Sabine Felser

Modulation and Predictors of Periprosthetic Bone Mineral Density following Total Knee Arthroplasty

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.

Central Factors Contribute to Knee Extensor Strength Loss after 2000-m Rowing in Elite Male and Female Rowers

Purpose Despite growing interest in task-dependent alterations of central and peripheral fatigue after endurance exercise, little is known about the effect of rowing on quadriceps muscle fatigue. This study aimed to investigate central and peripheral mechanisms of fatigue after a 2000-m rowing time trial. Methods Eight competitive rowers (four males and four females, 20 ± 4 yr) performed a 2000-m time trial on an indoor rower and a control condition (sitting). The neuromuscular function of the knee extensors was analyzed before and 3 min after each experimental condition. Maximal voluntary torque, voluntary activation, and normalized root-mean-square of the EMG signal were measured during isometric and concentric contractions. Furthermore, knee extensor twitch torque and maximal M-wave amplitudes in response to electrical nerve stimulation were assessed. Results After the 2000-m rowing, there were significant reductions in isometric and concentric maximal voluntary torque of the knee extensors (−20% ± 9% and −18% ± 7%, respectively, P < 0.01). Both the voluntary activation of the knee extensors during isometric and concentric contractions decreased by 18% ± 15% (P < 0.05, respectively). The normalized muscle activity of rectus femoris was significantly reduced after rowing (P = 0.007), whereas vastus medialis and vastus lateralis muscle activities did not significantly differ from baseline values. No significant change was observed for knee extensor twitch torque in response to paired electrical stimuli after rowing. Conclusion The 2000-m rowing time trial resulted in significant knee extensor strength loss. Quadriceps muscle fatigue after high-intensity rowing exercise was explained primarily by central factors that lead to large reductions in voluntary drive.

Combined sensorimotor and resistance training for young short track speed skaters: A case study

The purpose of the study was to investigate the effects of a combined sensorimotor - resistance training on muscle strength and neuromuscular activation of selective muscles of the right ankle joint. Both treatments were performed successively in each training session. Seven short track speed skaters participated in the study. The training was performed twice a week for 12 weeks. Maximum peak torque during inversion/eversion, the associated neuromuscular activation of soleus and peroneus longus as well as eversion/inversion ratio were measured in a pre- and post-test, respectively. After the training the athletes revealed a significantly increased maximum peak torque during inversion (17.47 ± 4.37N · m vs. 23.57 ± 3.58N · m; p = 0.006) associated with a significantly increased root mean square of the EMG signal in the soleus (12.42 ± 6.09mV vs. 24.00 ± 9.37mV; p = 0.009). The eversion/inversion ratio was significantly decreased after training (0.96 ± 0.12 vs. 0.77 ± 0.11; p = 0.034). Eversion training adaptations were lower than inversion training adaptations probably due to the fact that resistance training did not contain an exercise for peroneus longus. Based on these the combined sensorimotor-resistance training is an attractive option for athletes where maximum strength, active joint stabilization and postural control plays a decisive role.

Intersession reliability of the interpolated twitch technique applied during isometric, concentric, and eccentric actions of the human knee extensor muscles

Introduction: Although it has been shown that voluntary activation (%VA) of the knee extensors during isometric contractions can be reliably assessed with the interpolated twitch technique, little is known about the reliability of %VA during concentric and eccentric muscle actions. Therefore, relative and absolute intersession reliability of quadriceps muscles %VA during different contraction modes was determined. Methods: After a familiarization session, 21 participants (17 males, 25 ± 2 yrs) completed two testing sessions. Paired supramaximal electrical stimuli were administered to the femoral nerve during isometric, concentric, eccentric MVCs, and at rest to assess %VA (stimuli were applied at 70° knee flexion). Results and discussion: Data indicate that %VA of the knee extensors can be reliably measured during isometric [intraclass correlation coefficient (ICC) = 0.89, coefficient of variation (CV) = 4.1%], concentric (ICC = 0.87, CV = 6.6%), and eccentric muscle actions (ICC = 0.86, CV = 7.0%). Muscle Nerve 56: 324–327, 2017

Relationship between strength qualities and short track speed skating performance in young athletes.

This study analyzed the relationships between isometric as well as concentric maximum voluntary contraction (MVC) strength of the leg muscles and the times as well as speeds over different distances in 17 young short track speed skaters. Isometric as well as concentric single‐joint MVC strength and multi‐joint MVC strength in a stable (without skates) and unstable (with skates) condition were tested. Furthermore, time during maximum skating performances on ice was measured. Results indicate that maximum torques during eversion and dorsal flexion have a significant influence on skating speed. Concentric MVC strength of the knee extensors was higher correlated with times as well as speeds over the different distances than isometric MVC strength. Multi‐joint MVC testing revealed that the force loss between measurements without and with skates amounts to 25%, while biceps femoris and soleus showed decreased muscle activity and peroneus longus, tibialis anterior, as well as rectus femoris exhibited increased muscle activity. The results of this study depict evidence that the skating times and speeds are primarily influenced by concentric MVC strength of the leg extensors. To be able to transfer the strength onto ice in an optimal way, it is necessary to stabilize the knee and ankle joints.

The Bindex(®) ultrasound device: reliability of cortical bone thickness measures and their relationship to regional bone mineral density.

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.

