Comparison of Unilateral Squat Strength Between the Dominant and Non-Dominant Leg in Men and Women

The purpose of this study was to compare unilateral squat strength of the dominant and non-dominant leg in young adult men and women. Seventeen apparently healthy men (mean mass 90.5 ± 20.9 kg and age 21.7 ± 1.8 yrs) and 25 women (mean mass 62.2 ± 14.5 kg and age 21.9 ± 1.3 yrs) completed the study. To determine unilateral strength, the subjects completed a one repetition maximum (1RM) modified unilateral squat (MUS) on the dominant and non-dominant leg. The subjects completed the squat to a depth that attained a 90° angle at the knee. This exercise was executed by placing the top of the metatarsophalangeal area of the foot of the uninvolved leg on a support bar behind the subject to isolate the use of the lead leg. Paired samples t-test revealed no significant difference between the men’s 1RM mean strength on the dominant (107.0 ± 21.4 kg) and non-dominant (106.0 ± 21.4 kg) leg with a mean side-to-side difference (comparing the stronger to the weaker leg) of 2.8 %. Leg strength symmetry was also found between the women’s 1RM mean strength on the dominant (45.3 ± 12.5 kg) and non-dominant (45.0 ± 12.4 kg) leg with a mean side-to-side difference of 5.0 %. The data indicate that unilateral squat strength, measured in a weight bearing stance, is similar in the dominant and non-dominant leg in apparently healthy young adult men and women.

Key Points

• MUS strength was similar between the dominant and non-dominant leg in young adult men and women.
• Mean side-to-side differences (comparing the stronger to the weaker leg) resulted from higher dominant and non-dominant scores for the men and women
• The range of side-to-side differences warrants the practice of weight bearing strength assessment to identify those at risk for injury.

Key words: Closed Chain, limb symmetry, single-leg strength, unilateral assessment     

The Relationship Between Maximum Unilateral Squat Strength and Balance in Young Adult Men and Women

The purpose of this study was to determine the relationship between unilateral squat strength and measures of static balance to compare balance performance between the dominant and non-dominant leg. Seventeen apparently healthy men (mean mass 90.5 ± 20.9 kg and age 21.7 ± 1.8 yrs) and 25 women (mean mass 62.2 ± 14.5 kg and age 21.9 ± 1.3 yrs) completed the study. Weight bearing unilateral strength was measured with a 1RM modified unilateral squat on the dominant and non-dominant leg. The students completed the stork stand and wobble board tests to determine static balance on the dominant and non-dominant leg. Maximum time maintained in the stork stand position, on the ball of the foot with the uninvolved foot against the involved knee with hands on the hips, was recorded. Balance was measured with a 15 second wobble board test. No significant correlations were found between the measurements of unilateral balance and strength (r values ranged between -0.05 to 0.2) for the men and women. Time off balance was not significantly different between the subjects’ dominant (men 1.1 ± 0.4 s; women 0.3 ± 0.1 s) and non-dominant (men 0.9 ± 0.3 s; women 0.3 ± 0.1 s) leg for the wobble board. Similar results were found for the time balanced during the stork stand test on the dominant (men 26.4 ± 6.3 s; women 24.1 ± 5.6 s) and non-dominant (men 26.0 ± 5.7 s; women 21.3 ± 4.1 s) leg. The data indicate that static balance and strength is unrelated in young adult men and women and gains made in one variable after training may not be associated with a change in performance of the other variable. These results also suggest that differences in static balance performance between legs can not be determined by leg dominance. Similar research is needed to compare contralateral leg balance in populations who participate in work or sport activities requiring repetitive asymmetrical use. A better understanding of contralateral balance performance will help practitioners make evaluative decisions during the rehabilitation process.

Key Points

• 1RM unilateral squat strength is unrelated to measures of unilateral static balance in young adult men and women
• Static balance is similar between the dominant and non-dominant leg in young adult men and women
• Side-to-side differences in balance warrant assessment and training to correct imbalances prior to participation in activities that present a high risk for injury.

