Pedro Mil-Homens

Effect of 8-Week High-Intensity Stretching Training on Biceps Femoris Architecture

Abstract Freitas, SR and Mil-Homens, P. Effect of 8-week high-intensity stretching training on biceps femoris architecture. J Strength Cond Res 29(6): 1737–1740, 2015—Previous studies have reported no changes on muscle architecture (MA) after static stretching interventions; however, authors have argued that stretching duration and intensity may not have been sufficient. A high-intensity stretching intervention targeting the knee flexors with an 8-week duration was conducted to observe the effects on biceps femoris long head (BF) architecture. Participants (n = 5) performed an average of 3.1 assisted-stretching sessions per week, whereas a control group (n = 5) did not perform stretching. The knee extension passive maximal range of motion (ROM), and BF fascicle length (FL), fascicle angle, and muscle thickness were assessed before and after the intervention. A significant increase was observed for FL (+12.3 mm, p = 0.04) and maximal ROM (+14.2°, p = 0.04) for the stretching group after the intervention. No significant changes were observed for the control group in any parameter. An 8-week high-intensity stretching program was observed to efficiently increase the BF FL, as well as the knee extension maximal ROM. Stretching intensity and duration may play an important role on MA adaptation.

Responses to static stretching are dependent on stretch intensity and duration.

Information regarding the effects of stretching intensity on the joint torque–angle response is scarce. The present study examined the effects of three static stretching protocols with different intensities and durations on the passive knee extension torque–angle response of seventeen male participants (age ± SD: 23·9 ± 3·6 years, height: 177·0 ± 7·2 cm, BMI: 22·47 ± 1·95 kg·m2). The stretching intensity was determined according to the maximal tolerable torque of the first repetition: fifty per cent (P50), seventy‐five per cent (P75) and the maximum intensity without pain (P100). Five repetitions were performed for each protocol. The stretch duration of each repetition was 90, 135 and 180 s for P100, P75 and P50, respectively. The rest period between repetitions was 30 s. Passive torque at a given angle, angle, stress relaxation, area under the curve, surface electromyography activity and visual analogue scale score were compared. The significant (P<0·05) results found were as follows: (i) the P50 and P75 did not increase the angle and passive peak torque outcomes, despite more time under stretch; (ii) only the P100 increased the angle and passive peak torque outcomes; (iii) the perception of stretching intensity mainly changed depending on knee angle changes, and not passive torque; (iv) the P50 induced a higher passive torque decrease; (v) when protocols were compared for the same time under stretch, the torque decrease was similar; (vi) the change in torque–angle curve shape was different depending on the stretching protocol. In conclusion, higher stretch duration seems to be a crucial factor for passive torque decrease and higher stretch intensity for maximum angle increase.

Are Rest Intervals between Stretching Repetitions Effective to Acutely Increase Range of Motion

UNLABELLED Static stretching with rest between repetitions is often performed to acutely increase joint flexibility. PURPOSE To test the effects of the lack of resting between stretching repetitions and the minimal number of stretching repetitions required to change the maximal range of motion (ROM), maximal tolerated joint passive torque (MPT), and submaximal passive torque at a given angle (PT). METHODS Five static stretching repetitions with a 30-s rest-interval (RI) and a no-rest-interval (NRI) stretching protocol were compared. Participants (N=47) were encouraged to perform the maximal ROM without pain in all the repetitions. Each repetition lasted 90 s. Maximal ROM, MPT, PT, and muscle activity were compared between protocols for the same number of stretching repetitions. RESULTS The NRI produced a higher increase in maximal ROM and MPT during and after stretching (P<.05). PT decreased in both protocols, although the NRI tended to have a lower decrement across different submaximal angles (.05<P<.08) in the initial range of the torque-angle curve. Significant changes in maximal ROM (P<.01) and PT (P<.01) were obtained at the 3rd and 2nd repetitions of RI, respectively. The RI did not significantly increase the MPT (P=.12) after stretching; only the NRI did (P<.01). CONCLUSIONS Lack of rest between repetitions more efficiently increased the maximal ROM and capacity to tolerate PT during and after stretching. The use of 30 s rest between repetitions potentiates the decrease in PT. Rest intervals should not be used if the aim is to acutely increase maximal ROM and peak passive torque.

