Exercise Performance and Muscle Contractile Properties After Creatine Monohydrate Supplementation in Aerobic-Anaerobic Training Rats

The purpose of this study was to investigate the effects of creatine monohydrate supplementation on exercise performance and contractile variables in aerobic-anaerobic training rats. Twenty 90-day-old male Sprague Dawley rats were divided into two groups - creatine (Cr) and controls (K). The creatine group received creatine monohydrate as a nutritional supplement, whereas the control group was given placebo. Both groups were trained 5 days a week on a treadmill for 20 days in a mixed (aerobic-anaerobic) metabolic working regimen (27 m·min^-1, 15% elevation for 40 min). The exercise performance (sprint-test), contractile properties (m. tibialis anterior), oxidative enzyme activity (SDH, LDH, NADH₂) in m. soleus and blood hematological and chemical variables were assessed in the groups at the end of the experiment. It was found out that creatine supplementation improved the exercise performance after 20 days of administration in a dose of 60 mg per day on the background of a mixed (aerobic-anaerobic) exercise training. At the end of the trial the Cr-group demonstrated better values for the variables which characterize the contractile properties of m. tibialis anterior containing predominantly types IIA and IIB muscle fibers. On the other hand, a higher oxidative capacity was found out in m. soleus (type I muscle fibers) as a result of 20-day creatine supplementation. No side effects of creatine monohydrate supplementation were assessed by the hematological and blood biochemical indices measured in this study.

Key points

• The creatine monohydrate supplementation of the rats diet improves their exercise performance after 20 days administration in a dose of 60 mg per day on the background of a mixed (aerobic-anaerobic) exercise training.
• The creatine supplemented rats demonstrate better contractile properties of m. tibialis anterior which muscle contains predominantly types IIA and IIB muscle fibers.
• The soleus muscle (type I muscle fibers) demonstrates a higher oxidative capacity as a result of 20-days creatine supplementation.

Key words: Exercise, creatine supplementation, rats, performance, muscle contractile properties     

Effect of Different Rest Intervals,Between Sets,on Muscle Performance During Leg Press Exercise,in Trained Older Women

The purpose of this study was to assess the effect of different rest intervals (RI) between sets on number of repetitions, sustainability of repetitions, and total volume during a leg press exercise. Seventeen resistance-trained older women (68.0 ± 5.9 years, 71. 2 ± 11.7 kg, 1.58 ± 0.07 m) participated in the study. All participants performed three sets to voluntary exhaustion, with loads that corresponded to 15 maximum repetitions, in two experimental sessions (that ranged from 48 to 72 hours apart). In each session, one of two RI (one-minute: RI-1 and three minute: RI-3) was tested, employing a randomized and counterbalanced design. For both RI, significant reductions (p < 0.05) were observed in the number of repetitions and sustainability of repetitions, from the first to the second and third sets. Differences (p < 0.05) between the RI also were observed in the two final sets. The total volume for the RI-3 session was statistically higher (29.4%, p < 0.05) as compared to the RI-1 session. The length of the RI between sets influenced the number of repetitions, sustainability of repetitions, and total volume. The longer RI should be used, therefore, when the goal of training is to increase the total volume.

Key points

• This study examined the influence of rest intervals, between sets, on muscle performance during leg press exercise, in trained older women.
• When multiple sets were performed to voluntary exhaustion, neither short and long rest interval (1 and 3 minutes, respectively) promoted the sustainability of repetitions in subsequent sets.
• A longer rest interval seems to be necessary for a higher number of repetitions in subsequent sets, and with increase in time of tension and total volume.

Key words: Aging, muscle fatigue, muscle endurance, recovery.     

