Isometric Leg Press Research Articles

Are training velocity and movement pattern important determinants of muscular rate of force development enhancement?

Marshall et al. (2011) recently published the results of a comprehensive strength training study investigating the effect of the number of sets used in each training session on muscle function, hypertrophy and activation [assessed by electromyography (EMG)] in men with previous weight training experience [mean squat lift load = 159.9 kg (1.9 9 body mass)]. Squat lift training was performed at 80% of 1 RM to exhaustion twice weekly for 6 weeks, then a combination of heavier (4–12 RM) and lighter, explosive (e.g. jump squat) exercises were performed for 4 weeks. The results were very interesting, revealing that the performance of eight sets of exercises was superior to one and four sets for muscle strength improvement in their cohort. One intriguing result was that the rate of force development (RFD), measured during an isometric knee extension test, did not improve with training despite there being a small increase in the rate of muscle activation (measured as the rate of integrated EMG increase) in addition to the substantial (11.7–22.8%) increase in strength. On their own, each of these adaptations could have been expected to result in an increase in RFD (Aagaard et al. 2002). From this, it could be concluded that the preponderance of slowspeed dynamic exercises was not appropriate to improve RFD, or that the use of an isometric test was inappropriate. These opinions make sense given our understanding of the specificity of adaptations to strength training. However, the question should be asked: does the published research support these assertions? Numerous studies have reported significant enhancements in RFD measured in the isometric knee extension test after traditional, explosive or isometric strength training of the lower extremity (e.g. Aagaard et al. 2002; Blazevich et al. 2009; Blazevich et al. 2008; Del Balso and Cafarelli 2007; Hakkinen et al. 2003; Hakkinen et al. 2001a, b; Narici et al. 1996; Reeves et al. 2003; Suetta et al. 2004; Vila-Cha et al. 2010). In each of these studies, some portion of test-specific training was performed as part of the program. That is, the knee extension training was performed in training, so there was at least some similarity (specificity) between the testing and training tasks with respect to body position. The same result is seen when training is done in other muscle groups, including the trapezius (Andersen et al. 2009), elbow flexors (Barry et al. 2005; Gabriel et al. 2001), plantarflexors (Holtermann et al. 2007) and dorsiflexors (Geertsen et al. 2008), or when a multi-joint isometric leg press test is used to assess RFD after a period of dynamic leg press training (Hoff et al. 2007; Husby et al. 2009; Mosti et al. 2011; Wang et al. 2010). Of the studies cited here, the mean improvement in absolute RFD was 42.6% (mean of all published results), which, when the results are expressed as the sample size-weighted mean, equates to a 4.4% increase per week. Interestingly, there appears to be no clear evidence that there is a requirement for fast force production during the training, with increases of only 8.0% at 0.4% per week when some form of explosive training was performed compared to 31.3% at 1.3% per week when slower strength training was performed. In fact, the evidence more clearly supports the reverse hypothesis, and it is rarely seen that strength training is not associated with an increase in RFD measured isometrically (Hakkinen et al. 1998; Sleivert et al. 1995). Thus, the overwhelming Communicated by Susan A. Ward.

Enhanced Myofiber Recruitment During Exhaustive Squatting Performed as Whole-Body Vibration Exercise

The purpose of the study was to test the hypothesis that myofiber recruitment is enhanced when whole-body vibration (WBV) is added to squat training. In a randomized cross-over design, 14 recreationally active men were subjected to 2 sessions consisting of 5 sets of 10 squats with external load, performed either on a vibration platform (whole-body vibration squatting [WBVS]) or conventionally without WBV (CON). Electromyographic (EMG) activity of the right vastus lateralis muscle was continuously recorded during WBVS and CON. The integrated EMG values were normalized to the EMG activity recorded during measurement of the maximal voluntary contraction force (MVC) on an isometric leg press at the beginning of each training session. Capillary lactate concentration was determined before and repeatedly after the squatting exercise. Overall mean normalized and integrated EMG (nIEMG) activity during WBVS (62 ± 4% MVC) was significantly (p < 0.001) higher compared with CON (47 ± 2% MVC). There was a tendency for nIEMG to increase during the 5 sets of 10 squats performed as WBVS (p = 0.089), whereas there was a significant (p < 0.001) decrease in nIEMG during CON. Whole-body vibration squatting induced a significantly (p < 0.001) larger increase in capillary lactate than CON (3.03 ± 0.32 vs. 1.60 ± 0.30 mmol · L(-1), p < 0.001). The increased myoelectric activity and the enhanced exercise-induced increase in capillary lactate concentration during WBVS provide evidence for augmented recruitment of muscle tissue when WBV is added to exhaustive squatting exercise.