Key words: Single-leg strength, closed kinetic chain, unilateral balance, resistance exercise     

The Relationship Between Isometric and Dynamic Strength in College Football Players

Previous research has demonstrated the importance of both dynamic and isometric maximal strength and rate of force development (RFD) in athletic populations. The purpose of this study was to examine the relationships between measures of isometric force (PF), RFD, jump performance and strength in collegiate football athletes. The subjects in this study were twenty-two men [(mean ± SD):age 18.4 ± 0.7 years; height 1.88 ± 0.07 m; mass 107.6 ± 22.9 kg] who were Division I college football players. They were tested for PF using the isometric mid thigh pull exercise. Explosive strength was measured as RFD from the isometric force-time curve. The one repetition maximum (1RM) for the squat, bench press and power clean exercises were determined as measures of dynamic strength. The two repetition maximum (2RM) for the split jerk was also determined. Vertical jump height and broad jump was measured to provide an indication of explosive muscular power. There were strong to very strong correlations between measures of PF and 1RM (r = 0. 61 - 0.72, p < 0.05). The correlations were very strong between the power clean 1RM and squat 1RM (r = 0.90, p < 0.05). There were very strong correlations between 2RM split jerk and clean 1RM (r = 0.71, p < 0.05), squat 1RM (r = 0.71, p < 0.05), bench 1RM (r = 0.70, p < 0.05) and PF (r = 0.72, p < 0.05). There were no significant correlations with RFD. The isometric mid thigh pull test does correlate well with 1RM testing in college football players. RFD does not appear to correlate as well with other measures. The isometric mid thigh pull provides an efficient method for assessing isometric strength in athletes. This measure also provides a strong indication of dynamic performance in this population.

Key points

• In Division I college football players the isometric mid thigh pull test correlates well with 1RM testing.
• Rate of Force Development does not appear to be as closely related to dynamic and isometric strength in college football players.
• The isometric mid thigh pull provides a quick and efficient method for assessing isometric strength in athletes.

Key words: Isometric strength, American football, power     

Do Changes in Muscle Architecture Affect Post-Activation Potentiation?

The purpose of this randomized, cross-over design study was to examine the effect of three different muscle potentiation protocols on acute changes in muscle architecture and vertical jump performance. Eleven experienced, resistance trained men (25.2±3.6y) completed three potentiation squat protocols using moderate intensity (MI; 75%, 3 sets x 10 repetitions), high intensity (HI; 90%, 3 sets x 3 repetitions) and 100% (1RM; 1 set x 1repetition) of their 1RM. In addition, all participants completed a control session (CTL) in which no protocol was performed. During each testing session, muscle architecture and vertical jump testing were assessed at baseline (BL), 8min post (8P) and 20min post (20P) workout. Ultrasound measures included cross sectional area (CSA) and pennation angle (PANG) of both the rectus femoris (RF) and vastus lateralis (VL). Following each ultrasound measure, peak vertical jump power (PVJP) and mean (MVJP) power was assessed using an accelerometer. Magnitude based inferences were used to make comparisons between trials. The MI trial resulted in a likely greater increase from BL to 8P and 20P in RF-CSA and VL-CSA, while the HI trial resulted in a likely greater change from BL to 20P in both RF-CSA and VL-CSA. Meanwhile, changes in PVJP and MVJP for the MI trial was likely decreased at BL-8P and BL–20P, while the HI trial was shown to result in a likely or possible decrease compared to CTL at BL-8P and BL–20P, respectively. A likely negative relationship was observed between changes in VL-PANG and MVJP (r = -0.35; p , 0.018) at BL-8P, and between changes in PVJP and RF-CSA (r = -0.37; p , 0.014) at BL–20P. Results of this study were unable to demonstrate any potentiation response from the trials employed, however these protocols did result in acute muscle architectural changes.

Key points

• Three squat protocols using moderate intensity (75% 1-RM; 3 sets x 10 repetitions), high intensity (90% 1-RM, 3 sets x 3 repetitions) and maximal intensity (100% 1RM; 1 set x 1repetition) were unable to potentiate jump height or jump power in experienced, resistance trained men.
• Experienced, resistance trained athletes who are not competitive may be limited in regards to potentiation due to a poor level of conditioning.
• Both the moderate and high intensity potentiation protocols stimulated acute changes in muscle architecture. Greater increases in the CSA of both the RF and VL muscles were noted.
• A different potentiation protocol may have elicited greater changes in muscle architecture.