The Occurrence of Core Muscle Fatigue During High-Intensity Running Exercise and its Limitation to Performance: The Role of Respiratory Work

This study investigated the occurrence of core muscle fatigue during high-intensity running exercise and its limitation to exercise performance. A secondary aim was to investigate whether respiratory muscle work performed during intense running periods, would contribute to core muscle fatigue. Nine male recreational runners were recruited for two reasons; (1) to perform a continuous treadmill run at 85% VO₂max with and without core muscle fatigue in the CR_F and CR trials, respectively; and (2) to mimic the treadmill run-induced respiratory response recorded in the CR trial while subjects were free of whole-body exercise (Mimic trial). The changes in global core muscle function with fatigue in this study were evaluated by performing a sport-specific endurance plank test (SEPT), and the associated influence on running performance was examined by comparing the time to exhaustion during the treadmill run between the CR and CR_F trials. Subsequent to the treadmill run in the CR trial, SEPT (255.7 ± 85.3 vs 177.3 ± 80.6 s) was reduced from baseline in all runners. The reduction correlated (r = 0.67) with the concomitant decline in inspiratory muscle function revealed by maximal inspiratory mouth pressure (PI_max: 151.3 ± 18.2 vs 133.3 ± 17.2 cmH₂O, p < 0.05). In the Mimic trial, similar results in SEPT (212.3 ± 90.2 s), PI_max (129.0 ± 26.7 cmH₂O), and correlation (r = 0.77, p < 0.05) were observed following voluntary hyperpneic activity. With the preceded fatigued core muscle workout in the CR_F trial, the running capacity was impaired significantly (10.7 ± 4.5 vs 6.5 ± 2.0 min, p < 0.05). The impairment was correlated (r=0.72) to the SEPT reduction resulting from the workout. The results suggest that a high-intensity maximum run may induce core muscle fatigue in runners. The core muscle fatigue, which may be partly attributed to the corresponding respiratory work, may limit their running endurance. Inspiratory muscle function appears to be essential for core stabilization during the intense running.

Key points

• A high-intensity maximum run may induce core muscle fatigue in runners. The core muscle fatigue, which may be partly attributed to the corresponding respiratory work, may limit their running endurance.
• In support of previous notion, inspiratory muscles may share the work of core stabilization during intense exercise, while simultaneously increasing the demand for breathing.
• Inspiratory muscle training incorporated into a running specific-core training regime potentially enhances the training effect on the core muscles in a functional manner to deal with the challenges faced during intense exercise.

Key words: Core stability, muscle function, respiratory muscle, plank test     

不同肌松程度对脊柱手术皮层体感诱发电位的监测

目的：了解新型肌肉松弛药顺式阿曲库铵用于脊柱外科手术,肌松程度对皮层体感诱发电位（CSEP）监测的影响。方法：选择ASAI～II级,择期脊柱外科手术病人60例,随机分为6组。在首次推注插管剂量的顺式阿曲库铵后,连续监测T1,以肌松监测反馈调控输注模式调整不同剂量进行输注,维持各分组所要求的不同肌松程度,观察6组病例术中CSEP的P40波的波幅及潜伏期。同时对肌松分级进行主观评定。结果：在不同的肌松程度下,IV组、V组及VI组患者的波幅与基准值比较有统计学差异（P〈0.05）;I组、II组、III组患者的波幅与基准值比较无统计学差异（P〉0.05）。肌松主观评定,V组、VI组患者肌松评价差的例数与I组、II组、III组、IV组比较有统计学差义（P〈0.05）。结论：能满足CSEP监测的要求,同时也能满足手术及运动诱发电位监测需要的肌松程度是T1值在0～15%。     

The Mark Coventry Award: In Vivo Knee Forces During Recreation and Exercise After Knee Arthroplasty

Knee forces directly affect arthroplasty component survivorship, wear of articular bearing surfaces, and integrity of the bone-implant interface. It is not known which activities generate forces within a range that is physiologically desirable but not high enough to jeopardize the survivorship of the prosthetic components. We implanted three patients with an instrumented tibial prosthesis and measured knee forces and moments in vivo during exercise and recreational activities. As expected, stationary bicycling generated low tibial forces, whereas jogging and tennis generated high peak forces. On the other hand, the golf swing generated unexpectedly high forces, especially in the leading knee. Exercise on the elliptical trainer generated lower forces than jogging but not lower than treadmill walking. These novel data allow for a more scientific approach to recommending activities after TKA. In addition, these data can be used to develop clinically relevant structural and tribologic testing, which may result in activity-specific knee designs such as a knee design more tolerant of golfing by optimizing the conflicting needs of increased rotational laxity and conformity.     

