Isokinetics and Exercise Science

: Although whole body electromyostimulation (WB-EMS) has been shown to improve body composition and muscle strength in several research studies, it has not been confirmed whether a dose-response effect using various impulse-intensities exists and how they affect adipose tissue-derived adipokines (APK), body composition, and strength.

To investigate the dose-response effect of wearing a WB-EMS suit in conjunction with isometric exercise on adipokines (APK), body composition including thigh circumference, and thigh muscle strength in normal healthy men for 6 weeks.

Fifty-two male subjects were randomly assigned to one of four groups: control group (CON, n = 13), low impulse-intensity (LII) group ( n = 12), mid impulse-intensity (MII) group ( n = 14), and high impulse-intensity (HII) group ( n = 13). Low-, mid- and high-impulse intensities were set at 50%, 60% and 80% of maximum tolerance (1MT). Subjects in CON group wore WB-EMS suits, but did not receive any impulses. The WB-EMS suits used in this study enabled the simultaneous activation of eight muscle groups with selectable intensities. Stimulation frequency was selected at 85 Hz, impulse-width at 350 microsecond, and impulse-rise as a rectangular application. Impulse duration was 6 s with a 4 s break between impulses. The 20-minute WB-EMS sessions were combined with isometric exercises 3 times a week for 6 weeks. APK, body composition including thigh circumference, and isokinetic peak moment (PT) and work per repetition (WR) of the knee extensors and flexors were measured on Week 0, Week 2, Week 4, and Week 6.

Compared with the CON group, 1) there was a significant group by time interaction difference in Resistin ( P = 0.016). That is, Resistin increased in the CON and LII groups, but decreased in the MII and HII groups. These changes in Resistin for both groups began to appear at Week 4. 2) Body weight ( P = 0.024) and muscle mass ( P = 0.037) were significantly different in group by time interaction. The decrease of body weight in the HII group began to appear at Week 4. In particular, the level of muscle mass increased only in the HII group at Week 6. 3) There were significant group by time interaction differences in the circumferences of thigh subcutaneous fat (TSF) and thigh total fat (TTF) on right and left sides. The right TSF ( P = 0.045) and TTF ( P = 0.019) decreased from baseline to Week 6 in the HII group. These changes were similar to the left TSF ( P = 0.038) and TTF ( P = 0.011). The changes in the HII group showed a marked decrease at Week 6. 4) There were significant group by time interaction effects in the PT of the left knee extensor ( P = 0.037) and PT of the right knee flexor ( P = 0.012). These results were similar with the WR of the right knee flexor ( P = 0.002) and the WR of the left knee flexor ( P = 0.019) in the HII group, which were significantly higher than those of the other three groups at Week 4 and 6.

WB-EMS administered at high impulse intensity can improve Resistin, body composition including thigh circumference, and isokinetic strength in healthy men after approximately 4 to 6 weeks.

Compensating unstable situations is an important functional capability to maintain joint stability, to compensate perturbations and to prevent (re-)injury. Therefore, reduced maximum strength and altered neuromuscular activity are expected by inducing instability to load test situations. Possible effects are not clear for induced instability during maximum legpress tests in healthy individuals.

To compare isokinetic legpress (LP) strength and lower-leg muscle activity using stable (S) and unstable (UN) footplates.

16 males (28 ± 4 yrs, 179 ± 7 cm, 75 ± 8 kg) performed five maximum LP in concentric (CON) and eccentric (ECC) mode. The maximum force (Fmax) and muscle activity were measured under conditions of S and UN footplates. The tested muscles comprised of the tibialis anterior (TA), peroneus longus (PL) and soleus (SOL) and their activity were quantified against the MVIC of each muscle respectively.

The main finding revealed a significant reduction in Fmax under UN condition: 11.9 ± 11.3% in CON and 23.5 ± 47.8% in ECC ( P < 0.05). Significant findings were also noted regarding the RMS derived values of the EMG of PL and TA.

Unstable LP reduced force generation and increased the activity of PL and TA muscles which confirmed greater neuromuscular effort to compensate instability. This may have some implications for resistance testing and training coupled with an unstable base in the prevention and rehabilitation of injury to the neuromusculoskeletal system.

The purpose of this study was to examine muscle damage and EMG responses during recovery period following exhaustive concentric and eccentric contractions.