Key words: Resistance Exercise, Athletes, Sport, Squats, Performance     

Effect of Different Rest Intervals on the Exercise Volume Completed During Squat Bouts

The purpose of this research was to compare effect 3 different rest intervals on the squat volume completed during a workout. Twenty college-aged men volunteered to participate in this study (age 20.73 ± 2.60 years; body mass 80.73 ± 10.80 kg). All subjects performed 3 testing sessions, during which 4 sets of the squat was performed with 85% of a 1RM load. During each testing session, the squat was performed with a 1, 2, or 5-minute rest interval between sets. Volume was defined as the total number of repetitions completed over 4 sets for each rest condition. Statistical analysis was conducted separately for the squat. One-way repeated analyses of variance with Bonferroni post hocs demonstrated significant differences between each rest condition for both exercises tested (p < 0.05). The 5-minute rest condition resulted in the highest volume completed, followed in descending order by the 2- and 1-minute rest conditions. The ability to perform a higher volume of training with a given load may stimulate greater strength adaptations.

Key Points

• There is no significant difference in the squat volume between the 1- and 2-minute rest conditions.
• A 5-minute rest interval between sets allow for the highest volume to be completed when training with 85% of a 1RM load.

Key words: Strength training, recovery, squat, recruitment     

Effects of Instability Versus Traditional Resistance Training on Strength,Power and Velocity in Untrained Men

The purpose of this study was compare the effects of a traditional and an instability resistance circuit training program on upper and lower limb strength, power, movement velocity and jumping ability. Thirty-six healthy untrained men were assigned to two experimental groups and a control group. Subjects in the experimental groups performed a resistance circuit training program consisting of traditional exercises (TRT, n = 10) or exercises executed in conditions of instability (using BOSU® and TRX®) (IRT, n = 12). Both programs involved three days per week of training for a total of seven weeks. The following variables were determined before and after training: maximal strength (1RM), average (AV) and peak velocity (PV), average (AP) and peak power (PP), all during bench press (BP) and back squat (BS) exercises, along with squat jump (SJ) height and counter movement jump (CMJ) height. All variables were found to significantly improve (p <0.05) in response to both training programs. Major improvements were observed in SJ height (IRT = 22.1%, TRT = 20.1%), CMJ height (IRT = 17.7%, TRT = 15.2%), 1RM in BS (IRT = 13.03%, TRT = 12.6%), 1RM in BP (IRT = 4.7%, TRT = 4.4%), AP in BS (IRT = 10.5%, TRT = 9.3%), AP in BP (IRT = 2.4%, TRT = 8.1%), PP in BS (IRT=19.42%, TRT = 22.3%), PP in BP (IRT = 7.6%, TRT = 11.5%), AV in BS (IRT = 10.5%, TRT = 9.4%), and PV in BS (IRT = 8.6%, TRT = 4.5%). Despite such improvements no significant differences were detected in the posttraining variables recorded for the two experimental groups. These data indicate that a circuit training program using two instability training devices is as effective in untrained men as a program executed under stable conditions for improving strength (1RM), power, movement velocity and jumping ability.

Key Points

• Similar adaptations in terms of gains in strength, power, movement velocity and jumping ability were produced in response to both training programs.
• Both the stability and instability approaches seem suitable for healthy, physically-active individuals with or with limited experience in resistance training.
• RPE emerged as a useful tool to monitor exercise intensity during instability strength training.

Key words: Unstable surfaces, strength training, back squat, bench press, jumping ability     

Higher Cardiorespiratory Fitness in Older Trained Women is Due to Preserved Stroke Volume

Previous literature has shown that sedentary older women rely on peripheral adaptations to improve cardiorespiratory fitness with endurance training i.e. they show minimal increases in central parameters (cardiac output, Q) in response to endurance training. The purpose of this study therefore was to determine whether endurance trained older women were able to preserve maximal exercise Q and were characterized by a high stroke volume (SV) when compared to physically inactive older women. Trained (n = 7) and untrained (n = 1 0) women attended two maximal and one submaximal laboratory session. Breath-by-breath analysis was conducted using mass spectrometry and Q was assessed using acetylene open circuit inert gas wash-in. Multivariate analysis of variance and paired samples t-tests were used to determine between and within group differences. Trained women had a significantly higher VO_2max (37.5 vs. 24.1 ml^-1·kg·min^-1) compared to untrained women. There were no differences for peripheral oxygen extraction (VO₂/Q) at either submaximal or maximal work rates; however trained women had a significantly higher SV at maximal (119.3 vs. 94.6 ml) exercise compared to untrained women. In both trained and untrained women, SV did not rise significantly between submaximal and maximal exercise. Conclusion: Highly fit, endurance trained older women are able to preserve central parameters of VO_2max. Peripheral oxygen extraction is similar between older trained and untrained women.