Effect of Heat Preconditioning by Microwave Hyperthermia on Human Skeletal Muscle After Eccentric Exercise

The purpose of this study was to clarify whether heat preconditioning results in less eccentric exercise-induced muscle damage and muscle soreness, and whether the repeated bout effect is enhanced by heat preconditioning prior to eccentric exercise. Nine untrained male volunteers aged 23 ± 3 years participated in this study. Heat preconditioning included treatment with a microwave hyperthermia unit (150 W, 20 min) that was randomly applied to one of the subject’s arms (MW); the other arm was used as a control (CON). One day after heat preconditioning, the subjects performed 24 maximal isokinetic eccentric contractions of the elbow flexors at 30°·s^-1 (ECC1). One week after ECC1, the subjects repeated the procedure (ECC2). After each bout of exercise, maximal voluntary contraction (MVC), range of motion (ROM) of the elbow joint, upper arm circumference, blood creatine kinase (CK) activity and muscle soreness were measured. The subjects experienced both conditions at an interval of 3 weeks. MVC and ROM in the MW were significantly higher than those in the CON (p < 0.05) for ECC1; however, the heat preconditioning had no significant effect on upper arm circumference, blood CK activity, or muscle soreness following ECC1 and ECC2. Heat preconditioning may protect human skeletal muscle from eccentric exercise-induced muscle damage after a single bout of eccentric exercise but does not appear to promote the repeated bout effect after a second bout of eccentric exercise.

Key points

• There have been few studies about the effects of heat preconditioning on muscle damage caused by eccentric exercise and the repeated bout effect after a second bout of eccentric exercise.
• Heat preconditioning with microwave hyperthermia may attenuate eccentric exercise-induced muscle damage.
• Heat preconditioning does not enhance the repeated bout effect.

Key words: delayed-onset muscle soreness, muscle damage, repeated bout effect, heat shock proteins     

Skeletal Muscle Force and Functional Exercise Tolerance Before and After Lung Transplantation: A Cohort Study

We investigated the impact of lung transplantation and outpatient pulmonary rehabilitation after lung transplantation on skeletal muscle function and exercise tolerance. Skeletal muscle force (Quadriceps force, QF), exercise tolerance (six minute walking distance, 6MWD) and lung function were assessed in 36 patients before and after lung transplantation. Seventeen male and 19 female patients (age 57 ± 4) showed skeletal muscle weakness before the transplantation. A further 32 ± 21% reduction was seen 1.2 (interquartile range 0.9 to 2.0) months after LTX. The number of days on the intensive care unit was significantly related to the observed deterioration in muscle force after LTX. At this time point 6MWD was comparable to pre-LTX.
Rehabilitation started 37 (IQR 29 to 61) days after LTX. 6MWD and QF improved significantly (140 ± 91 m, and 35 ± 48%, respectively; p < 0.05) with rehabilitation. QF remained below pre-LTX values. The evolution of the 6MWD with the transplantation and the subsequent rehabilitation was less in female compared to male subjects.
We conclude that muscle strength deteriorates after lung transplantation, particularly in patients with long ICU stay. Outpatient pulmonary rehabilitation is feasible after lung transplantation and leads to recovery of skeletal muscle function. In female patients this recovery is significantly less compared to male recipients.     

The Difference in Respiratory and Blood Gas Values During Recovery After Exercise With Spontaneous Versus Reduced Breathing Frequency