Neuromuscular and Hormonal Responses to Constant and Variable Resistance Loadings

The purpose of this study was to investigate the acute effects of constant and variable resistance exercise on neuromuscular and endocrine responses during maximal strength and hypertrophic loadings. Thirteen young men (age = 28.4 ± 3.7 yr) took part in four loadings (maximal strength and hypertrophic loadings using both constant and variable resistance) in a counterbalanced order. Maximal strength loadings consisted of 15 sets of one repetition at 100% one-repetition maximum, and hypertrophic loadings consisted of five sets of 10 repetitions (initial load of 80% one-repetition maximum). Preloading, immediately postloading, 15 min postloading, and 30 min postloading tests consisted of maximal bilateral isometric leg press, venous blood samples (analyzed for total testosterone, growth hormone, and cortisol), and fingertip blood lactate samples. Concentric force and vastus lateralis, vastus medialis, rectus femoris, and biceps femoris EMG was recorded throughout each loading protocol and analyzed over 20° segments. Force and quadriceps EMG was greater from 120° to 180° knee angle (P < 0.05) during variable resistance hypertrophic loadings. Larger increases in concentric quadriceps muscle activation and slower recovery in isometric force and muscle activation were observed during variable resistance hypertrophic loadings. Preloading to postloading serum total testosterone, growth hormone, and cortisol concentration increased during variable resistance hypertrophic loading, whereas during constant resistance loadings, only growth hormone increased (P = 0.051). During 30 min postloading, growth hormone and cortisol concentrations remained elevated after both hypertrophic loadings. A greater level of neuromuscular fatigue and larger responses in serum hormone concentrations occurred after hypertrophic variable resistance loading. These findings indicate greater fatigability during variable resistance loading and that this fatigability influences acute hormonal responses.

Seventy-year-old habitual volleyball players have larger tibial cross-sectional area and may be differentiated from their age-matched peers by the osteogenic index in dynamic performance

The osteogenicity of a given exercise may be estimated by calculating an osteogenic index (OI) consisting of magnitude and rate of strain. Volleyball involves repetitive jumping and requires high power output and thus may be expected to be beneficial to bone and performance. The purpose of the present study was to examine if habitual volleyball playing is reflected in OI. Ten elderly habitual volleyball players [age 69.9 (SD 4.4) years] and ten matched controls volunteered [age 69.7 (4.2) years] as subjects. Distal tibia (d), tibial mid-shaft (50) and femoral neck (FN) bone characteristics were measured using pQCT and DXA. To estimate skeletal rigidity, cross-sectional area (ToA(50)), and compressive (BSI(d)) and bending strength indices (SSImax(50)) were calculated. Maximal performance was assessed with eccentric ankle plantar flexion, isometric leg press and countermovement jump (CMJ). A fast Fourier transform (FFT) was calculated from the acceleration of the center of mass during the CMJ. Maximal acceleration (MAG) and mean magnitude frequency (MMF) were selected to represent the constituents of OI. OI was calculated as the sum of the products of magnitudes and corresponding frequencies. Volleyball players had 7% larger ToA(50) and 37% higher power in CMJ, 15% higher MAG and 36% higher OI (P <or= 0.047) than the matched controls. No difference was observed in leg press, plantar flexion or the MMF (P >or= 0.646). In conclusion, habitual volleyball players may be differentiated from their matched peers by their dynamic jumping performance, and the differences are reflected in the magnitude but not rate of loading.

Exercise, Body Composition, and Functional Ability: A Randomized Controlled Trial