Key points

• Older women are able to preserve stroke volume with high volumes of endurance training.
• Stroke volume of endurance trained older women does not continue to rise until maximal exercise, as is the case in young endurance trained adults.
• Peripheral oxygen extraction does not differ between endurance trained and physically inactive older women.

Key words: cardiac output, aging, exercise, running, VO_2max     

Comparison Between Pre-Exhaustion and Traditional Exercise Order on Muscle Activation and Performance in Trained Men

The purpose of this study was to measure the acute effects of pre-exhaustion vs. traditional exercise order on neuromuscular performance and sEMG in trained men. Fourteen young, healthy, resistance trained men (age: 25.5 ± 4.0 years, height: 174.9 ± 4.1 cm, and total body mass: 80.0 ± 11.1 kg) took part of this study. All tests were randomized and counterbalanced for all subjects and experimental conditions. Volunteers attended one session in the laboratory. First, they performed ten repetition maximum (10RM) tests for each exercise (bench press and triceps pushdown) separately. Secondly, they performed all three conditions at 10RM: pre-test (bench press and triceps pushdown, separately), pre-exhaustion (triceps pushdown+bench press, PE) and traditional (bench press+triceps pushdown, TR), and rested 30 minutes between conditions. Results showed that pre-test was significantly greater than PE (p = 0.031) but not different than TR, for total volume load lifted. There was a significant difference between the pre-test and the time-course of lactate measures (p = 0.07). For bench press muscle activity of the pectoralis major, the last repetition was significantly greater than the first repetition (pre-test: p = 0.006, PE: p = 0.016, and TR: p = 0.005). Also, for muscle activity of the triceps brachii, the last repetition was significantly greater than the first repetition (pre-test: p = 0.001, PE: p = 0.005, and TR: p = 0.006). For triceps pushdown, muscle activity of the triceps brachii, the last repetition was significantly greater than the first repetition (pre-test: p = 0.006, PE: p = 0.016, and TR: p = 0.005). For RPE, there were no significant differences between PE and TR (p = 0.15). Our results suggest that exercise order decreases repetitions performed, however, neuromuscular fatigue, lactate, and RPE are not impacted. The lack of difference in total volume load lifted between PE and TR might explain, at least in part, the similar metabolic and perceptual responses.

Key points

• The effects of different exercise order schemes (e.g. PE and TR) on muscle activity and strength performance indicated that similar responses were observed when comparing these schemes.
• Strength and conditioning coaches should consider these results when prescribing resistance training programs.
• The primary target (e.g. muscle group) of the training session should trained first, when fatigue level low, in order to maximize training outcomes.

Key words: Exercise performance, resistance training, biomechanics     

The Acute Effects of Back Squats on Vertical Jump Performance in Men and Women

The aim of the present study was to investigate the acute effects of performing back squats on subsequent performance during a series of vertical jumps in men and women. Twelve men and 12 women were tested on three separate occasions, the first of which was used to determine their 1-repetition maximum (1-RM) parallel back squat. Following this, subjects performed a potentiation and a control treatment in a counterbalanced order. The potentiation treatment culminated with subjects performing parallel back squats with a load equivalent to 70% 1- RM for three repetitions, following which they performed one countermovement vertical jump (CMJ) for maximal height every three minutes for a total of 10 jumps. During the control treatment, subjects performed only the CMJs. Jump height (JH) and vertical stiffness (VStiff) were calculated for each jump from the vertical force signal recorded from a force platform. There were no significant changes in JH or VStiff following the treatments and no significant differences in the responses between men and women (p > 0.05). Correlations between normalized 1-RM back squat load and the absolute change in JH and VStiff were small to moderate for both men and women, with most correlations being negative. Large variations in response to the back squats were noted in both men and women. The use of resistance exercises performed prior to a series of vertical jumps can result in improvements in performance in certain individuals, although the gains tend to be small and dependent upon the mechanical variable measured. There does not seem to be any differences between men and women in the response to dynamic potentiation protocols.

