Biofabrication for osteochondral tissue regeneration: bioink printability requirements.

Biofabrication allows the formation of 3D scaffolds through a precise spatial control. This is of foremost importance when aiming to mimic heterogeneous and anisotropic architecture, such as that of the osteochondral tissue. Osteochondral defects are a supreme challenge for tissue engineering due to the compositional and structural complexity of stratified architecture and contrasting biomechanical properties of the cartilage-bone interface. This review highlights the advancements and retreats witnessed by using developed bioinks for tissue regeneration, taking osteochondral tissue as a challenging example. Methods, materials and requirements for bioprinting were discussed, highlighting the pre and post-processing factors that researchers should consider towards the development of a clinical treatment.

Effects of Dry-Land Strength and Conditioning Programs in Age Group Swimmers.

Amaro, NM, Marinho, DA, Marques, MC, Batalha, N, and Morouço, PG. Effects of dry-land strength and conditioning programs in age group swimmers. J Strength Cond Res 31(9): 2447-2454, 2017-Even though dry-land S&C training is a common practice in the context of swimming, there are countless uncertainties over its effects in performance of age group swimmers. The objective was to investigate the effects of dry-land S&C programs in swimming performance of age group swimmers. A total of 21 male competitive swimmers (12.7 ± 0.7 years) were randomly assigned to the Control group (n = 7) and experimental groups GR1 and GR2 (n = 7 for each group). Control group performed a 10-week training period of swim training alone, GR1 followed a 6-week dry-land S&C program based on sets and repetitions plus a 4-week swim training program alone and GR2 followed a 6-week dry-land S&C program focused on explosiveness, plus a 4-week program of swim training alone. Results for the dry-land tests showed a time effect between week 0 and week 6 for vertical jump (p < 0.01) in both experimental groups, and for the GR2 ball throwing (p < 0.01), with moderate to strong effect sizes. The time × group analyses showed that for performance in 50 m, differences were significant, with the GR2 presenting higher improvements than their counterparts (F = 4.156; p = 0.007; (Equation is included in full-text article.)= 0.316) at week 10. Concluding, the results suggest that 6 weeks of a complementary dry-land S&C training may lead to improvements in dry-land strength. Furthermore, a 4-week adaptation period was mandatory to achieve beneficial transfer for aquatic performance. Additional benefits may occur if coaches plan the dry-land S&C training focusing on explosiveness.

Tethered swimming can be used to evaluate force contribution for short-distance swimming performance.

The purpose of this study was two-fold: (a) to compare stroke and the physiological responses between maximal tethered and free front crawl swimming and (b) to evaluate the contribution of force exertion for swimming performance over short distances. A total of 34 male swimmers, representing various levels of competitive performance, participated in this study. Each participant was tested in both a 30-second maximal tethered swimming test and a 50-m free swimming test. The tethered force parameters, the swimming speed, stroke (stroke rate [SR]), and the physiological responses (increase in blood lactate concentration [ΔBLa], heart rate, and rate of perceived exertion) were recorded and calculated. The results showed no differences in stroke and the physiological responses between tethered and free swimming, with a high level of agreement for the SR and ΔBLa. A strong correlation was obtained between the maximum impulse of force per stroke and the speed (r = 0.91; p < 0.001). Multiple regression analysis revealed that the maximum impulse and SR in the tethered condition explained 84% of the free swimming performance. The relationship between the swimming speed and maximum force tended to be nonlinear, whereas linear relationships were observed with the maximum impulse. This study demonstrates that tethered swimming does not significantly alter stroke and the physiological responses compared with free swimming, and that the maximum impulse per stroke should be used to evaluate the balance between force and the ability to effectively apply force during sprint swimming. Consequently, coaches can rely on tethered forces to identify strength deficits and improve swimming performance over short distances.

Evaluation of adolescent swimmers through a 30-s tethered test.