The association between conventional and dynamic control knee strength ratios in elite soccer players

BACKGROUND: The isokinetic hamstrings to quadriceps (H:Q) dynamic control ratio (DCR) is frequently used to assess muscle imbalances and to screen for potential risks of knee injuries in sports. OBJECTIVE: To investigate the correlation between knee conventional ratio (CR) and DCR in elite soccer players and check for a possible relationship. A positive correlation would indicate that the CR could predict DCR. METHODS: One hundred and thirteen Brazilian elite soccer players (25.2 ± 5.3 yrs) performed maximal dominant and nondominant knee concentric (CON) and eccentric (ECC) strength tests at 60◦/s on an isokinetic dynamometer in order to calculate CR and DCR. RESULTS:A significant positive correlation between ratios was found for the dominant and non-dominant knees (r = 0.54 and 0.62; p < 0.001 which translated into low R values of 0.29 and 0.39, respectively. CONCLUSION: This suggests that the CR may not replace the DCR and is thus of a limited clinical value in assessing knee muscles imbalance. On the other hand, the paper presents for the first time a robust reference frame for the isokinetic strength and related ratios of the two major knee muscles in soccer players.

Stretching Effects: High-intensity & Moderate- duration vs. Low-intensity & Long-duration

This study examined whether a high-intensity, moderate-duration bout of stretching would produce the same acute effects as a low-intensity, long-duration bout of stretching. 17 volunteers performed 2 knee-flexor stretching protocols: a high-intensity stretch (i. e., 100% of maximum tolerable passive torque) with a moderate duration (243.5 ± 69.5-s); and a low-intensity stretch (50% of tolerable passive torque) with a long duration (900-s). Passive torque at a given sub-maximal angle, peak passive torque, maximal range of motion (ROM), and muscle activity were assessed before and after each stretching protocol (at intervals of 1, 30 and 60 min). The maximal ROM and tolerable passive torque increased for all time points following the high-intensity stretching (p<0.05), but not after the low-intensity protocol (p>0.05). 1 min post-stretching, the passive torque decreased in both protocols, but to a greater extent in the low-intensity protocol. 30 min post-test, torque returned to baseline for the low-intensity protocol and had increased above the baseline for the high-intensity stretches. The following can be concluded: 1) High-intensity stretching increases the maximal ROM and peak passive torque compared to low-intensity stretching; 2) low-intensity, long-duration stretching is the best way to acutely decrease passive torque; and 3) high-intensity, moderate-duration stretching increases passive torque above the baseline 30 min after stretching.

Peak Vertical Jump Power as a Marker of Bone Health in Children.

The objective of this investigation was to evaluate the accuracy of peak vertical jump power (VJP) to identify children with bone mineral density (BMD) below average, defined as BMD measured by DXA and adjusted for body height at the whole body less head≤- 1.0 standard deviation (SD). The sample included 114 boys and girls aged 8.5±0.4 years old. VJP was estimated from a countermovement jump performed on a contact mat using the measured flight time to calculate the height of rise of the center of gravity. Logistic regression analysis revealed that the odds ratio of having BMD≤1.0 SD decreased 1.2% per watt of power and the probability of BMD below average was 75.6% higher in boys than in girls with the same peak power jump. Receiver operating characteristic analysis showed that the best trade-off between sensitivity and specificity to identify children with BMD<- 1.0 SD was 635 watts in boys (sensitivity=63.3%; specificity=69.2%; AUC=0.816, 95% CI: 0.681-0.95; p<0.001) and 515 watts in girls (sensitivity=75.0%; specificity=77.0%; AUC=0.849, 95% CI: 0.698-0.999; p=0.002). These cut-off values correspond to a vertical jump of 19.9 cm and 20.5 cm in 8-year-old boys and girls, respectively. The VJP showed a reasonable sensitivity and specificity as well good discriminant ability to identify children with BMD below average.

A New Tool to Assess the Perception of Stretching Intensity.

Abstract Freitas, SR, Vaz, JR, Gomes, L, Silvestre, R, Hilário, E, Cordeiro, N, Carnide, F, Pezarat-Correia, P, and Mil-homens, P. A new tool to assess the perception of stretching intensity. J Strength Cond Res 29(9): 2666–2678, 2015—This study aimed to develop a valid and reliable scale to assess the perception of stretching intensity below and above the maximal range of motion. Experiments were conducted through a passive leg extension angle-torque assessment to healthy population (n = 90). In the studys first phase, the visual, numerical, and description of the stretching intensity scale (SIS) components were developed. The visual analog scale (VAS) score, absolute magnitude estimation (AME) score, and verbal stretching intensity symptom descriptors were assessed for different stretching intensities. In the second phase, the SIS was tested for validity, reliability, scale production, and estimation properties as well as responsiveness to stretching. In the first phase, a high correlation was found between SIS score and range of motion (ROM), as well as SIS and torque in both submaximal (intraclass correlation coefficient [ICC] = 0.89–0.99, r 2 = 0.88–0.99) and supramaximal (ICC = 0.75–0.86, r 2 = 0.68–0.88) stretching intensities. The AME and VAS scores fitted well in an exponential model for submaximal stretching intensities (y = 14.829e0.0187x , ICC = 0.97 [0.83–0.99], r 2 = 0.98), and in a linear model for supramaximal stretching intensities (y = 0.7667x − 25.751, ICC = 0.97 [0.89–0.99], r 2 = 0.9594). For the second phase, a high correlation was found between SIS score and ROM (r = 0.70–0.76, ICC = 0.76–0.85), as well as SIS and torque (r = 0.62–0.88, ICC = 0.57–0.85). The interday reliability was high to produce (r = 0.70, ICC = 0.70 [0.50–0.83]) or estimate (r = 0.89, ICC = 0.89 [0.82–0.93]) stretching intensities. The acute stretching effects on ROM and passive torque were detectable using the SIS. It is expected a high application in assessing the stretch intensity using the SIS in future studies and practical interventions.