In women, age and the menopausal transition contribute to an increase of body fat and a reduction of lean body mass associated with functional decline, affecting independent living. Sarcopenia and adiposity in the elderly has been associated with increased mortality and functional decline affecting independent living. This study was conducted to determine the effect of a multipurpose exercise program on the body composition and functional ability of elderly women living in a community. An 18-month single-blinded RCT comparing participants in an exercise program with an active control group was conducted from May 2005 through December 2007. Analyses were conducted from January 2008 to July 2008. Two hundred forty-six women (aged 69.1+/-4.0 years) living independently in the area of Erlangen-Nürnberg (Germany) participated in the study. Subjects (n=123) performed a multipurpose exercise program with special emphasis on exercise intensity but with low-level requirements for training facilities and materials. The 123 women in the control group focused primarily on well-being. Body composition was assessed by dual-energy x-ray absorptiometry. Further, strength was evaluated using isometric techniques for the back and legs. Aerobic fitness was determined from a progressive-intensity treadmill test. After 18 months, significant effects in favor of the exercise program for body composition were increases in appendicular skeletal muscle mass and lean body mass along with reductions in abdominal fat and total body fat. Significant performance effects also favored the exercise program and included enhanced isometric maximum trunk-extensor and leg press strength, leg press power, timed up-and-go test, and aerobic fitness. A high-intensity multipurpose exercise program produced significant improvements in body composition and functional ability in a cohort of elderly women living in a community.

Impaired leg extensor strength in individuals with Parkinson disease and relatedness to functional mobility

Previous investigations have demonstrated leg strength deficits in persons with Parkinson's disease (PD) as compared to neurologically-normal adults. However, the exact mode of contraction by which strength is assessed may determine how closely such deficits are related to functional performance. The purpose of this study was to better understand the relationship of strength and functional mobility in persons with PD ( n = 17, mean H&Y stage = 2.0) via comparison to a group of similar age healthy controls ( n = 10) using a multi-joint isometric test of strength and various measures of functional mobility. Tests included isometric leg press maximum force relative to body mass, the Activities-specific Balance Confidence scale (ABC), postural sway under various unilateral stance and visual conditions, and the timed up and go (TUG). Relative force ( p = 0.044) and ABC questionnaire mean scores ( p < 0.001), showed controls performing better than PD subjects. The control group performed better than the PD group for length of path of the center of pressure except in the eyes closed positions ( p < 0.05 for all). TUG time ( p = 0.052) was not significantly different between the PD group and healthy controls. Leg press maximum force relative to body mass was however significantly correlated with TUG time ( r = −0.68, p = 0.003) in persons with PD. There were no gender differences for any variables. These results suggest that some balance and functional mobility task performances are more worse for persons with mild-to-moderate PD than for neurologically-normal age-matched controls, which may be influenced by lessened lower extremity multi-joint strength. Strength training of the lower extremity utilizing such multi-joint actions may be beneficial for this population.

Using Maximal Isometric Force To Determine The Optimal Load For Measuring Dynamic Muscle Power

Maximal power output occurs when subjects perform ballistic exercises using loads of ~30-50% of one-repetition maximum (1-RM). However, performing 1-RM testing prior to power measurement requires considerable time, especially when testing involves multiple exercises. Maximal isometric force (MIF), which requires substantially less time to measure than 1-RM, might be an acceptable alternative for determining the optimal load for power testing. PURPOSE: To determine the optimal load based on MIF for maximizing dynamic power output during leg press and bench press exercises. METHODS: Twenty healthy volunteers (12 men and 8 women; mean +/- SD age: 31+/-6 y; body mass: 72 +/- 15 kg) performed isometric leg press and bench press movements, during which MIF was measured using force plates. Subsequently, subjects performed ballistic leg press and bench press exercises using loads corresponding to 20%, 30%, 40%, 50%, and 60% of MIF presented in randomized order. Maximal instantaneous power was calculated during the ballistic exercise tests using force plates and position transducers. Repeated-measures ANOVA and Fisher LSD post hoc tests were used to determine the load(s) that elicited maximal power output. RESULTS: For the leg press power test, six subjects were unable to be tested at 20% and 30% MIF because these loads were less than the lightest possible load (i.e., the weight of the unloaded leg press sled assembly [31.4 kg]). For the bench press power test, five subjects were unable to be tested at 20% MIF because these loads were less than the weight of the unloaded aluminum bar (i.e., 11.4 kg). Therefore, these loads were excluded from analysis. A trend (p = 0.07) for a main effect of load existed for the leg press exercise, indicating that the 40% MIF load tended to elicit greater power output than the 60% MIF load (effect size = 0.38). A significant (p . 0.05) main effect of load existed for the bench press exercise; post hoc analysis indicated that the effect of load on power output was: 30% > 40% > 50% = 60%. CONCLUSION: Loads of 40% and 30% of MIF elicit maximal power output during dynamic leg presses and bench presses, respectively. These findings are similar to those obtained when loading is based on 1-RM.

