Faster Movement Speed Results in Greater Tendon Strain during the Loaded Squat Exercise

Force-Velocity Profiling During the Braking Phase of Countermovement Jump: Relationship to Eccentric Strength and Validity of the 2-Point Method

ABSTRACT

Nishiumi, D, Yamaguchi, S, Kurokawa, T, Wakamiya, K, and Hirose, N. Force-velocity profiling during the braking phase of countermovement jump: Relationship to eccentric strength and validity of the 2-point method. J Strength Cond Res 37(11): 2141-2148, 2023-The aims of this study were threefold: to investigate the force-velocity profile during the braking phase (bFVP) of the countermovement jump (CMJ) and its relationship with other performance indicators, and whether it could be measured using the two-point method. Sixteen trained men performed 6 different loaded CMJs (0%, 32 kg, 60, 80, 100, and 120% body mass), and eccentric strength measurements were determined. Scatter plots were created using the mean force and velocity during the braking phase of each loaded CMJ. The corrected Akaike's information criterion (AICc) was calculated by fitting linear, quadratic, and cubic regression equations to the bFVP and compared using the 1-way analysis of variance and Bonferroni's post hoc tests. A correlation analysis was performed between the bFVP and other performance indicators. A bias assessment was performed to validate the 2-point method of the bFVP. The significance level was set at p < 0.05. The AICc in the linear regression equation was significantly lower (p < 0.05) than those in the other regression equations. Significant correlations were found between the slope and theoretical maximum force of the bFVP obtained from the linear regression equation and eccentric 1 repetition maximum. The acceptable condition for bias was met by 0-120%. The bFVP is likely to have a linear relationship and can be associated with eccentric strength. Furthermore, the 2-point method in bFVP has validity.

Modelling and in vivo evaluation of tendon forces and strain in dynamic rehabilitation exercises: a scoping review

OBJECTIVES

Although exercise is considered the preferred approach for tendinopathies, the actual load that acts on the tendon in loading programmes is usually unknown. The objective of this study was to review the techniques that have been applied in vivo to estimate the forces and strain that act on the human tendon in dynamic exercises used during rehabilitation.

DESIGN

Scoping review.

DATA SOURCES

Embase, PubMed, Web of Science and Google Scholar were searched from database inception to February 2021.

ELIGIBILITY CRITERIA

Cross-sectional studies available in English or Spanish language were included if they focused on evaluating the forces or strain of human tendons in vivo during dynamic exercises. Studies were excluded if they did not evaluate tendon forces or strain; if they evaluated running, walking, jumping, landing or no dynamic exercise at all; and if they were conference proceedings or book chapters.

DATA EXTRACTION AND SYNTHESIS

Data extracted included year of publication, study setting, study population characteristics, technique used and exercises evaluated. The studies were grouped by the types of techniques and the tendon location.

RESULTS

Twenty-one studies were included. Fourteen studies used an indirect methodology based on inverse dynamics, nine of them in the Achilles and five in the patellar tendon. Six studies implemented force transducers for measuring tendon forces in open carpal tunnel release surgery patients. One study applied an optic fibre technique to detect forces in the patellar tendon. Four studies measured strain using ultrasound-based techniques.

CONCLUSIONS

There is a predominant use of inverse dynamics, but force transducers, optic fibre and estimations from strain data are also used. Although these tools may be used to make general estimates of tendon forces and strains, the invasiveness of some methods and the loss of immediacy of others make it difficult to provide immediate feedback to the individuals.

The center of pressure position in combination with ankle dorsiflexion and trunk flexion is useful in predicting the contribution of the knee extensor moment during double-leg squatting

Background

Squatting exercises are commonly used in rehabilitation for knee joint disorders; in these exercises, control of knee extensor moment is important to enhance training effects and to avoid adverse effects. Ankle dorsiflexion and trunk flexion are widely used to reduce knee extensor moments during squatting, but the increased load on the low back is a concern. The purpose of this study was to determine whether the anterior–posterior (AP) center-of-pressure (COP) position and the AP-COP position in combination with ankle dorsiflexion and trunk flexion angles can predict the contribution of the knee extensor moment during double-leg squatting.