Extrapolation from post-exercise measurements has been used to estimate respiratory and blood gas parameters during exercise. This may not be accurate in exercise with reduced breathing frequency (RBF), since spontaneous breathing usually follows exercise. This study was performed to ascertain whether measurement of oxygen saturation and blood gases immediately after exercise accurately reflected their values during exercise with RBF. Eight healthy male subjects performed an incremental cycling test with RBF at 10 breaths per minute. A constant load test with RBF (B10) was then performed to exhaustion at the peak power output obtained during the incremental test. Finally, the subjects repeated the constant load test with spontaneous breathing (SB) using the same protocol as B10. Pulmonary ventilation (V_E), end-tidal oxygen (P_ETO₂), and carbon dioxide pressures (P_ETCO₂) and oxygen saturation (SaO₂) were measured during both constant load tests. The partial pressures of oxygen (PO₂) and carbon dioxide (PCO₂) in capillary blood were measured during the last minute of exercise, immediately following exercise and during the third minute of recovery. At the end of exercise RBF resulted in lower P_ETO₂, SaO₂ and PO₂, and higher P_ETCO₂ and PCO₂ when compared to spontaneous breathing during exercise. Lower SaO₂ and P_ETO₂ were detected only for the first 16s and 20s of recovery after B10 compared to the corresponding period in SB. There were no significant differences in PO₂ between SB and B10 measured immediately after the exercise. During recovery from exercise, P_ETCO₂ remained elevated for the first 120s in the B10 trial. There were also significant differences between SB and B10 in PCO₂ immediately after exercise. We conclude that RBF during high intensity exercise results in hypoxia; however, due to post-exercise hyperpnoea, measurements of blood gas parameters taken 15s after cessation of exercise did not reflect the changes in PO₂ and SaO₂ seen during exercise.

Key points

• In some sports, the environment is inappropriate for direct measurement of respiratory and blood gas parameters during exercise. To overcome this problem, extrapolation from post-exercise measurements has often been used to estimate changes in respiratory and blood gas parameters during exercise.
• The possibility of hypoxia and hypercapnia during exercise with reduced breathing frequency has been tested by measuring capillary blood sampled after the exercise.
• Reduced breathing frequency during high intensity exercise results in hypoxia; however, due to marked post-exercise hyperventilation, measurements of blood gas parameters taken 15 s after the cessation of exercise did not yield any changes in these parameters.
• Despite hyperventilation during recovery, hypercapnia could be detected by measuring blood gas parameters within 15 s after the exercise with reduced breathing frequency.

Key words: Constant load test, reduced breathing frequency, recovery, respiratory parameters, oxygen saturation, blood gas     

Increased Skeletal Muscle Capillarization Independently Enhances Insulin Sensitivity in Older Adults After Exercise Training and Detraining

Intramuscular signaling and glucose transport mechanisms contribute to improvements in insulin sensitivity after aerobic exercise training. This study tested the hypothesis that increases in skeletal muscle capillary density (CD) also contribute to exercise-induced improvements in whole-body insulin sensitivity (insulin-stimulated glucose uptake per unit plasma insulin [M/I]) independent of other mechanisms. The study design included a 6-month aerobic exercise training period followed by a 2-week detraining period to eliminate short-term effects of exercise on intramuscular signaling and glucose transport. Before and after exercise training and detraining, 12 previously sedentary older (65 ± 3 years) men and women underwent research tests, including hyperinsulinemic-euglycemic clamps and vastus lateralis biopsies. Exercise training increased Vo_2max (2.2 ± 0.2 vs. 2.5 ± 0.2 L/min), CD (313 ± 13 vs. 349 ± 18 capillaries/mm²), and M/I (0.041 ± 0.005 vs. 0.051 ± 0.007 μmol/kg fat-free mass/min) (P < 0.05 for all). Exercise training also increased the insulin activation of glycogen synthase by 60%, GLUT4 expression by 16%, and 5′ AMPK-α1 expression by 21%, but these reverted to baseline levels after detraining. Conversely, CD and M/I remained 15% and 18% higher after detraining, respectively (P < 0.05), and the changes in M/I (detraining minus baseline) correlated directly with changes in CD in regression analysis (partial r = 0.70; P = 0.02). These results suggest that an increase in CD is one mechanism contributing to sustained improvements in glucose metabolism after aerobic exercise training.     