Key points

• Substantial individual responses were noted in both men and women in response to the PAP protocol used in the present study.
• The choice of dependent variable influences the ef-ficacy of the PAP protocol, with JH and VStiff demonstrating disparate responses in individual sub-jects.Such individual responses may render such PAP protocols impractical for strength and conditioning practitioners as the protocols are likely to require in-dividualizing to each athlete.

Key words: Back squats, vertical jump, potentiation, vertical stiffness     

Reliability of the One-Repetition Maximum Test Based on Muscle Group and Gender

The purpose of the present study was to examine the influence of muscle group location and gender on the reliability of assessing the one-repetition maximum (1RM) test. Thirty healthy males (n = 15) and females (n = 15) who experienced at least 3 months of continuous resistance training during the last 2 years aged 18-35 years volunteered to participate in the study. The 1RM for the biceps curl, lat pull down, bench press, leg curl, hip flexion, triceps extension, shoulder press, low row, leg extension, hip extension, leg press and squat were measured twice by a trained professional using a standard published protocol. Biceps curl, lat pull down, bench press, leg curl, hip flexion, and squat 1RM''s were measured on the first visit, then 48 hours later, subjects returned for their second visit. During their second visit, 1RM of triceps extension, shoulder press, low row, leg extension, hip extension, and leg press were measured. One week from the second visit, participants completed the 1 RM testing as previously done during the first and second visits. The third and fourth visits were separated by 48 hours as well. All four visits to the laboratory were at the same time of day. A high intraclass correlation coefficient (ICC > 0.91) was found for all exercises, independent of gender and muscle group size or location, however there was a significant interaction for muscle group location (upper body vs. lower body) in females (p < 0.027). In conclusion, a standardized 1RM testing protocol with a short warm-up and familiarization period is a reliable measurement to assess muscle strength changes regardless of muscle group location or gender.

Key points

• The one repetition maximum (1RM) test is considered the gold standard for assessing muscle strength in non-laboratory situations.
• This study was done to examine the influence of muscle group location and gender on the reliability of assessing the 1RM test.
• The standardized 1RM testing protocol with a short warm-up and familiarization period is a reliable measurement technique to assess muscle strength changes regardless of muscle group location or gender.

Key words: Reliability, 1RM, resistance exercise     

Effect of Energy Expenditure and Training Status on Leptin Response to Sub-Maximal Cycling

We examined the leptin response and related hormones during and after two sub-maximal exercise protocols in trained and untrained subjects. During this study, plasma concentrations of leptin [Lep], insulin [I], cortisol [C], growth hormone [GH], glucose [G] and lactate [La] were measured. 7 elite volleyball trained players (TR) and 7 untrained (UTR) subjects (percent body fat: 13.2 ± 1.8 versus 15.7 ± 1.0, p < 0.01, respectively) were examined after short and prolonged sub-maximal cycling exercise protocols (SP and PP). Venous blood samples were collected before each protocol, during, at the end, and after 2 and 24 h of recovery. SP and PP energy expenditures ranged from 470 ± 60 to 740 ± 90 kcal for TR and from 450 ± 60 to 710 ± 90 kcal for UTR, respectively. [Lep] was related to body fat percentage and body fat mass in TR (r = 0. 84, p < 0.05 and r = 0.93, p < 0.01) and in UTR (r = 0.89, p < 0.01 and r = 0.92, p < 0. 01, respectively). [Lep] did not change significantly during both protocols for both groups but was lower (p < 0.05) in all sampling in TR when compared to UTR. Plasma [I] decreased (p < 0.01) and [GH] increased (p < 0.01) significantly during both SP and PP and these hormones remained lower (I: p < 0.01) and higher (GH: p < 0.01) than pre-exercise levels after a 2-h recovery period, returning to base-line at 24-h recovery. Plasma [La] increased (p < 0.01) during both protocols for TR and UTR. There was no significant change in [C] and [G] during and after both protocols for all subjects. It is concluded that 1) leptin is not sensitive to acute short or prolonged sub-maximal exercises (with energy expenditure under 800 kcal) in volleyball/ anaerobically trained athletes as in untrained subjects, 2) volleyball athletes showed significantly lower resting and exercise leptin response with respect to untrained subjects and 3) it appears that in these anaerobically trained athletes leptin response to exercise is more sensitive to the level of energy expenditure than hormonal or metabolic modifications induced by acute exercise.

