Effect of countermovement on power–force–velocity profile

Purpose

To study the effect of a countermovement on the lower limb force–velocity (F–v) mechanical profile and to experimentally test the influence of F–v mechanical profile on countermovement jump (CMJ) performance, independently from the effect of maximal power output (P _max).

Methods

Fifty-four high-level sprinters and jumpers performed vertical maximal CMJ and squat jump (SJ) against five to eight additional loads ranging from 17 to 87 kg. Vertical ground reaction force data were recorded (1,000 Hz) and used to compute center of mass vertical displacement. For each condition, mean force, velocity, and power output were determined over the entire push-off phase of the best trial, and used to determine individual linear F–v relationships and P _max. From a previously validated biomechanical model, the optimal F–v profile maximizing jumping performance was determined for each subject and used to compute the individual mechanical F–v imbalance (Fv _IMB) as the difference between actual and optimal F–v profiles.

Results

A multiple regression analysis clearly showed (r ² = 0.952, P < 0.001, SEE 0.011 m) that P _max, Fv _IMB and lower limb extension range (h _PO) explained a significant part of the interindividual differences in CMJ performance (P < 0.001) with positive regression coefficients for P _max and h _PO and a negative one for Fv _IMB.

Conclusion

Compared to SJ, F–v relationships were shifted to the right in CMJ, with higher P _max, maximal theoretical force and velocity (+35.8, 20.6 and 13.3 %, respectively). As in SJ, CMJ performance depends on Fv _IMB, independently from the effect of P _max, with the existence of an individual optimal F–v profile (Fv _IMB having an even larger influence in CMJ).     

The force–velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force–velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. Seven subjects performed submaximal voluntary lengthening, shortening(at angular, velocities of +5, –5, +15, –15 and +30, and –30° s^–1) and isometric plantar flexor efforts against an ankle torque motor. Angle-specific (90°) measures of plantar flexor torque plus surface and intramuscular electromyography from soleus, medial gastrocnemius and tibialis anterior were made. The level of activation (30% of maximal voluntary isometric effort) was maintained by providing direct visual feedback of the soleus electromyogram to the subject. In an attempt to isolate the contribution of soleus to the resultant plantar flexion torque, activation of the synergist and antagonist muscles were minimised by: (1) flexing the knee of the test limb, thereby minimising the activation of gastrocnemius, and (2) applying an anaesthetic block to the common peroneal nerve to eliminate activation of the primary antagonist muscle, tibialis anterior and the synergist muscles, peroneus longus and peroneus brevis. Plantar flexion torque decreased significantly (P<0.05) after blocking the common peroneal nerve which was likely due to abolishing activation of the peroneal muscles which are synergists for plantar flexion. When normalised to the corresponding isometric value, the force–velocity relationship between pre- and post-block conditions was not different. In both conditions, plantar flexion torques during shortening actions were significantly less than the isometric torque and decreased at faster velocities. During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).     

Acute effects of different set configurations during a strength-oriented resistance training session on barbell velocity and the force–velocity relationship in resistance-trained males and females

Purpose

This study explored the acute effects of strength-oriented resistance training sessions performed using three different set configurations on barbell velocity and the force–velocity (F–v) relationship of upper-body muscles in men and women.

Method

Thirteen men (age: 23.8 ± 2.5 years; 6-repetition maximum [6RM] load: 73.4 ± 15.6 kg) and 13 women (age: 21.5 ± 1.4 years; 6RM load: 32.8 ± 5.2 kg) performed 24 repetitions with a 6RM load during the bench press exercise using traditional (TR: 6 sets of 4 repetitions with 3 min of rest between sets), cluster (CL: 6 sets of 4 repetitions with 15 s of intra-set rest every two repetitions and 2 min and 45 s of rest between sets) and inter-repetition rest (IRR: 1 set of 24 repetitions with 39 s of rest between repetitions) set configurations. The F–v relationship parameters [maximum force (F₀), maximum velocity (v₀) and maximum power (P_max)] were determined before and after each training session.

Results

The average training velocity did not differ between the three set configurations (p = 0.234), but the IRR set configuration generally provided higher velocities during the last repetition of each set. Significant decreases in F₀ (p = 0.001) and P_max (p = 0.024) but not in v₀ (p = 0.669) were observed after the training sessions. Comparable velocity loss was observed for men and women (− 12.1% vs. − 11.3%; p = 0.699).

Conclusions

The administration of very short intra-set rest periods does not allow for the attainment of higher velocities than traditional set configurations during strength-oriented resistance training sessions conducted with the bench press exercise when the work-to-rest ratio is equated.