Effect of Moderate Altitude on Peripheral Muscle Oxygenation During Leg Resistance Exercise in Young Males

Training at moderate altitude (~1800m) is often used by athletes to stimulate muscle hypoxia. However, limited date is available on peripheral muscle oxidative metabolism at this altitude (1800AL). The purpose of this study was to determine whether acute exposure to 1800AL alters muscle oxygenation in the vastus lateralis muscle during resistance exercise. Twenty young active male subjects (aged 16 – 21 yr) performed up to 50 repetitions of the parallel squat at 1800AL and near sea level (SL). They performed the exercise protocol within 3 h after arrival at 1800 AL. During the exercise, the changes in oxygenated hemoglobin (OxyHb) in the vastus lateralis muscle, arterial oxygen saturation (SpO₂), and heart rate were measured using near infrared continuous wave spectroscopy (NIRcws) and pulse oximetry, respectively. Changes in OxyHb were expressed by D_eff defined as the relative index of the maximum change ratio (%) from the resting level. OxyHb in the vastus lateralis muscle decreased dramatically from the resting level immediately after the start of exercise at both altitudes. The D_eff during exercise was significantly (p < 0.001) lower at 1800AL (60.4 ± 6.2 %) than at near SL (74.4 ± 7.6 %). SpO₂ during exercise was significantly (p < 0.001) lower at 1800AL (92.0 ± 1.7 %) than at near SL (96.7 ± 1.2 %). Differences (SL – 1800AL) in D_eff during exercise correlated fairly strongly with differences in SpO₂ during exercise (r = 0.660). These results suggested that acute exposure to moderate altitude caused a more dramatical decrease in peripheral muscle oxygenation during leg resistance exercise. It is salient to note, therefore, that peripheral muscle oxygenation status at moderate altitude could be evaluated using NIRcws and that moderate altitudes might be effectively used to apply hypoxic stress on peripheral muscles.

Key Points

• The change in muscle oxygenation during the parallel squat at 1800 altitude and near sea level was investigated using near infrared continuous wave spectroscopy (NIRcws)
• The muscle oxygenation during exercise at 1800 altitude decreased more dramatically compared to sea level.
• NIRcws could help to provide a better understanding of exercising muscle metabolism at moderate altitude.

Key words: NIRcws, muscle oxygenation, moderate altitude, parallel squat, SpO₂     

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     

Comparison of Supervised Exercise and Home Exercise After Ankle Fracture

Ankle fractures are common fractures of the lower extremities that have an incidence rate of 101 fractures per 100.000 person-years. It is not clear which rehabilitation intervention should be performed after an ankle fracture. The aims of this study are to compare the effectiveness of a supervised exercise program with that of a home exercise program and to determine and compare the costs of these programs. A supervised exercise program and a home exercise program were performed for 8 weeks. The supervised exercise group consisted of 35 patients (mean age 39.23 years), and the home exercise group consisted of 73 patients (mean age 41.78 years). The average follow-up was 27.86 ± 9.88 months. Demographic information, injury details, type and classification of fracture, pain severity, and ankle range of motion were recorded. The clinical outcomes were determined by using the Pain Disability Index, the American Orthopaedic Foot and Ankle Society Ankle-Hindfoot Score, and the Short-Form 36 Health Survey. Surgical and rehabilitation satisfaction was evaluated with the use of a numeric scale. American Orthopaedic Foot and Ankle Society Ankle-Hindfoot Scores were statistically significantly higher in the home exercise group (p = .036), and rehabilitation satisfaction of the supervised exercise group was statistically significantly better (p = .047). The total rehabilitation crude cost of a patient in the supervised exercise group is 1113.63 Turkish lira (310.25 U.S. dollars) versus 182.31 Turkish lira (50.79 U.S. dollars) in the home exercise group. Considering that the crude cost of the home exercise program is very low and clinical outcomes are satisfactory, we recommend that patients with surgically treated isolated ankle fractures be followed up with a postoperative home exercise program.     

Blood Supply to the Latissimus Dorsi Muscle and Muscle Performance During Co- or Counterpulsatile Stimulation for Circulatory Assist

Abstract: For the application of the latissimus dorsi muscle (LDM) to circulatory assist, the muscle is stimulated with co- or counterpulsation during the cardiac cycle. The purpose of this study was to evaluate the blood supply to the LDM and its muscular performance during each respective stimulation. The origin of the LDM was connected to a tension gauge, a potentiometer, and 1 kg of weight in series. The LDM was stimulated at a ratio of 1:1 of heart to muscle contraction for 10 min. Copulsatile stimulation made thoracodorsal arterial flow (TDF) pre dominant during cardiac diastole. In counterpulsatile stimulation, TDF occurred predominantly during cardiac systole. Between the 2 patterns of stimulation, no significant differences were observed in the mean TDF rate during 1 cardiac cycle. The maximal force, maximal contrac tion length, and power of the LDM also did not differ significantly. These results suggest that despite the difference of the TDF profile, LDM performance may be com parable between co- and counterpulsatile stimulation for the application of the LDM to circulatory assist.     