Key points

• Trials concerning acute exercise and leptin indicated discrepant results.
• Acute exercise with energy expenditure higher than 800 kcal can decrease leptinemia.
• Elite volleyball players presented decreased leptin levels than untrained subjects.

Key words: Hormones, anaerobic training, acute exercise, body fat.     

Reliability and Validity of the Polar V800 Sports Watch for Estimating Vertical Jump Height

This study aimed to assess the reliability and validity of the Polar V800 to measure vertical jump height. Twenty-two physically active healthy men (age: 22.89 ± 4.23 years; body mass: 70.74 ± 8.04 kg; height: 1.74 ± 0.76 m) were recruited for the study. The reliability was evaluated by comparing measurements acquired by the Polar V800 in two identical testing sessions one week apart. Validity was assessed by comparing measurements simultaneously obtained using a force platform (gold standard), high-speed camera and the Polar V800 during squat jump (SJ) and countermovement jump (CMJ) tests. In the test-retest reliability, high intraclass correlation coefficients (ICCs) were observed (mean: 0.90, SJ and CMJ) in the Polar V800. There was no significant systematic bias ± random errors (p > 0.05) between test-retest. Low coefficients of variation (<5%) were detected in both jumps in the Polar V800. In the validity assessment, similar jump height was detected among devices (p > 0.05). There was almost perfect agreement between the Polar V800 compared to a force platform for the SJ and CMJ tests (Mean ICCs = 0.95; no systematic bias ± random errors in SJ mean: -0.38 ± 2.10 cm, p > 0.05). Mean ICC between the Polar V800 versus high-speed camera was 0.91 for the SJ and CMJ tests, however, a significant systematic bias ± random error (0.97 ± 2.60 cm; p = 0.01) was detected in CMJ test. The Polar V800 offers valid, compared to force platform, and reliable information about vertical jump height performance in physically active healthy young men.Key points

• The Polar V800 sports watch was shown to be a reliable and valid tool for measuring jumping ability.
• The Polar V800 is a simple, multifunctional, inexpensive and practical device that offers adequate information about the vertical jump height performance in physically active healthy young men.
• It would also be interesting to demonstrate the reliability and validity of the Polar V800 sports watch to assess vertical jump height in highly trained athletes or other populations.

Key words: Jumping ability, squat jump, countermovement jump, pulsometer, Bland Altman plot, intraclass correlation coefficient     

Ventilation Behavior in Trained and Untrained Men During Incremental Test: Evidence of one Metabolic Transition Point

This study aimed to describe and compare the ventilation behavior during an incremental test utilizing three mathematical models and to compare the feature of ventilation curve fitted by the best mathematical model between aerobically trained (TR) and untrained (UT) men. Thirty five subjects underwent a treadmill test with 1 km·h^-1 increases every minute until exhaustion. Ventilation averages of 20 seconds were plotted against time and fitted by: bi-segmental regression model (_2SRM); three-segmental regression model (3SRM); and growth exponential model (GEM). Residual sum of squares (RSS) and mean square error (MSE) were calculated for each model. The correlations between peak VO₂ (VO_2PEAK), peak speed (Speed_PEAK), ventilatory threshold identified by the best model (VT_2SRM) and the first derivative calculated for workloads below (moderate intensity) and above (heavy intensity) VT_2SRM were calculated. The RSS and MSE for GEM were significantly higher (p < 0.01) than for _2SRM and 3SRM in pooled data and in UT, but no significant difference was observed among the mathematical models in TR. In the pooled data, the first derivative of moderate intensities showed significant negative correlations with VT_2SRM (r = -0.58; p < 0.01) and Speed_PEAK (r = -0.46; p < 0.05) while the first derivative of heavy intensities showed significant negative correlation with VT_2SRM (r = -0. 43; p < 0.05). In UT group the first derivative of moderate intensities showed significant negative correlations with VT_2SRM (r = -0.65; p < 0.05) and Speed_PEAK (r = -0.61; p < 0.05), while the first derivative of heavy intensities showed significant negative correlation with VT_2SRM (r= -0.73; p< 0.01), Speed_PEAK (r = -0.73; p < 0.01) and VO_2PEAK (r = -0.61; p < 0.05) in TR group. The ventilation behavior during incremental treadmill test tends to show only one threshold. UT subjects showed a slower ventilation increase during moderate intensities while TR subjects showed a slower ventilation increase during heavy intensities.