Hamstring-to-quadriceps fatigue ratio offers new and different muscle function information than the conventional non-fatigued ratio

Commonly used injury risk prediction tests such as the hamstring‐to‐quadriceps (H:Q) strength ratio appear to be poor predictors of non‐contact injury. However, these tests are typically performed in a non‐fatigued state, despite accumulated fatigue being an important risk factor for both hamstring strain (HS) and anterior cruciate ligament (ACL) injuries in professional soccer players. After the effect of different H:Q calculation methods were compared and contrasted, the influence of neuromuscular fatigue on the H:Q strength ratio and the association between fatigued and non‐fatigued ratio scores were examined. Thirty‐five professional soccer players performed a 30‐repetition isokinetic fatigue test protocol. Peak knee joint moments were computed for each repetition, and the H:Q conventional ratio (H:QCR) was calculated using several different, previously published, methods. Knee extensor and flexor moments were statistically decreased by the sixth repetition and continued to decrease until the end of the protocol. However, the H:Q ratio was statistically decreased at the end of the test due to a significant reduction in knee flexor moment (correlation between change in knee flexor moment and change in H:Q, r≈.80; P<.01). Moreover, H:Q measured in fatigue (ie, H:QFatigue) at the end of the test was greater than H:QCR (1.25‐1.38 vs 0.70, P<.01), these variables were weakly correlated (r=.39, P=.02), and subject rankings within the cohort based on H:QCR and H:QFatigue were different (rs=0.25, P=.15). The present data suggest that H:Q ratio measurement during a fatiguing test (H:QFatigue) provides different outcomes to the traditional H:QCR. The observed significant hamstring fatigue and the difference, and weak correlation, between H:QCR and H:QFatigue indicate that useful information might be obtained with respect to the prediction of HS and ACL injury risk. The potential predictive value of H:QFatigue warrants validation in future prospective trials.

Ultrasonographic Measurement of the Biceps Femoris Long‐Head Muscle Architecture

Biceps femoris long‐head architectural assessment using ultrasonography (US) has not been previously described in detail for both acquisition (image capture) and digitization (image measurement) processes, and the effect of the US window width is unknown. This study aimed to describe the reliability and test‐retest minimum detectable difference of US‐based biceps femoris architectural measurements.

Lower limb body composition is associated to knee passive extension torque-angle response

PurposePeople vary in flexibility regarding maximum joint angle, resistance to stretch and mechanical responses during stretching exercises. Body composition (BC) has been been mentioned as one of the factors for flexibility differences. The aim of this study was to determine how body composition and anthropometric measures of the lower limb is associated with passive knee extension (PKE) torque-angle (T-A) response.MethodsTwenty-five male subjects with poor flexibility performed a maximal PKE repetition (velocity of 2°/s; 90 seconds in the static phase). Knee passive T-A, vastus medialis and semitendinosous electromyographic activity were recorded during the protocol. Viscoelastic stress relaxation (VSR) amplitude, knee passive stiffness (KPS), lower limb body composition assessed by dual energy x-ray absorptiometry, and anthropometry measures were determined.ResultsThigh skeletal muscle and bone mass, as well as thigh perimeter, showed a moderated correlation with passive torque (r = 0.45; r = 0.6; r = 0.59, respectively), joint angle (r = 0.46; r = 0.5; r = 0.5), and VSR (r = 0.46; r = 0.49; r = 0.5). Thigh skeletal muscle was also correlated with KPS (r = 0.42). All these correlations were statistically significant (p < 0.05).ConclusionsPassive knee extension T-A was found to be moderately correlated with lower limb BC. In particular, thigh perimeter and skeletal muscle mass were associated with knee passive stiffness and viscoelastic stress relaxation. More research is needed to understand what influences joint maximum angle, resistance to stretch and mechanical response to stretching.