Heart Rate Variability Before and After Cycle Exercise in Relation to Different Body Positions

The purpose of this study was to assess the effect of three different body positions on HRV measures following short-term submaximal exercise. Thirty young healthy males performed submaximal cycling for five minutes on three different occasions. Measures of HRV were obtained from 5-min R to R wave intervals before the exercise (baseline) and during the last five minutes of a 15 min recovery (post-exercise) in three different body positions (seated, supine, supine with elevated legs). Measures of the mean RR normal-to-normal intervals (RRNN), the standard deviation of normal-to-normal intervals (SDNN), the root mean square of successive differences (RMSSD) and the low-frequency (LF) and the high-frequency (HF) spectral power were analyzed. Post-exercise RRNN, RMSSD were significantly higher in the two supine positions (p < 0. 01) compared with seated body position. Post-exercise ln LF was significantly lower in the supine position with elevated legs than in the seated body position (p < 0.05). No significant difference was found among the three different body positions for post-exercise ln HF (p > 0.05). Post-exercise time domain measures of HRV (RRNN, SDNN, RMSSD) were significantly lower compared with baseline values (p < 0.01) regardless body position. Post-exercise ln LF and ln HF in all three positions remained significantly reduced during recovery compared to baseline values (p < 0.01). The present study suggests that 15 minutes following short-term submaximal exercise most of the time and frequency domain HRV measures have not returned to pre-exercise values. Modifications in autonomic cardiac regulation induced by body posture present at rest remained after exercise, but the post-exercise differences among the three positions did not resemble the ones established at rest.

Key points

• Whether different body positions may enhance post-exercise recovery of autonomic regulation remains unclear.
• The absence of restoration of HRV measures after 15 minutes of recovery favor the existence of modifying effects of exercise on mechanisms underlying heart regulation.
• On the basis of discrepancies in HRV measures in different body positions pre- and post-exercise we argue that the pace of recovery of cardiac autonomic regulation is dependent on body posture.

Key words: Heart rate variability, recovery, exercise     

Changes in Indirect Markers of Muscle Damage and Tendons After Daily Drop Jumping Exercise with Rapid Load Increase

The aim of this study was to assess changes in indirect markers of muscle damage and type I collagen degradation, as well as, patellar and Achilles tendon morphological differences during nine daily drop-jumps sessions with constant load alternated with rapid increases in load to test the hypothesis that frequent drop-jump training results in negative muscular and tendon adaptation. Young men (n = 9) performed daily drop jump workouts with progression every 3 days in terms of number of jumps, platform height and squat amplitude. Voluntary and electrically evoked knee extensor torque, muscle soreness, blood plasma creatine kinase (CK) activity and carboxyterminal cross-linked telopeptide (ICTP), patellar and Achilles tendon thickness and cross-sectional area (CSA) were assessed at different time points during the training period and again on days 1, 3, 10 and 17 after the training. The findings were as follows: (1) steady decline in maximal muscle strength with major recovery within 24 hours after the first six daily training sessions; (2) larger decline in electrically induced muscle torque and prolonged recovery during last three training sessions; (3) increase in patellar and Achilles tendons CSA without change in thickness towards the end of training period; (4) increase in jump height but not in muscle strength after whole training period. Our findings suggest that frequent drop-jump sessions with constant load alternated with rapid increases in load do not induce severe muscle damage or major changes in tendons, nonetheless, this type of loading is not advisable for muscle strength improvement.

Key points

• Frequent drop jump training induces activation mode dependent muscle torque depression late in the training period.
• No significant changes in the thickness of patellar and Achilles tendons are observed during frequent training, while CSA increases towards the end of training period.
• Longitudinal effect for jump height but not for muscle strength is evident after the whole training period.

Key words: Stretch-shortening cycle, neuromuscular adaptation, electrical stimulation, Achilles tendon, patellar tendon     

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