Fifteen football players participated in this study. In order to evaluate the recovery period after the muscle damage exercise protocol, the expected damage was provoked by concentric and eccentric contractions. The EMG data obtained from Rectus Femoris muscle and levels of CK, LDH, and Myoglobin analysed from plasma were recorded before, immediately after and post 24 th , 48 th , 72 nd , 168 th hours of the exercise.

Save a significant change in the maximum EMG value of Rectus Femoris muscle, no difference was found among other variables ( p > 0.05). While there was no difference ( p > 0.05) between the base values (PER) accepted as reference of CK, LDH, Myoglobin and levels at other hours after exercise, there was also no difference ( p > 0.05) among values of CK, LDH, Myoglobin between eccentric and concentric contractions.

As a result, various EMG measures and muscle damage responses were recorded during the recovery period after intensive resistance exercises. However the responses during recovery period did not differ by the contraction type.

The purpose of this study was to evaluate changes to key aerobic performance determinants, namely maximal oxygen uptake (VO 2max ), lactate threshold (LT) and gross efficiency (GE) over the cycling season.

Twelve well-trained road cyclists completed three incremental tests during a season in order to determine VO 2max , LT and GE. The laboratory tests were performed using the following sequence: after the transition period (TRAN), during the preparatory period (PREP) and during the competition period (COMP).

VO 2max did not change significantly over the season. Workload at lactate threshold (WL LT ) increased by 11% between the TRAN and COMP periods ( p < 0.001), which was accompanied by an increase in oxygen uptake at lactate threshold (VO 2LT ; p < 0.01). The percentage of VO 2max at the LT changed from 80.1% to 85.6% ( p < 0.05). GE increased from 21.9 ± 1.1% in TRAN to 22.8 ± 0.8% in COMP ( p < 0.01). No significant correlations were found between VO 2max and GE and between changes in GE and those in VO 2max in any training period.

In well-trained athletes, the training process contributes mostly to improvements in submaximal indicators, while it does not change VO 2max . GE is an indicator that is expected to improve over the season, but further research is needed to explain the mechanisms responsible for the individual fluctuations of the GE value in athletes.

The use of unstable training environments has been proposed to enhance the specific effects of movement through an increased activation of stabilizers and core muscles, but not for athletic or sport performance training requiring power.

The purpose of the study was to determine the effects in muscular strength and power outputs after eight weeks of stable and unstable resistance training in physically active subjects with maximal velocity of movement during concentric phase with the load of 50% of 1RM.

Seventy two male recreationally active subjects were divided into three groups (Unstable-UTG, Stable-STG and Control-CG). Unstable and Stable training groups trained twice a week for 8 weeks, bench press and squat exercises, 6 sets of 6 repetitions for each exercise. Pre and post-training measures included 1RM and peak power in stable and unstable conditions for bench press and squat.

The results showed that there was a significant difference in main effects found with the training induced improvement between the training groups in pre- to post-test in squat 1RM, showing the transfer of specific unstable training exercises on 1RM squat. However, this was not the case in 1RM bench press. Both modalities (Stable and Unstable) produced statistically significant ( p < 0.05) training effects on 1RM, with very small increases ranging from 3–7%. Significant main effects for peak power were found for bench press ( p = 0.008) and squat ( p = 0.025) exercises after the experimental program on both testing surfaces (stable and unstable). Both training programs produced greatest power gains on the surface on which the training was performed. The UTG improved significantly ( p < 0.01) on peak power output on both the bench press and squat (12%) on unstable conditions. The STG improved significantly ( p < 0.01) on peak power output on both the bench press and squat (7%) during stable conditions.

The increase of 1RM in previously resistance untrained subjects is lesser than expected. The largest 1RM & peak power increases occurred after squat training on unstable surface, which suggests that unstable surface will not necessarily have negative effects on lower body performance.

Long-term habitual rear-foot strike (RFS) pattern with modern running shoes may negatively affect the intrinsic muscle function of the medial longitudinal arch, which can increase the risk of foot disease.

This study aims to explore whether habitual RFS pattern with modern running shoes can affect the muscle strength of the medial longitudinal arch.

A total of 12 runners who exhibited habitual RFS pattern (RR) with modern running shoes and 12 nonhabitual runners (NR) underwent plantar muscle group strength test for 10 s, hallux flexion and lesser toe flexion strength test. The maximal strength for all tests was normalised by body mass.

No significant differences, on any of the outcome measures, were noted between the two groups. However, in RR the normalized strength of plantar muscle group demonstrated a decreasing trend ( p = 0.065).