     

Influence of muscle architecture on the torque and power–velocity characteristics of young and elderly men

This study investigated the contribution of muscle architecture to the differences in the torque–velocity and power–velocity relationships between older (OM n = 9, aged 69–82 years) and younger men (YM n = 15, aged 19–35 years). Plantarflexors’ (PF) maximal isometric and concentric torques were recorded at 0.87, 1.75, 2.62, 3.49 and 4.36 rad s⁻¹. Physiological cross-sectional area (PCSA) was calculated as the ratio of muscle volume (determined by magnetic resonance imaging) to muscle fascicle length (L _f, measured by ultrasonography). GM PCSA and L _f of the OM were, respectively, 14.3% (P < 0.05) and 19.3% (P < 0.05) smaller than of the YM. In the OM, GM maximum isometric torque and maximum contraction velocity (V _max), estimated from Hill’s equation were, respectively, 48.5 and 38.2% lower (P < 0.001) than in the YM. At all contraction velocities, the OM produced less torque than the YM (46.3% of YM at 0.87 rad s⁻¹ to 14.7% at 4.36 rad s⁻¹, P < 0.001). Peak power (PP) of the OM was 80% lower than that of the YM and normalisation of PP to muscle volume only reduced this difference by 10%. Normalisation of torque to PCSA reduced, but did not eliminate, differences in torque between YM and OM (9.6%) and differences in torque/PCSA increased with contraction velocity (P < 0.05). After normalisation of velocity to L _f, the difference in V _max between the OM and the YM was reduced to 15.9%. Thus, although muscle architecture contributes significantly to the differences in the torque– and power–velocity properties of OM and YM, other contractile factors, intrinsic to the muscle, seem to play a role. It is noteworthy that the deficit in PP between OM and YM is far greater than that of muscle torque, even after normalisation of PP to muscle volume. This finding likely plays an important role in the loss of mobility in old age.     

Force–velocity relationship of leg extensors obtained from loaded and unloaded vertical jumps

Purpose

Resent research has suggested that loaded multi-joint movements could reveal a linear force–velocity (F–V) relationship. The aim of the present study was to evaluate the F–V relationship both across different types of vertical jumps and across different F and V variables.

Methods

Ten healthy subjects performed maximum various vertical jumps that were either loaded or unloaded by constant external forces of up to 30 % of their body weight. Both the maximum and averaged F and V data were recorded.

Results

The observed F–V relationships proved to be strong (median correlation coefficients ranged 0.78–0.93) and quasi-linear. Their F- and V-intercepts and the calculated maximum power (P) were highly reliable (0.85 < ICC < 0.98), while their concurrent validity with respect to their directly measured values was on average moderate-to-large. The obtained F–V relationships also revealed that (1) the assessment of maximum F and P could be somewhat more reliable and valid than the assessment of maximum V, (2) natural countermovement jumps should be employed rather than the jumps performed from a fixed squat position, while (3) both maximum and averaged F and V variables could be used despite revealing markedly different regression parameters.

Conclusions

The data generally reveal a reliable, valid, strong and quasi-linear F–V relationship across variety of vertical jumps and the recorded F and V variables. Therefore, we conclude that the loaded vertical jumps could be developed into a routine method for testing the force, velocity, and power generating capacity of leg extensors.     

The generalized force–velocity relationship explains why the preferred pedaling rate of cyclists exceeds the most efficient one

The most efficient pedaling rate (lowest oxygen consumption) at a workload of 50–300 W has been reported to be in the range of 42–60 rpm. By contrast, most competitive cyclists prefer a pedaling rate of more than 90 rpm. The reason for this difference is still unknown. We assume that the high pedaling rate preferred by cyclists can be explained by the inherent properties of muscle fibers. To obtain statements which do not depend on muscles cross-section and length, we generalized Hills characteristic equations where muscle force and heat liberation are related to shortening velocity. A pedaling rate of f _max yields to maximal efficiency, whereas the higher pedaling rate f _Pmax leads to maximal power. The ratio f _Pmax/f _max between these two pedaling rates ranges from 1.7 to 2.4, and it depends on the muscles fiber-type composition. In sprints and competitions of very short duration, f _Pmax is more advantageous because energy supply is not the predominant limiting factor. The price to be paid for the most powerful pedaling rate is lower efficiency and higher energy cost. In longer exercises, economy is more important and the optimal pedaling rate shifts toward f _max. We conclude that the optimal pedaling rate, representing the fastest race performance, is not fixed but depends on race duration; it ranges between f _max and f _Pmax. Our results are not only of interest for competitive cyclists but also for investigations using cycle ergometers: maximum power might not be reached by using a pedaling rate near the most efficient one.This revised version was published online in March 2005 with corrections to the equations.     

