Post-Activation-Performance Enhancement: Possible Contributing Factors.

This study aimed to narrow down the possible mechanisms of Post-Activation Performance Enhancement (PAPE), especially if they are exclusively found in the muscle. It was therefore investigated whether (1) the PAPE effect is influenced by neural factors and (2) if Post-Activation-Potentiation (PAP) influences PAPE. Thirteen strength-trained participants (26.5 ± 3.2 years) took part in at least one of three interventions (PAP, PAPE-Electrical (PAPEE), and PAPE-Voluntary (PAPEV)). Conditioning contractions (CC) and testing involved isometric knee extensions performed on an isokinetic device at an 80° knee flexion angle. The CC was either performed voluntarily (PAP, PAPEV) or was evoked through electrical stimulation (PAPEE). Testing was performed at baseline and after two seconds, four minutes, eight minutes, and twelve minutes of the CC. Maximum voluntary isometric contractions (MVIC) for the PAPE trials and supramaximal twitches for the PAP trial were used for testing. Parameters of interest were peak torque and rate of torque development (RTD), and electromyography (EMG) amplitude of the quadriceps (only PAPE). Repeated measures ANOVA and simple contrast comparisons were used for statistical analysis. Peak torque (p < 0.001, η2p = 0.715) and RTD (p = 0. 005, η2p = 0.570) increased significantly during the PAP protocol immediately two seconds after the CC and decreased to near baseline values for the following time points (p > 0.05). Peak torque, RTD, and peak EMG showed no significant differences during PAPEE and PAPEV trials (p > 0.05). Due to the lack of a visible PAPE effect, the question of whether neural mechanisms influence PAPE cannot be answered. Due to the time course of the PAP analysis, it is questionable if these mechanisms play a role in PAPE. The assumption that the PAP mechanism influences PAPE cannot be confirmed for the same reason.

Testing the Posterior Chain: Diagnostic Accuracy of the Bunkie Test versus the Isokinetic Hamstrings/Quadriceps Measurement in Patients with Self-Reported Knee Pain and Healthy Controls.

(1) Background: The isokinetic measurement (IM) of the leg muscles is well established but costly, whereas the Bunkie Test (BT) is a rarely investigated but easy-to-conduct functional test to evaluate the total posterior chain. Although the tests differ in aim and test structures, both have their justification in the assessment process. Therefore, this study evaluated the diagnostic accuracy of the BT and the IM. (2) Methods: 21 participants (9 female, 12 male; age, 26.2 ± 5.26 years; weight 73.8 ± 14.6 kg; height 176.0 ± 9.91 cm) and 21 patients (9 female, 12 male; age, 26.5 ± 5.56 years; weight, 72.6 ± 16.9 kg; height 177.0 ± 10.1 cm) with self-reported pain in the knee performed the IM and the BT. For IM, we calculated the ratio of the knee mean flexor/extensor peak torque (H/Q ratio) for 60°/s and 120°/s, and BT performance was measured in seconds. We classified the IM (<0.6 H/Q ratio) and the BT (leg difference ≥4 s) as binary results according to the literature. We calculated the sensitivity and specificity, which we compared with the Chi-Square test, and the 95% confidence intervals (CI). A p-value of ≤0.05 is considered significant. (3) Results: The sensitivity for the BT was 0.89, 95% CI [0.67, 0.99], and the specificity was 0.52 [0.30, 0.74]. For the IM, the sensitivity was 0.14 [0.03, 0.36] for 60°/s and 0.05 [0.00, 0.24] for 120°/s, and the specificity was 0.70 [0.46, 0.88] for 60°/s and 0.90 [0.68, 0.99] for 120°/s. The results of the Chi-Square tests were significant for the BT (χ2 (1) = 6.17, p = 0.01) but not for the IM (60°/s: χ2 (1) = 0.70, p = 0.40; 120°/s: χ2 (1) = 0.00, p = 0.97). (4) Conclusions: Patients were more likely to obtain a positive test result for the BT but not for the IM.

The Relationship Between Lower Limb Passive Muscle and Tendon Compression Stiffness and Oxygen Cost During Running.

