzed. Caffeine increased MVT by 26.4 N m (95%CI: 9.3-43.5 N m, P = 0.004), 22.5 N m (95%CI: 3.1-42.0 N m, P = 0.025) and 22.5 N m (95%CI: 2.2-42.7 N m, P = 0.032) for isometric, concentric and eccentric contractions. Strength enhancements were associated with increases in voluntary activation. Explosive voluntary strength and voluntary activation at the onset of contraction were significantly increased following caffeine ingestion. Changes in spinal reflex responses and at the muscle level were not observed. Data suggest that caffeine ingestion induced an acute increase in voluntary activation that was responsible for the increased strength regardless of the contraction mode.