Effects of knee angle on lower extremity extension force and activation time characteristics of selected thigh muscles

The aim of the present study was to examine the effect of knee joint angles on maximal voluntary contraction (MVC) of leg extensor and electromyographic (EMG) activities of rectus femoris (RF), vastus medialis (VM), and biceps femoris (BF) during a maximal isometric leg press task. Eighteen males, aged 18-23, performed maximum bilateral voluntary isometric contractions at five knee joint angles (90 ◦ ,8 0 ◦ ,7 0 ◦ ,6 0 ◦ , and 50 ◦ ;0 ◦ = full extension). The MVC of leg extensors, the force exerted during the first 100 ms of the contraction (F100), the time achieved the MVC, and the average integrated EMG activities (AEMG) of RF, VM, and BF were measured at five knee joint angles. MVC was significantly higher ( p< 0.05 )a t 60 ◦ in comparison to the other knee joint angles, whereas AEMGs of RF and VM were significantly lower ( p< 0.05) at more extended position (50 ◦ ) than at more flexed positions (90 ◦ ,8 0 ◦ , and 70 ◦ ). AEMG of BF did not present significant changes among the five different knee joint angles. These findings suggest that MVC of leg extensor are considerably influenced by the mechanical force-length properties of skeletal muscle. The reduced activation of RF at more extended knee positions indicates its multiple function along a closed chain multi-joint task. On contrary, the similar activation of biceps femoris muscle at all five knee joint angles indicates its importance for the knee joint stability.

A Vertical Jump Force Test for Assessing Bilateral Strength Asymmetry in Athletes

To establish the validity and reliability of a new vertical jump force test (VJFT) for the assessment of bilateral strength asymmetry in a total of 451 athletes. The VJFT consists of countermovement jumps with both legs simultaneously: one on a single force platform, the other on a leveled wooden platform. Jumps with the right or the left leg on the force platform were alternated. Bilateral strength asymmetry was calculated as [(stronger leg - weaker leg)/stronger leg] x 100. A positive sign indicates a stronger right leg; a negative sign indicates a stronger left leg. Studies 1 (N = 59) and 2 (N = 41) examined the correlation between the VJFT and other tests of lower-limb bilateral strength asymmetry in male athletes. In study 3, VJFT reliability was assessed in 60 male athletes. In study 4, the effect of rehabilitation on bilateral strength asymmetry was examined in seven male and female athletes 8-12 wk after unilateral knee surgery. In study 5, normative data were determined in 313 male soccer players. Significant correlations were found between VJFT and both the isokinetic leg extension test (r = 0.48; 95% confidence interval, 0.26-0.66) and the isometric leg press test (r = 0.83; 0.70-0.91). VJFT test-retest intraclass correlation coefficient was 0.91 (0.85-0.94), and typical error was 2.4%. The change in mean [-0.40% (-1.25 to 0.46%)] was not substantial. Rehabilitation decreased bilateral strength asymmetry (mean +/- SD) of the athletes recovering from unilateral knee surgery from 23 +/- 3 to 10 +/- 4% (P < 0.01). The range of normal bilateral strength asymmetry (2.5th to 97.5th percentiles) was -15 to 15%. The assessment of bilateral strength asymmetry with the VJFT is valid and reliable, and it may be useful in sports medicine.

Effects of Power Training on Mechanical Muscle Output in Old and Very Old Elderly Women

Decline in explosive force (i.e. contractile rate of force development RFD) and mechanical muscle power with aging has been reported to correlate with reduced ability to maintain postural control and balance recovery after tripping and to predict falls in community-dwelling old adults. It was therefore recently suggested to develop strength training programmes aimed at maximising maximal muscle power and RFD. Different training protocols have been implemented with older people but no study has been designed as power training with heavy loading (75-80% 1RM) for very old individuals. PURPOSE: To evaluate the effect of low frequency (twice a week), 12-weeks power training with heavy-loading (75-80 % of 1RM) using fast-to-explosive execution of the movements on maximal voluntary contraction (MVC), explosive force characteristics (RFD and impulse) and mechanical muscle power during multi-joint motor tasks in two age-groups of community-dwelling elderly women (TG60, TG80, age-groups 60 and 80, respectively). METHODS: Elderly women from two age-groups, 60 (62.7 2.2 years, n=40) and 80 (81.8 2.7 years, n=25) were randomized (matched) into two training and two control groups (TG60, n=20; TG80, n=12) (CG 60, n=20; CG80, n=13). MVC, RFD, normalized RFD (RFD/MVC) and impulse (during 5 time intervals from onset of contraction separated by 100ms) were obtained during a maximal multi-joint isometric leg press. Mechanical muscle power was assessed in a countermovement jump (CMJ) as jump height, (JH), peak power (Ppeak), velocity and force at Ppeak (Vppeak, Fppeak, respectively). RESULTS: RFD, relative RFD, impulse, MVC, Ppeak, JH, and Vppeak increased with training (between 5 and 50%) in both age-groups whereas no changes occurred in the CG. The gains in RFD, impulse and MVC for TG 80 were of such a magnitude that the difference observed pre intervention with the age-group 60 was abolished after training. CONCLUSION: The present findings indicate that power training with heavy loading is highly effective in inducing adaptive changes in maximal and explosive mechanical muscle output in old and very old healthy women even in the 8th decade of life. Importantly, this training type seems safe and suitable in healthy older adults.