Studies have reported that a stiff triceps surae muscle and tendon-aponeurosis and also a more compliant quadriceps muscle and tendon-aponeurosis, are related to lower oxygen cost during running. However, to date, no study has investigated in a single experiment how oxygen cost during running is related to the stiffness of the free tendons (Achilles tendon, patellar tendon) and all the superficial muscles of two major muscle groups for running (i.e., quadriceps, triceps surae). Thus, 17 male trained runners/triathletes participated in this study and visited the laboratory on three occasions. On the first day, the participants were familiarized with the tests. On the second day, the passive compression stiffness of the triceps surae muscle (i.e., gastrocnemii), Achilles tendon, quadriceps muscle (i.e., vastii, rectus femoris), and patellar tendon was non-invasively measured using a digital palpation device (MyotonPRO). In addition, an incremental test was applied to test the VO2max of the participants. Thereafter, in the third visit, after at least 48-h of rest, participants performed a 15-min run on the treadmill with a speed reflecting a velocity of 70% VO2max, to assess oxygen costs during running. The Spearman correlation showed a significant negative correlation between passive Achilles tendon compression stiffness and running oxygen consumption, with a large effect size (rρ = -0.52; CI (95%) -0.81 to -0.33; P = 0.03). Moreover, no further significant relationship between oxygen cost during running and the passive compression stiffness of the quadriceps muscle and patellar tendon, as well as the triceps surae muscle, was detected. The significant correlation indicates that a stiffer passive Achilles tendon can lead to a lower oxygen cost during running. Future studies will have to test the causality of this relationship with training methods such as strength training that are able to increase the Achilles tendon stiffness.

A comparison of a single bout of stretching or foam rolling on range of motion in healthy adults.

PURPOSE: Stretching and foam rolling are common warm-up exercises and can acutely increase the range of motion (ROM) of a joint. However, possible differences in the magnitude of change on ROM between these two interventions on the immediate and prolonged effects (e.g., 10 min after the intervention) are not yet well understood. Thus, the purpose of this review was to compare the immediate and prolonged effects of a single bout of foam rolling with a single bout of stretching on ROM in healthy participants. METHODS: In total, 20 studies with overall 38 effect sizes were found to be eligible for a meta-analysis. For the main analysis, subgroup analysis, we applied a random-effect meta-analysis, mixed-effect model, respectively. The subgroup analyses included age groups, sex, and activity levels of the participants, as well as the tested muscles, the duration of the application, and the study design. RESULTS: Meta-analyses revealed no significant differences between a single stretching and foam rolling exercise immediately after the interventions (ES = 0.079; P = 0.39) nor a difference 10 min (ES = - 0.051; P = 0.65), 15 min (ES = - 0.011; P = 0.93), and 20 min (ES = - 0.161; P = 0.275) post-intervention. Moreover, subgroup analyses revealed no other significant differences between the acute effects of stretching and foam rolling (P > 0.05). CONCLUSION: If the goal is to increase the ROM acutely, both interventions can be considered as equally effective. Likely, similar mechanisms are responsible for the acute and prolonged ROM increases such as increased stretch tolerance or increased soft-tissue compliance.

Residual force enhancement in humans: Is there a true non-responder?

When an active muscle is stretched and kept isometrically active, the resulting force is enhanced compared to a purely isometric reference contraction at the same muscle length and activity; a generally accepted muscle property called residual force enhancement (rFE). Interestingly, studies on voluntary muscle action regularly identify a significant number of participants not showing rFE. Therefore, the aim was to unmask possible confounders for this non-responsive behavior. Ten participants performed maximum voluntary isometric plantarflexion contractions with and without preceding stretch. Contractions were accompanied by the assessment of voluntary activation using the twitch-interpolation technique. The same test protocol was repeated four additional times with a least on day rest in-between. Additionally, at the first and fifth sessions, a submaximal tetanic muscle-stimulation condition was added. At both muscle-stimulation sessions mean rFE higher 10% (p < 0.028) was found. In contrast, during voluntary muscle action, individual participants showed inconsistent rFE across sessions and only one session (#3) had significant rFE (5%; p = 0.023) in group means. As all participants clearly had rFE in electrical stimulation conditions, structural deficits cannot explain the missing rFE in voluntary muscle action. However, we also did not find variability in voluntary activation levels or muscle activity as the confounding characteristics of "non-responders."