Key points

• The increase of ventilation during incremental exercise tends to show only one metabolic transition point.
• The presence of a threshold process or a continuous process in ventilation during incremental exercise seems to be only a methodological matter.
• The ventilatory efficiency can be employed to distinguish trained than untrained subjects once this index is associated with aerobic parameters. When analyzed the whole curve, trained subjects show a better ventilatory efficiency at heavy intensities and untrained subjects show a better ventilatory efficiency at moderate intensities.

Key words: Ventilatory threshold, mathematical modeling, ventilatory responses, aerobic training status     

Salivary Cortisol Responses and Perceived Exertion during High Intensity and Low Intensity Bouts of Resistance Exercise

The purpose of this study was to measure the salivary cortisol response to different intensities of resistance exercise. In addition, we wanted to determine the reliability of the session rating of perceived exertion (RPE) scale to monitor resistance exercise intensity. Subjects (8 men, 9 women) completed 2 trials of acute resistance training bouts in a counterbalanced design. The high intensity resistance exercise protocol consisted of six, ten-repetition sets using 75% of one repetition maximum (RM) on a Smith machine squat and bench press exercise (12 sets total). The low intensity resistance exercise protocol consisted of three, ten-repetition sets at 30% of 1RM of the same exercises as the high intensity protocol. Both exercise bouts were performed with 2 minutes of rest between each exercise and sessions were repeated to test reliability of the measures. The order of the exercise bouts was randomized with least 72 hours between each session. Saliva samples were obtained immediately before, immediately after and 30 mins following each resistance exercise bout. RPE measures were obtained using Borg’s CR-10 scale following each set. Also, the session RPE for the entire exercise session was obtained 30 minutes following completion of the session. There was a significant 97% increase in the level of salivary cortisol immediately following the high intensity exercise session (P<0.05). There was also a significant difference in salivary cortisol of 145% between the low intensity and high intensity exercise session immediately post-exercise (P<0.05). The low intensity exercise did not result in any significant changes in cortisol levels. There was also a significant difference between the session RPE values for the different intensity levels (high intensity 7.1 vs. low intensity 1.9) (P<0.05). The intraclass correlation coefficient for the session RPE measure was 0.95. It was concluded that the session RPE method is a valid and reliable method of quantifying resistance exercise and that salivary cortisol responds promptly to the exercise load.

Key Points

• The present study showed that salivary cortisol responses were significantly different immediately post exercise between the low intensity and high intensity exercise sessions
• Salivary measures of cortisol can be used to delineate between high and low intensity resistance exercise bouts.
• The session RPE method appears to be a reliable method of quantifying resistance exercise

Key words: Weight lifting, stress, endocrine effects     

Seasonal Strength Performance and Its Relationship with Training Load on Elite Runners

The aim of this study was to analyze the time-course of force production of elite middle and long-distance runners throughout an entire season and at the end of the off-season, as well as its relationships with training load and hormonal responses. Training load was recorded daily throughout an entire season by measuring and evaluating the session distance (km), training zone and session-RPE in a group of 15 elite middle and long-distance runners (12 men, 3 women; age = 26.3 ± 5.1yrs, BMI = 19.7 ± 1.1). Also, basal salivary-free cortisol levels were measured weekly, and 50-metre sprints, mean propulsive velocity (MPV), mean propulsive power (MPP), repetition maximum (RM) and peak rate of force development (RFD) of half-squats were measured 4 times during the season, and once more after the off-season break. There were no significant variations in force production during the season or after the off-season break, except for the RFD (-30.2%, p = 0.005) values, which changed significantly from the beginning to the end of the season. Significant correlations were found between session-RPE and MPV (r = -0.650, p = 0.004), MPP (r = -0.602, p = 0.009), RM (r = -0.650, p = 0.004), and the 50-metre sprint (r = 0.560, p = 0.015). Meanwhile, salivary-free cortisol correlated significantly with the 50-metre sprint (r = 0.737, p < 0.001) and the RM ( r = -0.514, p = 0.025). Finally, the training zone correlated with the 50-metre sprint (r = -0.463, p = 0.041). Session-RPE, training zone and salivary-free cortisol levels are related to force production in elite middle and long-distance runners. Monitoring these variables could be a useful tool in controlling the training programs of elite athletes.