Effects of Multi-Joint Angle Changes on EMG Activity and Force of Lower Extremity Muscles during Maximum Isometric Leg Press Exercises

The objectives of this study were to identify the position where optimal leg muscle force occurs and to analyze the lower extremity muscle activity by comparing different hip and knee joint angle positions using a newly developed closed kinetic chain (CKC) leg press exercise device. Muscle force and electromyogram (EMG) measurements during maximum voluntary isometric leg presses (MVC-CKC) were performed on 6 healthy women in 6 different knee flexion angles (15°, 30°, 45°, 60°, 75°, 90°) and 2 different postures (supine and trunk upright posture). Results showed that the muscle force of MVC-CKC reached its peak at 60° knee flexion angle in both postures. Significant knee angle-dependent differences in EMG activity for both rectus femoris and gastrocnemius muscles were observed, while posture-dependent differences in EMG were found in biceps femoris. These particular joint-dependent EMG activities may be explained by the architectural characteristics of bi-articular muscles and muscle length-tension relationship theory. Co-activation of an antagonist muscle may appear with activation of the gastrocnemius muscle when the knee approaches full extension. Consequently, measurement of isometric CKC leg extension muscle force at 60° knee flexion angle in the trunk upright posture seems to be the optimal position.

Explosive-type Strength Training in the Elderly

The age-related decline in muscle power and explosive force capacity (i.e. contractile rate of force development RFD) is as stronger predictor for incidence of falling, motor impairment, self-reported functional status and balance capability in community-dwelling old adults than maximal muscle strength per se. It was therefore recently suggested to develop strength training programmes aimed at maximising maximal muscle power and RFD by implementing explosive concentric movements with training loads of 40–60% of 1RM. However, older individuals often perform weight-bearing motor tasks close to their maximum capability (i.e. 1RM) and above especially during unexpected tasks such as reversing an impending fall. PURPOSE: To investigate the effect of 12-week, twice a week, heavy-resistance strength training (75–80 % of 1RM) with fast-to-explosive execution of the movements on maximal voluntary contraction (MVC), explosive force characteristics (RFD and impulse), muscle power and functional performances in two age-groups of community-dwelling elderly women (TG60, TG80, age-groups 60 and 80, respectively). METHODS: Elderly women from two age-groups, 60 (62.7 2.2 years, n=40) and 80 (81.8 2.7 years, n=25) were randomized (matched) into two training and two control groups (TG60, n=20; TG80, n=12) (CG 60, n=20; CG80, n=13). MVC, RFD and impulse were obtained during a maximal isometric unilateral leg press manuevre. Mechanical performance was assessed as jump height, (JH) and peak power (Ppeak) in a standardized countermovement jump (CMJ) and as mean power (Prigmean). in the Nottingham single-legged power rig. Functional motor performances were i) five-repeated chair rise, ii) 10-m walking test at self selected and maximal speed, and iii) Physical Performance Test (PPT). RESULTS: RFD, impulse, MVC, P peak', JH and Prigmean increased with training in both age-groups. The gains in RFD (50.5%), impulse (41.9%) and MVC (28.1%) for TG 80 were of such a magnitude that the difference observed pre intervention with the age-group 60 was abolished after training. Chair-rise and PPT improved in TG80 and only chair rise in TG60, whereas no improvements occurred in self-selected and maximal 10-meter gait speed. CONCLUSIONS: The present findings indicate that heavy-resistance strength training performed with explosive movement characteristics is highly effective in inducing adaptive neuromuscular changes in selected physiological variables and functional performances commonly associated with risk of falls and disability in aged individuals. This training modality seems to be safe and suitable for healthy women even in the 8th decade of life.