Effect of legroom proportions and individual factors for sitting with crossed legs: implications on the interior design of automated driving vehicles.

Sitting with crossed legs is a commonly adopted sitting posture in everyday situations. Yet, little is known about suitable design criteria to facilitate such a position inside a vehicle. This study is aimed at determining how much space is necessary for crossing the legs while considering legroom restrictions, anthropometric measures, and individual flexibility. More specifically, 3 D-kinematics of an ankle-on-knee leg-crossing task and the easiness to move ratings of 30 participants were assessed with restrictions of the legroom (2 heights × 3 distances) as well as without restrictions. Functional regression models revealed adaptations to a legroom restriction in the execution of movement, which occurred mainly in the knee joint and increased with more restricted legroom proportions. Therefore, the present study suggests a distance of 120% of the buttock-knee length between the dashboard and the occupant, as it requires only moderate adaptations and does not affect the perceived easiness of move. Practitioner Summary: This research investigated how much space is needed to cross the legs while sitting in a vehicle, finding that the movement execution is affected by legroom proportions, as well as individual anthropometry and flexibility. The study further presents the use of predicted motion traces to determine spatial requirements of movements. Abbreviations: BKL: buttock-knee length; H-point: hip point.

Automated driving: A biomechanical approach for sleeping positions.

Occupants of autonomous vehicle have frequently indicated the desire to sleep or rest while driving, yet little has been known regarding the suitable design criteria for a biomechanically reasoned in-vehicle sleeping position. This study was aimed at evaluating the biomechanical quality of different backrest and seat pan angle combinations, and at predicting the most favourable sleeping positions based on vehicle restriction. More specifically, the interface pressure distribution and subjective suitability rating of 23 subjects was assessed in a total of nine (3 × 3) combinations of seat pan (20°, 30°, 40°) and backrest (145°, 155°, 165°) angles. Biomechanical quality was evaluated with an interface pressure score (IPS) based on sensitivity weighted pressures and the total contact area. Two-way repeated measures ANOVA revealed that IPS significantly improves with increasing seat pan angle whereas backrest angles of 155° or 165° lead to significant better IPS compared to flatter ones (145°). The overall highest IPS was observed for a 40°-seat pan angle in combination with a 155°-backrest angle. Subjective suitability rating revealed that people prefer a combination of 165° backrest angle with a seat pan of 20°; however, eight of nine combinations can be considered as suitable for sleeping. Therefore, the combination of a 40°-seat pan angle and 155° backrest is recommended by the present study for an in-vehicle sleeping position due to the increased biomechanical quality.

The Relationship between General Upper-Body Strength and Pole Force Measurements, and Their Predictive Power Regarding Double Poling Sprint Performance.

In recent years, there is an increasing importance of double poling (DP) performance regarding the outcome in classic cross-country skiing (XCS) races. So far, different approaches were used to predict DP performance but there is a lack of knowledge how general strength parameters are related to DP performance parameters gathered from in field-test situations. Therefore, the aim of this study was to determine the relationship between general strength measurements of different upper-body segments and pole force measurements during a DP sprint exercise. In addition, multiple linear regressions were calculated to determine the predictive power of theses variables regarding DP sprint performance, represented as maximum velocity. Thirteen none-elite cross-country skiers performed two 60 m DP sprints at maximal speed on a tartan track using roller skis. In addition, maximum isometric and concentric strength tests were performed on a motor-driven dynamometer with four major upper-body segments (trunk flexion / extension, shoulder / elbow extension). Especially the mean pole force and the strength test parameters correlated significantly (r ≥ 0.615) in all except one comparison. However, regression analyses revealed that neither pole force parameters (R² = 0.495) nor isometric (R² = 0.456) or dynamic (R² = 0.596) strength test parameters could predict the DP performance significantly. This study showed that standardized isokinetic strength tests could be used to estimate pole force capabilities of XCS athletes. However, pole-force and strength test parameters failed to predict significantly maximal velocity during a DP sprint exercise, which might be attributed to the non-elite subject group.