Methods

Twenty-eight healthy individuals (14 female and 14 male participants, age 22.8 ± 1.3 years) performed three sets of five consecutive double-leg squats. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system with force plates. Univariate and multivariate regression analyses were performed to predict the contribution of the knee extensor moment (% total support moment) from AP-COP position, ankle dorsiflexion, and trunk flexion.

Results

The AP-COP position was a significant predictor of the knee extensor moment contribution (R² = 0.168, P = 0.030). Multivariate analysis showed that the ankle dorsiflexion angle (ΔR² = 0.561, β = 0.842) and AP-COP position (ΔR² = 0.296, β =  − 0.499) predicted the knee extensor moment contribution (model R² = 0.857, P < 0.001). Additionally, the combination of trunk flexion (ΔR² = 0.429, β =  − 0.613) and AP-COP position (ΔR² = 0.109, β =  − 0.332) predicted the knee extensor moment contribution (model R² = 0.538, P < 0.001). The limb symmetry index of the knee extensor moment was significantly associated with that of the AP-COP position (R² = 0.493, P < 0.001) but not with that of the ankle dorsiflexion angle (P = 0.057).

Conclusions

The AP-COP position can predict the contribution of the knee extensor moment and improve the prediction when combined with ankle dorsiflexion and trunk flexion. The present findings suggest that intervention focusing on the AP-COP position in combination with ankle dorsiflexion or trunk flexion would be useful to coordinate the contribution of the knee extensor moment during double-leg squatting.

Knee Movement Characteristics of Basketball Players in Landing Tasks Before Onset of Patellar Tendinopathy: A Prospective Study

Background

Patellar tendinopathy is one of the most common injuries for basketball players. Jumping and landing movement patterns are potential risk factors for patellar tendinopathy.

Hypothesis

Male college basketball players who developed patellar tendinopathy would demonstrate greater peak vertical ground reaction force and knee flexion angular velocity, and smaller knee flexion range of motion and knee flexion angles at initial contact compared to players who did not develop the injury when performing a stop-jump task within a year prior to the onset of the injury.

Study Design

Prospective study.

Methods

Freshmen college basketball male players (n = 181) were recruited for three consecutive years and followed to the end of the third year of the study. Three-dimensional kinematic and kinetic data during a stop-jump task were collected for all participants at the beginning of each school year. Peak vertical ground reaction force, knee flexion angle at initial foot contact with the ground, range of motion for knee flexion and maximal knee flexion angular velocity during the landing phases of the stop-jump task were collected and calculated. Development of patellar tendinopathy was monitored in follow-up. Independent t-tests and Cohen's d effect sizes (ES) were used to compare movement patterns between injury and no injury groups for each school year.

Results

A total of 60 knees developed patellar tendinopathy. The injury groups had a significantly greater peak vertical ground reaction force in freshmen and junior years (P = 0.020, ES = 0.13; P = 0.046, ES = 0.17), smaller knee flexion ROM in freshmen year (P = 0.002, ES = 0.10), and greater maximum knee flexion angular velocity in freshmen and junior year (P = 0.012, ES = 0.10; P = 0.001, ES = 0.35) during the horizontal landing phase before the takeoff of the jump compared to the no injury groups. The injury groups also had a significantly smaller knee flexion angle at initial contact during vertical landing phase after the takeoff of the jump in freshmen and junior years (P = 0.001, ES = 0.36; P = 0.001; ES = 0.37) during vertical landing phase.

Conclusion

Peak vertical ground reaction force, knee flexion angle at initial foot contact, knee flexion range of motion, and maximum knee flexion angular velocity are associated with patellar tendinopathy among male college basketball players in different school years.

