Isokinetics and Exercise Science

This prospective study evaluated the muscle strength recovery during a two year follow-up, assessed the relationship between different funtional outcome measurements and compared the outcome between younger( $<$ 25 years) and older ( $\geq$ 25 years) patients. Progress in isokinetic muscle performance was measured at all follow-up intervals up to two years postoperatively. The Cincinnati functional score showed significant improvement between all follow-up intervals. Correlation analysis showed a significant relationship between the patients' subjective assessment of knee function and muscle strength and the triple jump test. The older age group had a significant slower recovery than the younger group up to one year postoperatively.

The purpose of this study was to determine the differences between iEMG activity of the medial head (MH) and lateral head (LH) of the gastrocnemius of normal right legs during partial weight bearing isometric plantarflexion contractions under varying percentages of body weight (BW) and maximal contractions. Fifty-three healthy volunteers ranging in age from 18 to 35, with no history of right lower extremity injury or disease volunteered for this study. Each subject's age, height, weight, and medical history were recorded. A chronaximeter was used to identify the motor points of the MH and LH. After performing a 5-minute warm-up, surface electrodes were placed just distal to the motor point, and subjects were positioned on the sliding board of the Total Gym Therapy System. The percentage of BW used as resistance was determined by the angle of inclination of the slide board. The subjects were then directed to plantarflex to 20 degrees, with 8 second iEMG recordings, with a proprioceptive cue, under four conditions: 30%, isometric (1 trial). Paired $t$ -tests concluded the MH consistently demonstrated a larger percent of total iEMG activity than the LH in the 30, 50, and 70% difference between iEMG activity of the MH and LH during the maximum isometric trial was not statistically significant ( $p=$ 0.2958). A repeated measures ANOVA and post-hoc analysis demonstrated the percent of total iEMG differences to be greater at the lighter loads (D30 $>$ D50 $>$ D70; $p<$ 0.0001). These findings strongly suggest separate but complementary functions of the two heads of the gastrocnemius muscle.

The purpose of the current study was to establish that the measurements taken during dynamic contractions could provide insight into differences/similarities that evolve between muscle mechanics and it's neuromuscular (electrical) source as one aging. The present study assesses the differences in strength that is resistance to fatigue (RTF) of the knee extensors (vastus lateralis (VL) and vastus medialis(VM)) as a function of age and gender. Eighty subjects (45 males and 35 females) with a-symptomatic knees were tested; Males: Group A, 20--29 years old ( $N=20$ ); Group B, 30--39 years old ( $N=8$ ); Group C, 40--49 years old( $N=9$ ); Group D, 50--60 years old ( $N=8$ ) and the Females: Group E, 20--39 years old ( $N=25$ ); Group F, 40--60 years old ( $N=10$ ).

All subjects were tested for their dominant knee extensor strength by performing a maximal voluntary isometric contraction (MVIC) and fatiguing bouts at four isokinetic velocities of 300 $^{\circ}$ /sec, 180 $^{\circ}$ /sec, 60 $^{\circ}$ /sec, 30 $^{\circ}$ /sec. The muscular fatigue was assessed by comparing the median frequency (MF) of the surface EMG (SEMG) activity of VL and VM during the 2nd contraction and the 20th (last) contraction of the bouts.

The results showed distinct differences between groups A, B and C, D similarly between group E and F in muscle strength, when performing isokinetic concentric contraction. There was no age and gender difference in isokinetic fatigue ratio (IFR) and in electromyographic measurements in MF of VM and VL. The decrease in knee extensor strength occurred in the 4th decade for the males and in the 3rd for the females.

These results of this study provide quantitative evaluation of knee strength of sedentary adults at various ages. The knowledge of the critical age group allow us to construct a fast, reliable and valid test in assessing the condition of main anti-gravity muscles and alert the person before any stability deficiencies may crop out. The isokinetic findings were in line with the SEMG findings that is the phasic (strength) component of knee extensors decreased with age while there is no significant difference in tonic(endurance) component up to 60 years old. It is anticipated that the proposed protocol as administered may be useful in occupational settings.

