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Discusses the importance of flexibility in sports, provides exercises to improve it, and profiles athletes known for their flexibility.

PurposeStretching 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.MethodsIn 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.ResultsMeta-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).ConclusionIf 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.

Background Viscosupplementation for knee osteoarthritis (OA) aims to minimize pain and improve joint function. However, its effects on knee biomechanics during squat activities have not been investigated. This study aimed to assess the effects of viscosupplementation on squat biomechanics of older adults with late-stage knee osteoarthritis utilizing three-dimensional (3D) motion capture technology. Methods This study is a multiple-blinded, randomized, single-center, placebo-controlled trial with a 1:1 allocation ratio. Forty-two older individuals (72.6 ± 6.5 years) with advanced knee OA were randomly allocated into two groups to receive viscosupplementation or placebo (saline injection). Kinematic data were collected by a 3D motion analysis system 1 week before and 1, 6, and 12 weeks after the intervention. Dependent variables included maximal vertical displacement of center of mass (CoM), CoM position in the mediolateral axis, knee range of motion between initial and lowest CoM vertical position, and knee angles at lowest vertical CoM position in sagittal, coronal and axial planes (primary outcomes). Data were compared between groups using mixed linear models, with a significance level of 0.05. A repeated measures ANOVA was conducted within each group to assess changes over time if significant differences between groups were observed. Results The viscosupplementation group showed a statistically significant difference in maximum knee internal rotation at lowest vertical CoM position (4.1° 95%CI [0.6 to 7.5]– p  = 0.02) during squat at 12 weeks. None of the other variables showed statistically significant results ( p  > 0.05). There was no difference in knee internal rotation angle at 1, 6, or 12 weeks compared to baseline in the viscosupplementation group ( p  = 0.307). Conclusion This study suggests that a single shot of intra-articular viscosupplementation may help preserve knee biomechanics during squatting in patients with late-stage knee OA in the medium term. Future studies should explore the relationship between biomechanical improvements and clinical symptoms. Trial registration The trial was registered in the Brazilian Clinical Trials Registry (No. RBR-3n52h4). Date of registration: 08/30/2017.

PurposeThe purpose of the study was to investigate the effects of using a vibration foam roll (VFR) or a non-vibration foam roll (NVFR) on maximum voluntary isometric contraction peak torque (MVIC), range of motion (ROM), passive resistive torque (PRT), and shear modulus.MethodsTwenty-one male volunteers visited the laboratory on two separate days and were randomly assigned to either a VFR group or a NVFR group. Both interventions were performed for 3 × 1 min each. Before and after each intervention, passive resistive torque and maximum voluntary isometric contraction peak torque of the leg extensors were assessed with a dynamometer. Hip extension ROM was assessed using a modified Thomas test with 3D-motion caption. Muscle shear modulus of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was assessed with shear wave elastography (SWE).ResultsIn both groups (VFR, NVFR) we observed an increase in MVIC peak torque (+ 14.2 Nm, + 8.6 Nm) and a decrease in shear modulus of the RF (− 7.2 kPa, − 4.7 kPa). However, an increase in hip extension ROM (3.3°) was only observed in the VFR group. There was no change in PRT and shear modulus of the VL and VM, in both the VFR group and the NVFR group. Our findings demonstrate a muscle-specific acute decrease in passive RF stiffness after VFR and NVFR, with an effect on joint flexibility found only after VFR.ConclusionThe findings of this study suggest that VFR might be a more efficient approach to maximize performance in sports with flexibility demands.

PurposeThe chronic effects of unilateral foam rolling (FR) or FR with vibration (VFR) intervention on the rolling and non-rolling sides (cross-education effects) are still unclear. Thus, this study aimed to investigate the effects of unilateral 6-week FR or VFR intervention on ankle dorsiflexion range of motion (DF ROM), muscle stiffness, and muscle strength in both rolling and non-rolling sides.MethodsThirty healthy young men were randomly allocated into the FR (n = 15) or the VFR intervention group (n = 15). Participants performed three sets of unilateral FR or VFR interventions for 60 s of the calf muscles twice/week, for 6 weeks. DF ROM, gastrocnemius muscle stiffness, and maximal voluntary isometric contraction (MVIC) torque were assessed in the rolling and non-rolling sides before and after the intervention.ResultsThe DF ROM increased significantly (p < 0.05) to the same extent in the FR and VFR intervention groups on both rolling (FR: d = 0.58, VFR: d = 0.63) and non-rolling (FR: d = 0.39, VFR: d = 0.50) sides. Similarly, the passive torque at DF ROM increased significantly (p < 0.05) to the same extent in the FR and VFR intervention groups on both rolling (FR: d = 0.85, VFR: d = 0.77) and non-rolling (FR: d = 0.76, VFR: d = 0.68) sides. However, there were no significant changes in muscle stiffness and MVIC after FR and VFR interventions on both the rolling and non-rolling sides. FR and VFR interventions could increase the ROM in both the rolling and non-rolling sides but could not change muscle stiffness and strength.ConclusionsThe results showed that it is not necessarily needed to perform VFR to increase ROM in the long term.