Effects of isometric loading intensity on patellar tendon microvascular response

Acute increases in tendon blood flow and oxygenation after stress (i.e., hyperemic response) can enhance tendon recovery. While loading intensity is a fundamental part of resistance training programs, its effects on tendon's hyperemic response are unknown. This study aimed to compare acute changes in total (total hemoglobin [THb]) and oxygenated hemoglobin (HbO₂ ) concentrations in the patellar tendon after isometric exercise at different intensities. Thirteen participants performed 8 (5 s) isometric knee extensions at 25%, 50%, and 75% maximal load (maximal voluntarily isometric contraction [MVIC]), separated by 20 min recovery, prescribed in randomized and counterbalanced order. Changes in patellar tendon THb, HbO₂ and deoxygenated hemoglobin (HHb) in response to exercise at each intensity were measured using near-infrared spectroscopy. Post-exercise, HbO₂ increased with 50% ( η p 2 $$ {\eta}_p^2 $$  = 0.305, f = 5.26, p < 0.01) and 75% ( η p 2 $$ {\eta}_p^2 $$  = 0.245, f = 4.56, p < 0.01) but not 25% ( η p 2 $$ {\eta}_p^2 $$  = 0.088, f = 1.16, p = 0.339) MVIC, while THb increased in 50% ( η p 2 $$ {\eta}_p^2 $$  = 0.305, f = 5.26, p = 0.01) but not 25% ( η p 2 $$ {\eta}_p^2 $$  = 0.067, f = 0.865, p = 0.51) or 75% ( η p 2 $$ {\eta}_p^2 $$  = 0.126, f = 1.729, p = 0.14) MVIC. Additionally, increasing load from 25% to 50% MVIC resulted in greater THb (f = 2.459, p = 0.43), HbO₂ (f = 3.389, p = 0.13) and HHb (f = 0.320, p = 0.01) post-exercise responses, but no differences were observed between 50% and 75% MVIC (THb: f = 0.748, p = 0.59; HbO₂ : f = 0.825, p = 0.54; HHb: f = 0.713, p = 0.62). Our results suggest there is a loading threshold at ~50% MVIC at which the tendon hyperemic response is fully achieved. Training above this intensity is not expected to provide any additional change to the tendon microvascular response. Therefore, moderate loading seems to be sufficient to fully elicit the patellar tendon hyperemic response that's believed to stimulate tendon healing.

Using cervical movement velocity to assist the prediction of pain and functional recovery for people with chronic mechanical neck pain

BACKGROUND

Impaired cervical kinematics particularly the movement velocity had been consistently found in people with neck pain. The recovery and potential of cervical movement velocity in assisting the prediction of recovery in individuals with chronic neck pain remained unknown. This study investigated the application of cervical movement velocity to predict the outcomes of pain intensity and functional disability for a cohort of participants with chronic mechanical pain after completion of a 12-week intervention program.

METHODS

Cervical movement velocity when performing neck motions in the anatomical planes, pain intensity and functional disability score were assessed before and after the physiotherapy program. Correlations between kinematic and clinical outcomes, and validity of applying the peak velocity values of the cervical spine measured at baseline for prediction of recovery of pain and function after the physiotherapy program were examined (n = 68).

FINDINGS

Significant improvements were found in the peak values of cervical velocity in all movement planes, pain intensity and functional disability score at post-program reassessment (p < 0.001). Significant negative correlations between peak values of cervical movement velocity and pain intensity (for specific directions, r = -0.163 to -0.191), and functional disability were found (for all directions, r = -0.158 to -0.282). Area under the Receiver Operating Characteristics curve was >0.6 for cervical extension, flexion and right rotation velocity for predicting functional recovery post-program.

INTERPRETATION

These findings suggest that cervical velocity of selected planes measured at baseline may inform the prediction of recovery of functional disability but not pain intensity in people with chronic mechanical neck pain.