Our purpose was to demonstrate that 30-s tethered swimming test can be a useful tool to estimate swimming performance in short distance freestyle events. Thirteen high level adolescent swimmers (7 male and 6 female of 16.6 ± 1.0 and 15.8 ± 0.8 years old) performed a 30-s maximum effort in front crawl tethered swimming. Afterward, subjects completed 50-m and 100-m freestyle events at the National Championships. Both maximum and mean force values obtained in the tethered test related directly with 50-m (r = .78 and r = .72, p < .01, respectively) and 100-m freestyle velocities (r = .63 and r = .61, p < .05, respectively). Fatigue index did not present a significant relationship with any of the studied performance variables. However, a proposed parameter--fatigue slope-correlated with 50-m (r = -.75, p < .01), 100-m performances (r = -.57, p < .05) and with r[La-] (r = -.90, p < .01). It is concluded that, for adolescent swimmers, values obtained from 30-s tethered test are well related with swimming performance in sprint events. In addition, fatigue slope seems to be more associated with swimming performance in short distance events than fatigue index.

Quantification of swimmers' ability to apply force in the water: the potential role of two new variables during tethered swimming.

This study aimed 1) to examine variables that may quantify the ability to apply force in the water and 2) to test their relationship with free swimming performance. Sixteen regional-level swimmers participated in this study. Average (Favg) and maximum (Fmax) forces were measured for 30 s arm stroke tethered swimming in a flume at zero and 1.389 m/s water flow speeds. The maximum and average force's relative changes (ΔFmax and ΔFavg, respectively) were calculated between tethered swimming at zero and 1.389 m/s water flow speeds. Free swimming speeds were obtained from 25, 50, and 100 m front crawl trials, and were correlated with ΔFmax and ΔFavg. A negative correlation was found between ΔFmax and 25, 50 and 100 m speeds (r = -0.84, r = -0.74, r = -0.55; p < 0.05, respectively) and ΔFavg correlated negatively with 25 and 50 m speeds (r = -0.63, r = -0.54; p < 0.05, respectively), but it did not correlate with 100 m swimming speed. The relative change in force could be used to quantify the ability to apply force in the water. This could aid coaches to understand if changes in swimmers' ability to apply force in the water contribute to improvements in performance.

Relationship Between Tethered Swimming in a Flume and Swimming Performance.

PURPOSE: To study the relationship between tethered swimming in a flume at different speeds and swimming performance. METHODS: Sixteen regional-level swimmers performed 25-, 50-, and 100-m front-crawl trials and four 30-s tethered-swimming tests at 0, 0.926, 1.124, and 1.389 m·s-1 water-flow velocities. Average and maximum force, average and maximum impulse, and intracyclic force variation (dF) were estimated for each tethered-swimming trial. Swimming velocity and intracyclic velocity variation (dv) were obtained for each free-swimming trial. Stroke rate and rating of perceived exertion (RPE) were registered for all trials. RESULTS: Tethered-swimming variables, both at 1.124 m·s-1 and at 1.389 m·s-1 water-flow velocities, were positively associated with 25-m swimming velocity (P < .05). Average force and maximum impulse in stationary swimming were significantly associated with 25-m swimming velocity (P < .05). A positive relationship between water-flow velocities with dF was observed. Swimming performance was not related to dF or dv. Neither stroke rate nor RPE differed between the 4 tethered conditions and mean 50-m free-swimming velocity (P > .05). CONCLUSIONS: Measuring force in a swimming flume at higher water-flow velocities is a better indicator of performance than stationary tethered swimming. It enables assessment of the ability to effectively apply force in the water.

Intracyclic Variation of Force and Swimming Performance.

CONTEXT: In front-crawl swimming, the upper limbs perform alternating movements with the aim of achieving a continuous application of force in the water, leading to lower intracyclic velocity variation (dv). This parameter has been identified as a crucial criterion for swimmers' evaluation. PURPOSE: To examine the assessment of intracyclic force variation (dF) and to analyze its relationship with dv and swimming performance. METHODS: A total of 22 high-level male swimmers performed a maximal-effort 50-m front-crawl time trial and a 30-s maximal-effort fully tethered swimming test, which were randomly assigned. Instantaneous velocity was obtained by a speedometer and force by a strain-gauge system. RESULTS: Similarity was observed between the tests, with dF attaining much higher magnitudes than dv (P < .001; d = 8.89). There were no differences in stroke rate or in physiological responses between tethered and free swimming, with a high level of agreement for the stroke rate and blood lactate increase. Swimming velocity presented a strong negative linear relationship with dF (r = -.826, P < .001) and a moderate negative nonlinear relationship with dv (r = .734, P < .01). With the addition of the maximum impulse to dF, multiple-regression analysis explained 83% of the free-swimming performance. CONCLUSIONS: Assessing dF is a promising approach for evaluating a swimmer's performance. From the experiments, this new parameter showed that swimmers with higher dF also present higher dv, leading to a decrease in performance.