Key points

• Session-RPE, training zone and salivary free cortisol levels correlate significantly with strength-related variables in middle and long-distance elite runners.
• A month of active rest during the off-season break is enough to prevent decreases in force production of such athletes.
• Monitoring training loads through session-RPE is a suitable and simple method for controlling the training process in elite middle and long-distance runners.

Key words: Endurance, exercise, testing, physiology     

Effect of Exercise Intensity on Differentiated and Undifferentiated Ratings of Perceived Exertion During Cycle and Treadmill Exercise in Recreationally Active and Trained Women

The purpose of the study is to examine the effect of aerobic exercise intensity on components of the differentiated perceived exertion model in young women performing weight bearing and non-weight bearing aerobic exercise. Subjects were 18-25 yr old women who were recreationally active (n = 19; VO₂max = 33.40 ml·kg^-1·min^-1) and trained (N = 22; VO₂max = 43.3 ml·kg^-1·min^-1). Subjects underwent two graded exercise tests (GXT) on a treadmill and bike which were separated by 48 hours. RPE-Overall, -Legs, and -Chest, as well as oxygen uptake (VO₂) and heart rate were recorded each minute. Individual regression analyses were used to identify RPE-Overall,-Legs, and -Chest at 40, 60, 80% VO_2max/peak. Separate two factor (site (3) x intensity (3)) ANOVAs with repeated measures on site and intensity were computed for each training status. Furthermore, RPE responses were also examined with a one factor (site (3)) within subject ANOVA with repeated measure on site at the ventilatory breakpoint. For both the recreationally active and trained groups no significant differences were observed for RPE-Overall, -Legs, and -Chest during treadmill exercise. However, for cycling exercise results indicated that RPE-Legs was significantly greater at all exercise intensities than RPE-Overall and RPE-Chest for trained subjects while for recreationally active subjects RPE-Legs was only significantly higher at the highest exercise intensity. Responses at the ventilatory breakpoint during cycle exercise indicated that RPE-Legs was significantly greater than RPE-Chest and RPE-Overall for trained subjects but not for recreationally active subjects. Signal dominance was not observed at an intensity equivalent to the ventilatory breakpoint during treadmill exercise in either of the groups. In recreationally active and trained females signal dominance was demonstrated only during cycling exercise, but not during treadmill exercise. Signal integration could not be demonstrated during cycling and treadmill exercise at various intensities.

Key points

• RPE is a valid tool to track relative exercise intensity and can be applied as differentiated and undifferentiated responses regardless of training status.
• RPE-Legs dominated the signal response in trained women during cycling exercise.
• RPE-Legs, -Chest, and -Overall did not differ significantly in trained and recreationally active women during treadmill exercise.
• RPE-Legs and -Chest contribute equally to the formation of RPE-Overall during cycling and treadmill exercise.

Key words: Aerobic exercise, physical exertion, oxygen consumption, physical fitness     

Effect of Load on Peak Power of the Bar,Body and System during the Deadlift

The purpose of this investigation was to examine how load would affect peak power (PP) of the bar, body and system (bar + body) during the deadlift. Eight healthy males (age = 22.00 ± 2.38 years; height = 1.80 ± 0.05 m; body mass = 88.97 ± 14.88 kg; deadlift one repetition maximum [1RM] = 203.44 ± 21.59 kg, 1RM/BM = 2.32 ± 0.31) with a minimum of 2 years’ resistance training experience and a deadlift 1RM over 1.5 times their bodyweight participated in the investigation. During the first session, anthropometric data were recorded and a 1RM deadlift was obtained from the participants. During the second session, participants performed two repetitions at intensities of 30, 40, 50, 60, 70, 80 and 90% of their 1RM in a randomized order. Three-dimensional videography with a force plate was used for data collection and analysis. Peak force (PF), peak velocity (PV), an d PP were calculated for the bar, body, and system (bar + body) during the deadlift. PP occurred at 50%, 30%, and 70% of 1RM for the bar, body, and system, respectively. The optimal loading for the deadlift exercise may vary depending on the desired stimulus and whether the bar, body, or system variables are of most interest.

Key points

• Peak power of the bar, body and system vary depending upon load.
• Loading should be chosen according to desired training effect, with considerations for sport specificity.
• Additional exercises should be investigated concerning the effect of various loads on power.

Key words: Deadlift, peak power, force plate, resistance training