High-speed stretch-shortening cycle exercises as a strategy to provide eccentric overload during resistance training

Resistance exercises eliciting eccentric overload (EO) are considered to strongly promote muscular hypertrophy and broad neuromuscular adaptations but typically require specialized equipment. The aims of these experiments were to assess whether EO is achieved during common high-speed stretch-shortening cycle (SSC) exercises (rebound bench press throw [RBPT] and squat jump [SJ]), and to test the effect of the external load on the EO achieved. Twenty-nine under 18 handball players and fifteen physically active males (24.9 ± 3.2 years) took part in the experiments. Testing consisted of a single set of 6 repetitions with light (25%-30% 1-RM), moderate (50% 1-RM), and heavy (70%-75% 1-RM) loads. Eccentric and concentric force near the zero-velocity point (50-200 ms) as well as eccentric-concentric force ratio (EO; %) were calculated. In RBPT, higher EO values were found at 50% 1-RM than 70% 1-RM in the time interval 50 ms before and after the zero-velocity point. Higher EO values were also found at 50% 1-RM than both 30% 1-RM and 70% 1-RM 100 ms before and after the zero-velocity point. For the SJ, higher EO values were found at 50% 1-RM and 75% 1-RM than 25% 1-RM 100 ms before and after the zero-velocity point. Higher EO values were found at 50% 1-RM than 25% 1-RM 200 ms before and after the zero-velocity point. However, the higher EO values in the SJ were found far from the zero-velocity point. High-speed SSC resistance training provides similar EO to other methods and thus should promote muscle hypertrophy and other neuromuscular adaptations.

The Influence of Countermovement Strategy and External Load on Amortization Forces During Jump Squats

ABSTRACT

Barker, L, Siedlik, J, and Mercer, J. The influence of countermovement strategy and external load on amortization forces during jump squats. J Strength Cond Res 35(2): 332-339, 2021-The purpose of this study was to investigate the influence of countermovement strategy on amortization forces when performing jump squats. To gather a range of deceleration demands, jump squats were performed across a range of external loads (0, 15, 30, 45, and 60% of repetition maximum [1RM]) and verbally cued countermovement depths (preferred: PREF; quarter: QTR; and full: FULL). Dual force platform ground reaction force data were collected from 12 subjects. Amortization Fz, amortization time, and countermovement depth were analyzed using a 3 × 5 (technique × load) repeated measures analysis of variance. To assess countermovement strategy and amortization Fz, correlations and regression analysis were used to assess relationships among system mass, countermovement kinetic energy and depth, and amortization Fz. Amortization Fz was greater with QTR than PREF (p < 0.05), but similar between PREF and FULL (p > 0.05), and between QTR and FULL (p > 0.05). Amortization Fz was different between 0 and 15% 1RM (p < 0.05) and between 0 and 30% 1RM (p < 0.05). All loaded conditions (15-60% 1-RM) were similar (p > 0.05). As a group, countermovement kinetic energy and system mass were significantly, but weakly, correlated (r = 0.29, p < 0.01). Regression analysis revealed amortization Fz did not change in relation to countermovement kinetic energy but did change in relation to depth. These results suggest that preferred countermovement depths were associated with lesser amortization Fz (strain energy) during maximal effort unloaded and loaded countermovement jumps. Strength and conditioning professionals selecting exercises to maximize amortization Fz should consider the jump squat with light loads (or no load) and short countermovement depths.

Comparison between velocity-specific exercise and isometric exercise on neck muscle functions and performance: a randomised clinical trial

Background

Evidence has shown that velocity-specific exercise results in additional benefits for peripheral joint muscles by promoting their functions, however, its effects on spinal muscles are yet to be investigated. This study aimed to examine the feasibility and effects of velocity-specific exercise compared to isometric exercise on cervical muscle functions and performance in healthy individuals.

Methods

Thirty healthy adults were randomised to practise either the velocity-specific exercise (VSE, n = 15) or isometric exercise (IE, n = 15) for 6 weeks. Functions and performance of the cervical extensors and flexors were assessed pre- and post-program, by analyzing the peak torque and electromyography during the isokinetic testing, and cross-sectional area of the deep cervical muscles at rest. The self-reported level of difficulty and post-exercise soreness during the exercise were recorded to evaluate the feasibility and safety of the two exercise programs.