The variations on the aerodynamics of a world-ranked wheelchair sprinter in the key-moments of the stroke cycle: A numerical simulation analysis.

Biomechanics plays an important role helping Paralympic sprinters to excel, having the aerodynamic drag a significant impact on the athlete's performance. The aim of this study was to assess the aerodynamics in different key-moments of the stroke cycle by Computational Fluid Dynamics. A world-ranked wheelchair sprinter was scanned on the racing wheelchair wearing his competition gear and helmet. The sprinter was scanned in three different positions: (i) catch (hands in the 12h position on the hand-rim); (ii) the release (hands in the 18h position on the hand-rim) and; (iii) recovery phase (hands do not touch the hand-rim and are hyperextended backwards). The simulations were performed at 2.0, 3.5, 5.0 and 6.5 m/s. The mean viscous and pressure drag components, total drag force and effective area were retrieved after running the numerical simulations. The viscous drag ranged from 3.35 N to 2.94 N, pressure drag from 0.38 N to 5.51 N, total drag force from 0.72 N to 8.45 N and effective area from 0.24 to 0.41 m2. The results pointed out that the sprinter was submitted to less drag in the recovery phase, and higher drag in the catch. These findings suggest the importance of keeping an adequate body alignment to avoid an increase in the drag force.

Relative Contribution of Arms and Legs in 30 s Fully Tethered Front Crawl Swimming.

The relative contribution of arm stroke and leg kicking to maximal fully tethered front crawl swimming performance remains to be solved. Twenty-three national level young swimmers (12 male and 11 female) randomly performed 3 bouts of 30 s fully tethered swimming (using the whole body, only the arm stroke, and only the leg kicking). A load-cell system permitted the continuous measurement of the exerted forces, and swimming velocity was calculated from the time taken to complete a 50 m front crawl swim. As expected, with no restrictions swimmers were able to exert higher forces than that using only their arm stroke or leg kicking. Estimated relative contributions of arm stroke and leg kicking were 70.3% versus 29.7% for males and 66.6% versus 33.4% for females, with 15.6% and 13.1% force deficits, respectively. To obtain higher velocities, male swimmers are highly dependent on the maximum forces they can exert with the arm stroke (r = 0.77, P < 0.01), whereas female swimmers swimming velocity is more related to whole-body mean forces (r = 0.81, P < 0.01). The obtained results point that leg kicking plays an important role over short duration high intensity bouts and that the used methodology may be useful to identify strength and/or coordination flaws.

Quantification of upper limb kinetic asymmetries in front crawl swimming.

This study aimed at quantifying upper limb kinetic asymmetries in maximal front crawl swimming and to examine if these asymmetries would affect the contribution of force exertion to swimming performance. Eighteen high level male swimmers with unilateral breathing patterns and sprint or middle distance specialists, volunteered as participants. A load-cell was used to quantify the forces exerted in water by completing a 30s maximal front crawl tethered swimming test and a maximal 50 m free swimming was considered as a performance criterion. Individual force-time curves were obtained to calculate the mean and maximum forces per cycle, for each upper limb. Following, symmetry index was estimated and breathing laterality identified by questionnaire. Lastly, the pattern of asymmetries along the test was estimated for each upper limb using linear regression of peak forces per cycle. Asymmetrical force exertion was observed in the majority of the swimmers (66.7%), with a total correspondence of breathing laterality opposite to the side of the force asymmetry. Forces exerted by the dominant upper limb presented a higher decrease than from the non-dominant. Very strong associations were found between exerted forces and swimming performance, when controlling the isolated effect of symmetry index. Results point that force asymmetries occur in the majority of the swimmers, and that these asymmetries are most evident in the first cycles of a maximum bout. Symmetry index stood up as an influencing factor on the contribution of tethered forces over swimming performance. Thus, to some extent, a certain degree of asymmetry is not critical for short swimming performance.