Background Neutral mechanical alignment (MA) in total knee arthroplasty (TKA) aims to position femoral and tibial components perpendicular to the mechanical axis of the limb. In contrast, kinematic alignment (KA) attempts to match implant position to the prearthritic anatomy of the individual patient with the aim of improving functional outcome. However, comparative data between the two techniques are lacking. Questions/purposes In this randomized trial, we asked: (1) Are 2-year patient-reported outcome scores enhanced in patients with KA compared with an MA technique? (2) How does postoperative component alignment differ between the techniques? (3) Is the proportion of patients undergoing reoperation at 2 years different between the techniques? Methods Ninety-nine primary TKAs in 95 patients were randomized to either MA (n = 50) or KA (n = 49) groups. A pilot study of 20 TKAs was performed before this trial using the same patient-specific guides positioning in kinematic alignment. In the KA group, patient-specific cutting blocks were manufactured using individual preoperative MRI data. In the MA group, computer navigation was used to ensure neutral mechanical alignment accuracy. Postoperative alignment was assessed with CT scan, and functional scores (including the Oxford Knee Score, WOMAC, and the Forgotten Joint Score) were assessed preoperatively and at 6 weeks, 6 months, and 1 and 2 years postoperatively. No patients were lost to followup. We set sample size at a minimum of 45 patients per treatment arm based on a 5-point improvement in the mean Oxford Knee Score (OKS; the previously reported minimum clinically significant difference for the OKS in TKA), a pooled SD of 8.3, 80% power, and a two-sided significance level of 5%. Results We observed no difference in 2-year change scores (postoperative minus preoperative score) in KA versus MA patients for the OKS (mean 21, SD 8 versus 20, SD 8, least square means 1.0, 95% confidence interval [CI], −1.4 to 3.4, p = 0.4), WOMAC score (mean 38, SD 18 versus 35, SD 8, least square means 3, 95% CI, −3.2 to 8.9, p = 0.3), or Forgotten Joint score (28 SD 37 versus 28, SD 28, least square means 0.8, 95% CI, −9.1–10.7, p = 0.8). Postoperative hip-knee-ankle axis was not different between groups (mean KA 0.4° varus SD 3.5 versus MA 0.7° varus SD 2.0), but in the KA group, the tibial component was a mean 1.9° more varus than the MA group (95% CI, 0.8°−3.0°, p = 0.003) and the femoral component in 1.6° more valgus (95% CI, −2.5° to −0.7°, p = 0.003). Complication rates were not different between groups. Conclusions We found no difference in 2-year patient-reported outcome scores in TKAs implanted using the KA versus an MA technique. The theoretical advantages of improved pain and function that form the basis of the design rationale of KA were not observed in this study. Currently, it is unknown whether the alterations in component alignment seen with KA will compromise long-term survivorship of TKA. In this study, we were unable to demonstrate an advantage to KA in terms of pain or function that would justify this risk. Level of Evidence Level I, therapeutic study.

This study aimed to compare the cross-education effect of unilateral stretching intervention programs with two different intensities (high- vs. low-intensity) on dorsiflexion range of motion (DF ROM), muscle stiffness, and muscle architecture following a 4-week stretching intervention. Twenty-eight healthy males were randomly allocated into two groups: a high-intensity static stretching (HI-SS) intervention group (n = 14; stretch intensity 6–7 out of 10) and a low-intensity static stretching (LI-SS) intervention group (n = 14; stretch intensity 0–1 out of 10). The participants were asked to stretch their dominant leg (prefer to kick a ball) for 4 weeks (3 × week for 3 × 60 s). Before and after the intervention, the non-trained leg passive properties (DF ROM, passive torque, and muscle stiffness) of the plantar flexors and the muscle architecture of the gastrocnemius medialis (muscle thickness, pennation angle, and fascicle length) were measured. Non-trained DF ROM and passive torque at DF ROM were significantly increased in the HI-SS group (p < 0.01, d = 0.64, 50.6%, and p = 0.044, d = 0.36, 18.2%, respectively), but not in the LI-SS group. Moreover, there were no significant changes in muscle stiffness and muscle architecture in both groups. For rehabilitation settings, a high-intensity SS intervention is required to increase the DF ROM of the non-trained limb. However, the increases in DF ROM seem to be related to changes in stretch tolerance and not to changes in muscle architecture or muscle stiffness.