P-36 Quadriceps muscle fatigue after 2000-m rowing

Introduction Despite extensive investigations on the task-dependency of neuromuscular fatigue after several types of exercise, hardly anything is known about central and peripheral factors of fatigue after rowing. In rowing, approximately 70% of total muscle mass is involved due to the fact that upper and lower body muscles work synchronised during the rowing stroke.1 In particular, the quadriceps muscle is identified as a major contributor to propulsion of the rowing boat by pushing against the foot stretcher.2 The aim of the present study was to investigate the effect of a 2000-m rowing time-trial on indices of quadriceps muscle fatigue. Methods Eight competitive rowers (4 males, 4 females, 20 ± 4 years) performed a 2000-m time-trial on an indoor rower and a control condition (sitting). Neuromuscular function of the quadriceps muscle was analysed before and after each experimental condition. Maximal voluntary torque, voluntary activation estimated via interpolated twitch technique and normalised root mean square of the EMG signal (RMS·M–1) were assessed during maximal voluntary contractions (MVCs). Furthermore, potentiated quadriceps twitch torque and maximal M-wave amplitudes in response to electrical nerve stimulation were recorded. Results After 2000-m rowing, there were significant reductions in isometric and concentric maximal voluntary torque (–20%–18%, P < 0.01). Both voluntary activation during isometric and concentric MVCs were significantly decreased after rowing (P < 0.05). However, there was no significant change in quadriceps twitch torque after rowing. For the control condition, indices of central and peripheral fatigue were not significantly different from baseline values (all P > 0.05). Discussion The 2000-m rowing time-trial induced considerable quadriceps muscle fatigue. Data further revealed a major contribution of central factors to quadriceps muscle fatigue after rowing as indicated by significant reductions in voluntary activation and quadriceps RMS·M–1. Interestingly, previous studies have typically shown that less central, but rather peripheral mechanisms contribute to quadriceps muscle fatigue after short-duration endurance exercise [3]. We hypothesise, in this regard, that the strong impairments in voluntary drive to quadriceps are possibly related to a “spill-over” of central fatigue from the great amount of simultaneously working muscles. This effect might be attributable to the ensemble feedback of inhibitory group III/IV muscle afferents.4 References Steinacker J. J Appl Physiol1993;84:3–10. Soper C, Hume PA. Sports Med2004;34:825–48. Thomas K, et al. Med Sci Sports Exerc2015;47:537–46. Sidhu SK, et al. J Physiol2014;592:5011–24.

P-59 Relationship between autonomic cardiac regulation at rest and indices of training load in recreational cyclists

Although cycling is one of the most popular aerobic exercises in competitive and non-competitive recreational sports, limited data exist regarding the acute physiological responses to a period of intensified training in recreational cyclists. Increases in training load typically occur, however in annual training camps. Thus, the aims of this observational field study were to (i) assess short-term autonomic, haematological and muscular responses to increased training load in recreational active male cyclists; and (ii) to elucidate, whether there is a correlation between autonomic response and indices of training load in this population. It was hypothesised, that an increase of aerobic training volume leads to significant elevations of serum creatine kinase (S-CK), increases in morning heart rate, and alterations of indices of heart rate variability (HRV). Methods: Heart rate (HR) and its variability (HRV), serum creatine kinase (S-CK) and hematocrit (Hct) were measured in the mornings before (PRE) and following three consecutive training days (POST 1-3). Daily cycling distance, altitude difference, maximum temperature of the day differed between the training sessions and were: 105 km, 1800 m, 26°C for training day 1; 122 km, 1700 m, 20°C for training day 2, and 80 km, 1900 m, 20°C for training day 3, respectively. Results: Morning HR significantly increased during the training period (PRE: 52.2±6.7 bpm, POST 1: 58.8±7.0 bpm POST 2: 58.5±8.1 bpm, POST 3: 57.9±7.2 bpm; F(3,33) = 11.182, p < 0.001, partial η2 = 0.554). While the parasympathetically modulated HRV high frequency power (HFP) decreased from PRE to POST 1-3, no significant effect was found for normalised low frequency power (LFP n.u.; PRE: 0.60±0.23, POST 1: 0.74±0.13, POST 2: 0.69±0.20, POST 3: 0.68±0.21; F(3,33) = 2.287, p = 0.101, partial η2 = 0.203), a measure reflecting sympathetic HR modulation. Hct showed a progressive decrease across measurement days (PRE: 49.9±4.0%, POST 1: 46.5±5.1%, POST 2: 45.5±3.8%, POST 3: 43.2±3.4%; F(3,33) = 11.909, p < 0.001, partial η2 = 0.520). Average S-CK increased after the training, with three subjects showing above reference values at POST 1 and 2 (PRE: 90.0±32.1 U/L, POST 2: 334.7±487.6 U/L, POST 3: 260.1±303.4 U/L, POST 3: 225.1±258.8 U/L; (F(3,33) = 3.996, p = 0.017, partial η2 = 0.285). S-CK leakage was significantly associated with HR (r=0.452, p=0.002) and HFP after night rest (r=-0.492, p<0.001). Conclusion: Three days of increased aerobic training volume can be associated with hemodilution, parasympathetic withdrawal and increases in muscular damage seromarkers in recreational cyclists. Despite cycling is thought to be an activity inducing no or only minor elevations in seromarkers of muscular damage (Noakes, 1987), an intensified training period increased S-CK in our sample of recreational cyclists. At POST 2 S-CK value tended to decrease, possibly due to a repeated bout effect (McHugh, 2003). Morning HR and its variability reflected larger alterations in training load in our study. Furthermore, S-CK, a marker of muscular damage and/or training load, was associated with alterations of HR-derived indices of autonomic control, a finding that has been previously reported by only a few investigators (Buchheit et al., 2011).