Effects of combined strength and kick coordination training on soccer kick biomechanics in amateur players

The aim of this study was to examine the effect of a soccer (strength and technique) training program on kinematics and electromyographic (EMG) muscle activity during a instep kick. Ten amateur soccer players (aged 19.9+/-0.4 years, body mass 74.8+/-9.1 kg, height 177.4+/-6.7 cm) constituted the experimental group (EG) whereas 10 players (age 21.6+/-1.3 years, weight 71.5+/-6.7 kg, height 175.2+/-3.4 cm) served as controls (CG). The EG followed a 10-week soccer-specific training program combining strength and technique exercises. All participants performed an instep soccer kick using a two-step approach while three-dimensional data and EMG from six muscles of swinging and support legs were recorded prior to and after training. Maximum isometric leg press strength, 10-m sprint performance and maximum speed performance on a bicycle ergometer were also measured. Analysis of variance designs with repeated measures showed that the EG improved significantly (P<0.05) maximum ball speed, the linear velocity of the foot, ankle and angular velocity of all joints during the final phase of the kick. Training had insignificant effects on EMG values, apart from an increase in the averaged EMG of the vastus medialis whereas maximum isometric strength and sprint times significantly improved after training (P<0.05). The present results suggest that the application of the training programs using soccer-specific strength exercises would be particularly effective in improving of soccer kick performance.

Influences of Repetitive Drop Jump and Isometric Leg Press Exercises on Tendon Properties in Knee Extensors

The present study aimed to investigate the effects of repetitive drop jumps (DJ) and isometric leg presses (LP) on the tendon properties in knee extensors. Before and after each endurance test, the elongation (L) of the tendon and aponeurosis of the vastus lateralis muscle was measured directly by ultrasonography while the subjects performed ramp isometric knee extensions up to maximum voluntary isometric contraction. Eight men performed 100 repetitions of the DJ and 50 repetitions of the LP for 10 seconds with 10 seconds relaxation. In the DJ, there were no significant differences in L values at any force production levels before and after each endurance test. In LP, however, the L values above 500 N were significantly greater after the endurance test than before. These results suggest that the tendon properties in knee extensors change to become more compliant after the repeated longer-duration contractions, but not after repeated ballistic exercises.

Effect of tibia rotation on the electromyographical activity of the vastus medialis oblique and vastus lateralis longus muscles during isometric leg press

Objectives: To evaluate the electrical activity of the vastus medialis obliquus (VMO) and vastus lateralis longus (VLL) with the tibia in neutral, medial and lateral rotation on the horizontal leg press. Design: Repeated measures analysis of the effects of tibia rotation on VMO and VLL activity. Setting: Evaluation and intervention in orthopaedics and traumatology laboratory. Participants: Fifteen healthy participants, no previous musculoskeletal damage of the lower limb. Main outcome measures: Electrical activity (Root Mean Square) of the VMO and VLL was measured during submaximal isometric contractions (SIC) with the knee at 90° of flexion. The effect of tibia rotation in electrical activity of the VMO and VLL was measured. Results: VLL activity was significantly higher than VMO activity with the tibia in medial rotation ( p=0.03). Tibia rotation did not influence the activity of the VMO muscle ( p=0.26). VLL activity was significantly higher with medial than neutral tibia rotation ( p=0.005). Conclusions: The results suggest that tibia rotation does not strengthen selectively the VMO muscle during isometric leg press at 90° knee flexion.