Runners who exhibit habitual RFS pattern with modern running shoes present a decreasing trend in the muscle strength of the medial longitudinal arch. The effects of posture and cushioned shoes should be explored further.

Ankle braces are commonly used to protect ankle joints from a sprain by restricting inversion. However, the difference between a soft brace (SB) and a semi-rigid brace (SRB) regarding kinematic and kinetic changes of the lower limb joints after forward and lateral drop landing is unknown.

The aim of this study was to evaluate the effect of SB and SRB, on kinematic and kinetic changes after each drop landing in healthy young women.

Ten female adults were assessed for one leg while wearing SB, SRB or non-brace (NB). For assessing kinematic and kinetic changes after drop landing, the participant jumped and landed forward and laterally with one leg on a force platform. Knee and ankle joint angle and moment, peak ground reaction force (pGRF), time to peak GRF (TpGRF), the rate of force development (RFD) and GRF impulse (impulse) were measured.

The results indicated that knee flexion angle, TpGRF, RFD, and impulse were significantly different between SRB and NB after forward drop landing. SRB demonstrated significant increases in RFD and decreases in impulse.

Semi rigid brace may be beneficial in providing more restriction to the ankle joint for preventing ankle sprains during landing.

Sports competitions are significant sources of psychophysiological stress, especially for young athletes submitted to competitions in a congested match schedule.

In order to verify the effect of short recovery periods (24-hours) in the subsequent match, the response of salivary cortisol (sC) and match intensity were investigated in two successive soccer matches during an official tournament.

Twenty (20) young soccer players (16.8 ± 0.5 years; 172.9 ± 7.7 cm; 65.0 ± 7.9 kg) accepted to participate and 14 completed the 2 matches within a two day-period. Subjects provided saliva samples before and after each match and the session rate of perceived exertion, (session-RPE) method was utilized to define the match intensity.

The sC concentration significantly increased in both matches ( ρ < 0.05), representing an increase of 74% and 112% in matches 1 and 2, respectively. Moreover, the variation was not different between the matches ( ρ > 0.05). There was no variation in match internal load for match 1 to match 2 ( ρ > 0.05). A significant difference was noted between high and low salivary cortisol groups divided a posteriori into both matches (match 1: p < 0.001; ES: 2.7 and match 2: p < 0.001; ES: 2.3).

The findings of this study indicate that the short recovery-time did not influence the sC and match internal load responses in the subsequent match. In addition, athletes with high responsiveness to the stressful demands of the matches tend to maintain this condition regardless of the time on field and the RPE reported.

A number of studies have assessed the effect of kinesiology tape (KT) application with respect to the delayed onset of muscle fatigue.

To determine the effects of direction of KT application on the delayed onset of quadriceps fatigue.

An isokinetic dynamometer was used to induce concentric quadriceps fatigue in 15 healthy participants prior to applying KT. The KT was randomly applied on the muscles in two possible orientations: from origin to insertion or from insertion to origin. After the application the number of repetitions of knee extension required to induce fatigue was recorded.

Regardless of the direction of application, the number of repetitions needed to generate muscle fatigue increased after the KT was applied. On the other hand, there was no significant difference between taping directions.

KT application on the quadriceps delays the onset of its isokinetically-induced fatigue, irrespective of the direction of application. Therefore, using KT may be considered as a possible technique in those tasks where fatigue may seriously hamper performance.

Distal radius fractures are the third most common fracture observed in osteoporotic patients. In addition, wrist muscle weakness may be a risk factor for such fractures because of the protective role these muscles play during falls.

The main objective was to explore isokinetic wrist muscle strength in osteoporotic and matched non-osteoporotic postmenopausal women.

Twenty osteoporotic postmenopausal women (patient group) and 15 healthy non-osteoporotic postmenopausal women with a normal DXA score (control group) were recruited. Bone mineral density was measured using a DXA device. Vertebral (L1–L4), femoral neck, and femoral total measurements were recorded. Wrist muscle strength was evaluated isokinetically.

Peak moment values of the wrist flexors at 60 and 180 ∘ /s were significantly lower in the patient group than in the control group. Extensor muscle strength did not differ significantly between the 2 groups.

Wrist flexors strength is lower in osteoporotic postmenopausal women than their non-osteoporotic counterparts. As this variation might be a risk factor for distal radius fractures in osteoporotic postmenopausal women, strengthening this muscle group should be seriously explored.