This study aimed to compare the acute effects of static stretching (SS) and proprioceptive neuromuscular facilitation (PNF) stretching on hamstrings flexibility and shear modulus. Sixteen recreationally active young volunteers participated in a randomized cross-over study. Participants underwent an aerobic warm-up (WU), followed by either SS or PNF stretching. Range of motion (RoM) during passive straight leg raise and active knee extension, as well as shear modulus of the biceps femoris (BF) and semitendinosus (ST) muscles, were measured at baseline, post-WU, and post-stretching. Both stretching techniques significantly increased RoM, with no differences observed between SS and PNF (p < 0.001; η2 = 0.59–0.68). However, only PNF stretching resulted in a significant decrease in BF shear modulus (time×stretching type interaction: p = 0.045; η2 = 0.19), indicating reduced muscle stiffness. No changes in ST shear modulus were observed after either stretching technique. There was no significant correlation between changes in RoM and shear modulus, suggesting that the increase in RoM was predominantly due to changes in stretch tolerance rather than mechanical properties of the muscles. These findings suggest that both SS and PNF stretching can effectively improve hamstring flexibility, but PNF stretching may additionally reduce BF muscle stiffness. The study highlights the importance of considering individual muscle-specific responses to stretching techniques and provides insights into the mechanisms underpinning acute increases in RoM.

AimPrevious stretching studies mostly investigated effects on the skeletal muscle but comprehensive explorations regarding the role of the connective tissue are scarce. Since the deep fascia has been demonstrated to be sensitive to mechanical tension, it was hypothesized that the fascia would also respond to stretching, contributing to enhanced range of motion (ROM).MethodsForty (40) recreationally active participants (male: n = 25, female: n = 15) were included in the randomized controlled cross-over trial and allocated to different groups performing 5 min static (STAT) or dynamic (DYN) plantar flexor stretching or control condition (CC) in a random order. Pre- and immediately post-intervention, muscle and fascia stiffness, as well as muscle and fascia thickness were measured using high-resolution ultrasound and strain elastography. ROM was assessed in the ankle joint via the knee to wall test (KtW) and goniometer.ResultsSTAT reduced both, muscle and fascia stiffness (d = 0.78 and 0.42, p < 0.001, respectively), while DYN did not reduce stiffness compared to the control condition (p = 0.11–0.41). While both conditions showed significant increases in the KtW (d = 0.43–0.46, p = 0.02–0.04), no significant differences to the CC were observed for the isolated ROM testing (p = 0.09 and 0.77). There was a small correlation between fascia stiffness decreases and ROM increases (r = − 0.25, p = 0.006) but no association was found between muscle stiffness decreases and ROM increases (p = 0.13–0.40).ConclusionOur study is the first to reveal stretch-induced changes in fascia stiffness. Changes of fascia`s but not muscle`s mechanical properties may contribute to increased ROM following stretching.

Background The prevalence of chronic non-specific neck pain (CNNP) is on the rise among the young adult population. We herein aimed to compare the effects of long-term specific cervical extensor training and stretching exercises on improving this chronic disorder in young adults. Methods In this prospective, randomized, controlled study, 70 participants aged 18–35 years with CNNP and cervical lordosis loss were included. The participants were assigned to undergo either specific cervical extensor training (observation group) or perform usual stretching exercises (control group). The exercise duration was set at 12 months, with 9 months at the clinic and 3 months at home. The outcome assessments included changes in the neck disability index, visual analog scale from baseline, cervical range of motion (CROM), cross-sectional areas (CSAs) of cervical extensors, and cervical curvature from baseline. The outcome measures were compared between groups at 3, 6, and 12 months of follow-up. Results All 70 participants underwent randomization, and no significant differences in demographics and baseline data were found between the two groups. The observation group showed a greater improvement in neck disability index and visual analog scale scores at the 12-month follow-up than the control group. Additionally, a more substantial increase in CROM and CSAs of cervical extensors was observed in the observation group at the 6-month and 12-month follow-ups ( P  < 0.05). Although more participants in the observation group achieved cervical lordosis at the 12-month follow-up, the difference was marginally nonsignificant (9% in the control group vs. 28% in the observation group, P  = 0.075). Conclusions In young adults with CNNP, long-term specific cervical extensor training was associated with a more significant clinically meaningful improvement in disability, pain, and CROM than stretching exercises. The increased CSAs of cervical extensors may potentially contribute to the restoration of cervical lordosis. Trial registration The study is registered at the Chinese domestic clinical trial (ChiCTR2000040009) at Chictr.org. The date of registration: November 18, 2020.