IMPACT OF SUBJECTS?? INITIAL CHARACTERISTICS AND EXERCISE TYPE INTERVENTION ON BMD CHANGES IN POSTMENOPAUSAL WOMEN

Despite a reduced skeletal response to mechanical stimulus, older women present a greater skeletal response variability when compared with young women. PURPOSE This study was designed to determine the influence of subject's individual characteristics and exercise type on bone mineral density change (ΔBMD) in the femoral neck and lumbar spine. METHODS Subjects were 36 women, 53–78 yrs, at least 1 yr postmenopausal, not taking any medication affecting bone. Subjects were randomly assigned to a hydro-gymnastics (HG, n = 20) and step aerobics (SG, n = 16) groups during 18 months, 2 or 3 sessions/wk, respectively. Ground reaction forces of SG program were between 1.6–1.7 of body weight. Assessment of BMD, fat mass and fat-free mass was performed with DXA. Upper and lower body muscle strength was evaluated with a hand dynamometer and an isometric leg press test. Calcium and magnesium on the plasma were measured by atomic absorption spectrophotometry. Calcium and magnesium intake were evaluated with 3-d food records. Stepwise regression was used to analyze the contribution of initial subjects characteristics on ΔBMD. Predictors selected by regression were then used as covariates to analyze group differences on ΔBMD. RESULTS Age explained 16.4% of the ΔBMD variance on femoral neck (β = 0.405, p = 0.021). Initial lumbar spine BMD (β = −0.367, p = 0.028) and fat-free mass (β = −0.351, p = 0.035) explained 27.3% of the ΔBMD variance on spine. Using these predictors as covariates, ANCOVA showed ΔBMD group differences on spine (HG 2.8 ± 0.6% vs. SG 0.4 ± 0.8%, p < 0.001) but not on femoral neck (HG −0.7 ± 0.9% vs. SG – 0.6 ± 1.0%, p = 0.801). CONCLUSION The efficacy magnitude of a specific exercise intervention for bone seems to be dependent of some subject characteristics. After adjusting for other predictors, the HG program induced a higher ΔBMD on lumbar spine of postmenopausal women while femoral neck ΔBMD was not impacted by either program. Supported by the Portuguese Foundation for Science (Sapiens 358007/99)

Reliability of Maximum Isometric Force-Time Parameters during a Leg Press Test in Pubertal Basketball Players

Fifteen young basketball players (aged 14.4 – 0.5 yrs) underwent two identical testing sessions spaced one week apart, to determine the reliability of maximum isometric force and force-time parameters during a maximal bilateral isometric leg press effort. The maximal isometric force (MIF), the ratio of maximal force to time (TMIF) to attain maximal force (ARMIF), starting strength (F50), and on a relative scale the time taken to increase the force from 10% to 30%, 60%, and 90% of maximal force were calculated. High intraclass correlation coefficients (ICC) were found for MIF (0.96), ARMIF (0.85), and F50 (0.90). On the relative scale, the ICCs for the times to produce 30%, 60%, and 90% of maximum force were 0.94, 0.95, 0.95, respectively. The present results indicate that maximum isometric force and the force-time parameters during a bilateral leg press can be measured reliably in pubertal basketball players.

Electromyographic fatigue characteristics of the quadriceps in patellofemoral pain syndrome

This study compared the fatigue characteristics of the vastus medialis oblique (VMO), vastus lateralis (VL) and rectus femoris (RF) muscles. Ten healthy subjects with 10 patients with patellofemoral pain syndrome (PFPS) performed an isometric leg press for 60 seconds at 60% MVIC with data collected using surface EMG. The power spectrum was analyzed and the extracted median frequency normalised to calculate a linear regression slope for each muscle. A repeated measures ANOVA revealed no significant differences, neither between the groups (P=0.592) nor the muscles (P=0.434). However, the slopes for the VMO and VL were different between the two groups with similar slopes for the RF. There was much larger variability of MF values in the PFPS group. The VMO:VL ratio calculated from these slopes for the healthy subjects was 1.17 and for the PFPS group was 1.78. These results may indicate unusual features in the fatigue indices of the quadriceps in PFPS.

The effect of knee angle on the external validity of isometric measures of lower body neuromuscular function

The aim of this study was to evaluate the effect of varying knee angle (120° and 90°) on the external validity of an isometric leg press test with reference to vertical jump performance. Isometric peak force (PF 120 and PF 90 ), rate of force development (RFD 120 and RFD 90 ), and maximum height reached with a squat jump and counter-movement jump were measured in 14 males. Although RFD 120 was significantly correlated with squat jump and counter-movement jump performance ( r = 0.71 and 0.69), and the correlations with PF 120 approached statistical significance ( r = 0.53 and 0.50), neither PF 90 nor RFD 90 was significantly related to vertical jump performance. Furthermore, although both RFD 120 and PF 120 were significantly different between the best five and the worst five jumpers, RFD 90 and PF 90 did not differentiate between individuals' vertical jump performance. We conclude that the choice of joint angle affects the external validity of isometric strength testing. Based on our results, we recommend accurate control of biomechanical specificity and assessment at different angles to find the position at which isometric strength testing is most comfortable.