Blood pressure response to force–velocity properties of the knee-hip extension movement

This study aimed to examine the effects of maximum static and dynamic forces during and after knee-hip extension movement on blood pressure. Blood pressure was measured with a combination of oscillometric and tonometry methods before, during, immediately after and 30 s after knee-hip extension movements performed under maximum isometric and various isotonic force conditions on the servo-controlled dynamometer. The force–velocity relation of knee-hip extension movement was linear (r ² = 0.9989), so that maximum isometric force (F _max) and unloaded velocity (V _max) were obtained by extrapolation. F _max coincided with measured maximum isometric force (F ₀) (F ₀/F _max = 1.03 ± 0.25). During isometric contraction, mean arterial pressure (MAP) increased to a larger extent and the increase was significantly higher than those during all controlled-load range of isotonic force measurements. The magnitude of MAP response during maximum isometric exercise was positively correlated with both F ₀ (r = 0.687, P < 0.01) and V _max (r = 0.586, P < 0.05). On the other hand, there was no significant correlation between F ₀ and V _max (r = 0.451, P > 0.05). It is suggested that measurements of muscular function with isotonic trials cause smaller increase in blood pressure than isometric trials do. Also, it was indicated that individuals with greater muscular strength and speed might respond with larger changes in blood pressure to strenuous muscular exercises.     

Influence of road incline and body position on power–cadence relationship in endurance cycling

In race cycling, the external power-cadence relationship at the performance level, that is sustainable for the given race distance, plays a key role. The two variables of interest from this relationship are the maximal external power output (P (max)) and the corresponding optimal cadence (C (opt)). Experimental studies and field observations of cyclists have revealed that when cycling uphill is compared to cycling on level ground, the freely chosen cadence is lower and a more upright body position seems to be advantageous. To date, no study has addressed whether P (max) or C (opt) is influenced by road incline or body position. Thus, the main aim of this study was to examine the effect of road incline (0 vs. 7%) and racing position (upright posture vs. dropped posture) on P (max) and C (opt). Eighteen experienced cyclists participated in this study. Experiment I tested the hypothesis that road incline influenced P (max) and C (opt) at the second ventilatory threshold ([Formula: see text] and [Formula: see text]). Experiment II tested the hypothesis that the racing position influenced [Formula: see text], but not [Formula: see text]. The results of experiment I showed that [Formula: see text] and [Formula: see text] were significantly lower when cycling uphill compared to cycling on level ground (P < 0.01). Experiment II revealed that [Formula: see text] was significantly greater for the upright posture than for the dropped posture (P < 0.01) and that the racing position did not affect [Formula: see text]. The main conclusions of this study were that when cycling uphill, it is reasonable to choose (1) a lower cadence and (2) a more upright body position.     

Effects of S-glutathionylation on the passive force–length relationship in skeletal muscle fibres of rats and humans

Journal of Muscle Research and Cell Motility - This study investigated the effect of S-glutathionylation on passive force in skeletal muscle fibres, to determine whether activity-related redox...     

Modeling of skeletal muscle: the influence of tendon and aponeuroses compliance on the force–length relationship

The aim of this study was to investigate the influence of changing elastic properties of tendon and aponeuroses on force production and muscle geometry. A three-dimensional, structural, continuum mechanics model of the cat medial gastrocnemius was used for this purpose. Increasing compliance in tendon and aponeuroses caused a decrease in the peak isometric force and a shift of the force–length relationship to the right of the length axis (i.e. toward greater muscle lengths). This result can be explained with the stability condition of the force–length relationship which produced a history dependence of force production that is conceptually in agreement with experimental observations.     

Influence of chronic food deprivation on structure–function relationship of juvenile rat fast muscles

In the present study, we analyze the influence of chronic undernutrition on protein expression, muscle fiber type composition, and fatigue resistance of the fast extensor digitorum longus (EDL) muscle of male juvenile rats (45 ± 3 days of life; n = 25 and 31 rats for control and undernourished groups, respectively). Using 2D gel electrophoresis and mass spectrometry, we identified in undernourished muscles 12 proteins up-regulated (8 proteins of the electron transport chain and the glycolytic pathway, 2 cross-bridge proteins, chaperone and signaling proteins that are related to the stress response). In contrast, one down-regulated protein related to the fast muscle contractile system and two other proteins with no changes in expression were used as charge controls. By means of COX and alkaline ATPase histochemical techniques and low-frequency fatigue protocols we determined that undernourished muscles showed a larger proportion (15 % increase) of Type IIa/IId fibers (oxidative-glycolytic) at the expense of Type IIb (glycolytic) fibers (15.5 % decrease) and increased fatigue resistance (55.3 %). In addition, all fiber types showed a significant reduction in their cross-sectional area (slow: 64.4 %; intermediate: 63.9 % and fast: 61.2 %). These results indicate that undernourished EDL muscles exhibit an increased expression of energy metabolic and myofibrillar proteins which are associated with the predominance of oxidative and Type IIa/IId fibers and to a higher resistance to fatigue. We propose that such alterations may act as protective and/or adaptive mechanisms that counterbalance the effect of chronic undernourishment.     