{\it Purpose:} The purpose of this study was to assess the effect of varying the measurement axis of the subject relative to an isokinetic dynamometer on the peak flexion and extension moment of the trunk. The effect of testing position (sitting or standing) on peak moment was also investigated.{\it Methods:} Thirty healthy young subjects [8 male, 22 female] were selected at random from a pool of 90 volunteers and asked to perform concentric sagittal flexion-extension cycles at velocities of 60 deg/s, 120 deg/s and 180 deg/s in both the seated and standing position with respect to 5 measurement axes. The subjects were initially aligned with the highest point on the iliac crest(reference axis) and then aligned with 4 measurement axes displaced from the reference axis (25∼mm anterior/posterior and 50mm superior/inferior). {\it Results:} Two-way repeated measures ANOVA revealed significant differences($\alpha < 0.05$) between peak moments recorded between axes and velocity for flexion and extension, however no difference with respect to testing position, i.e., sitting versus standing. Post hoc multiple comparison tests by the Scheff?method revealed that all measurement axes tested were statistically different [$P < 0.001$] from the reference axis, however there were no differences between the two inferior axes [$P = 0.999$] and the two superior axes [$P = 0.982$]. The inferior measurement axes consistently produced greater peak moments than the reference axis while the superior axes consistently produced lower peak moments than the reference axis. Males produced significantly greater peak moments than did females [$P = 0.000$]. {\it Conclusions:} Measurement axis alignment significantly effects the peak moment recorded. Furthermore, these results reinforce the need for accurate and consistent alignment between the subject and the dynamometer. The position of the subject [seated/standing] did not significantly affect the measured peak moment when using the Lido Active Back System in this study.

A variety of isokinetic fatigue protocols have been previously reported in the literature. The purpose of this study was to examine a new protocol to objectively quantify dynamic concentric and eccentric muscle performance in individuals, or in a multiple subject group, under conditions of acute exhaustive exercise. Pre-fatigue maximal peak torque (PT) and peri-fatigue PT values were measured in unilateral dominant leg quadriceps femoris of human subjects using an isokinetic dynamometer. The protocol was based on single-velocity (90 $^{\circ}$ /s) reciprocal-mode concentric/eccentric (CON/ECC) contractions fixed at 35 repetitions per set. A novel ``Fatigue Resistance Index'' (FRI) was then calculated for each individual subject for both CON and ECC contractions. The group CON FRI( $36.5 \pm 3.9$ % maximal force) was greater than group ECC FRI( $26.9 \pm 2.7$ % force). This protocol and FRI permit comparisons between eccentric and concentric dynamic anaerobic muscle performances for a given individual subject, or for a group of subjects.

The purpose of this study was to determine the effects of cryotherapy on isokinetic ankle strength immediately after ice immersion treatment. Concentric (CON) and eccentric (ECC) isokinetic ankle strength was measured on 20 male subjects using a Kin Com 125 AP (Chattanooga Group, Hixson, TN) isokinetic dynamometer. Plantar flexion, dorsiflexion, inversion and eversion motions were assessed at speeds of 60 $^{\circ}$ /s and 120 $^{\circ}$ /s before and immediately after an ice immersion treatment (10 $^{\circ}$ C for 20 $'$ ). Peak torque (PT) values were extracted from the maximal torque curves and used in the data analysis. ECC PT was higher than CON PT at both speeds and was not affected by ice immersion treatment. The only notable finding was a significant main effect for test (PRE vs. POST) for CON dorsiflexion ankle strength. The Tukey post hoc test determined that POST test PT values ( $39.7\pm 12.7$ Nm) were significantly lower than PRE test scores( $45.9\pm 11.2$ Nm). This finding suggests that CON dorsiflexion strength in the ankle may be adversely affected immediately after ice immersion application. Clinicians should still exercise caution when allowing athletes to return to competition immediately following ice immersion application to the lower leg.

Eleven adult males (mean $\pm$ SD age $= 22 \pm 3$ years) performed maximal, concentric isokinetic leg extension muscle actions at velocities of 60, 120, 180, 240, and 300 $^{\circ}\cdot$ s $^{-1}$ on a Cybex 6000 dynamometer. The results indicated that peak torque (PT) decreased( $p<0.05$ ) as muscle action velocity increased. Mechanomyographic (MMG) amplitude increased with velocity to 180 $^{\circ}\cdot$ s $^{-1}$ for each muscle tested (vastus lateralis $=$ VL, rectus femoris $=$ RF, and vastus medialis $=$ VM). For the VL, MMG amplitude continued to increase to 240 $^{\circ}\cdot$ s $^{-1}$ and then plateaued, while the RF plateaued from 180 to 300 $^{\circ}\cdot$ s $^{-1}$ . The VM showed a constant increase in MMG amplitude to 300 $^{\circ}\cdot$ s $^{-1}$ . Electromyographic(EMG) amplitude increased to 180 $^{\circ}\cdot$ s $^{-1}$ and then plateaued for each muscle. These findings indicated muscle-specific differences in MMG amplitude patterns across velocity that may be attributable to differences in fiber type composition, muscle architecture, and/or tissue layer composition. Furthermore, these results suggested that there were muscle-specific, velocity-related differences in the association between motor unit activation(EMG) and the mechanical aspects of muscular activity (MMG).