Results

Both VSE and IE exercises resulted in significant improvement of the muscle functions and performance while there were no between-group differences at reassessment of the (a) cross-sectional area of longus colli and semispinalis capitis; (b) EMG amplitude in sternocleidomastoid and cervical erector spinae, and (c) peak torque values. Further analysis revealed that degree of correlation between extension torque and EMG amplitude of cervical erector spinae increased in both groups. However, significant correlation was found only in VSE group post-program. There were no significant differences for the level of difficulty and post-exercise soreness found between two groups.

Conclusions

Both velocity-specific and isometric exercises significantly promoted cervical muscle functions and performance. The present study confirms that velocity-specific exercise can be practised safely and it also contributes to a greater enhancement in neuromuscular efficiency of the cervical extensors. These findings indicate that the velocity-specific exercise can be considered as a safe alternative for training of the cervical muscles. Further study is recommended to examine its benefit and application for promoting the muscle functions and recovery in symptomatic individuals.

Muscle activation varies between high-bar and low-bar back squat

Background

Differences in the muscular activity between the high-bar back squat (HBBS) and the low-bar back squat (LBBS) on the same representative group of experienced powerlifters are still scarcely investigated. The main purpose of the study was to compare the normalized bioelectrical activity and maximal angles within single homogeneous group between the HBBS and LBBS for 60% one repetition maximum (1RM), 65% 1RM and 70% 1RM.

Methods

Twelve healthy men (age 24.3  ± 2.8 years, height 178.8  ± 5.6 cm, body mass 88.3  ± 11.5 kg), experienced in powerlifting performed HBBS and LBBS with comparable external loads equal 60% 1RM, 65% 1RM, and 70% 1RM. Electromyography (EMG) signals of muscle groups were synchronously recorded alongside kinematic data (joints angle) by means of a motion capture system.

Results

EMG activity during eccentric phase of squat motion were significantly higher during LBBS than in HBBS for all selected muscles (60% 1RM and 65% 1RM) (p < 0.05). All examined muscles were more activated during concentric phase of the squat cycle (p < 0.05). In the concentric phase, significant differences between the loads were generally not observed between just 5% 1RM change in load level for LBBS.

Conclusions

Our results confirmed significant differences in muscles activation between both squat techniques. Muscle activity during eccentric phase of squat motion were significantly higher during LBBS than HBBS. The differences are crucial for posterior muscle chain during eccentric phase of squat cycle.

The Influence of External Load on Quadriceps Muscle and Tendon Dynamics during Jumping

Tendons possess both viscous (rate-dependent) and elastic (rate-independent) properties that determine tendon function. During high-speed movements external loading increases both the magnitude (FT) and rate (RFDT) of tendon loading.

PURPOSE

The influence of external loading on muscle and tendon dynamics during maximal vertical jumping was explored.

METHODS

Ten resistance-trained men performed parallel-depth, countermovement vertical jumps with and without additional load (0%, 30%, 60%, and 90% of maximum squat lift strength), while joint kinetics and kinematics, quadriceps tendon length (LT) and patellar tendon FT and RFDT were estimated using integrated ultrasound, motion analysis and force platform data and muscle tendon modelling.

RESULTS

Estimated FT and RFDT, but not peak LT, increased with external loading. Temporal comparisons between 0% and 90% loads revealed that FT was greater with 90% loading throughout the majority of the movement (11%-81% and 87%-95% movement duration). However, RFDT was greater with 90% load only during the early movement initiation phase (8%-15% movement duration) but was greater in the 0% load condition later in the eccentric phase (27%-38% movement duration). LT was longer during the early movement (12%-23% movement duration) but shorter in the late eccentric and early concentric phases (48%-55% movement duration) with 90% load.

DISCUSSION

External loading positively influenced peak FT and RFDT but tendon strain appeared unaffected, suggesting no additive effect of external loading on patellar tendon lengthening during human jumping. Temporal analysis revealed that external loading resulted in a large initial RFDT that may have caused dynamic stiffening of the tendon and attenuated tendon strain throughout the movement. These results suggest that external loading influences tendon lengthening in both a load- and movement-dependent manner.