Surface electromyograms of agonist and antagonist muscles during force development of maximal isometric exercises—effects of instruction

Surface integrated electromyograms (iEMG) of agonist and antagonist muscles were studied during the rising phase of maximal isometric efforts (elbow flexion, unilateral and bilateral leg extension) to explain the difference in maximal rate of force development (MRFD) with a hard-and-fast instruction (instruction I) and a fast instruction (instruction II ). Force and EMG were simultaneously recorded in 24 athletes and iEMG were computed at MRFD and during different phases of force development (P _0–25, P _25–50, P _50–75, P _75–90 and P _90–100). A two-way ANOVA for repeated measures (muscle × instruction) showed that the value of iEMG at MRFD was significantly higher with instruction II for elbow flexion, unilateral and bilateral leg press exercises (F>4.9; P<0.04). The effect of instruction upon iEMG of the agonist muscles corresponding to the different phases of the force development was significant for elbow flexion (F=4.2;P<0.05 ) unilateral (F>6.4; P<0.02) and bilateral leg extension (F>9 and P<0.006 for soleus and vastus lateralis; but F=3.2 and P=0.08 for vastus medialis). There was a significant interaction between instruction and phase of force development (F>2.6; P<0.05 ): iEMG was significantly higher with instruction II at the beginning of force development (P _0–25) for all the muscles (except the soleus muscle during the bilateral leg exercise) but not at higher force (P _75–90 and P _90–100). The steeper force development with instruction II can be explained by the better activation of the agonist muscles at the beginning of force development. A lower co-activation of the antagonist muscles does not explain the improvement in MRFD as the iEMG of the antagonist muscles was not lower with instruction II but was proportional to the activation level of the agonist muscle. Electronic Publication     

A comparison of modelling procedures used to estimate the power–exhaustion time relationship

This study aimed to test the consistency of using the power required to elicit maximal oxygen uptake during incremental test (P _t) to demarcate the range of power intensity in the modelling of the power–exhaustion time relationship. Different mathematical procedures were tested using data from ten subjects exercising on a cycle ergometer. After the determination of P _t and the power at the ventilatory threshold, the subjects did six tests at constant power to exhaustion within 2–15 min. Estimates were obtained from a segmented model using two distinct equations of the anaerobic contribution to power below and above P _t, respectively. This model fit the overall data with a better adequacy than the simple hyperbolic model (standard error of 29.2 ± 25.2 vs. 42.3 ± 25.2 s). The power asymptotes were 225.7 ± 27.3 W from the segmented model, 226.2 ± 27.3 and 283.3 ± 20.5 W from the simple model applied to data below and above P _t, respectively. The estimates from the segmented model were strongly correlated with their analogues from the simple model applied only to data below P _t (R = 1.00 for power asymptote and curvature coefficient). They were not correlated with their analogues from the simple model applied only to data above P _t. These discrepancies between modelling procedures could arise from the method used to determine P _t and the oversimplification of the oxygen uptake kinetics. These limitations could lead the segmented model to an overestimation of the anaerobic contribution which was around 15% of total energy expended at P _t.     

Quadriceps maximal power and optimal shortening velocity in 335 men aged 23–88 years

The ability to develop adequate quadriceps muscle power may be highly predictive of subsequent disability among older persons. Rate as well as quantitative (sarcopenia) and qualitative (among other slowing of muscles) contributors to that age-related power decline are poorly known. The relationship of quadriceps maximal short-term power (P_max) and corresponding optimal shortening velocity (_opt) with age was assessed in 335 healthy men aged 23–88 years. The P_max and _opt were measured on a friction loaded non-isokinetic cycle ergometer. Anthropometric dimensions were used to estimate lean thigh volume (LTVest) and quadriceps mass. The decline in P_max across the adult life span (10.7% per decade) was greater than the usually reported decrease in maximal muscle strength. Power decreased already after the fourth decade. Both muscle mass (4.1% decline for LTVest or 3.4% for quadriceps mass per decade) and _opt (6.6% decline per decade) contributed to the decrease in power. Age contributed to the variability in P_max independently to the LTVest/quadriceps mass and _opt. The age-related decrease pattern of P_max reflects both stabilization (or even increase) of anthropometric measures (LTVest or quadriceps mass) from youth to middleage and systematic decline of _opt already from the thirties. This implicates more focus on velocity-orientated training as a means of enhancing leg power and improving functional status.