J. W. Yates

The effects of fish oil and isoflavones on delayed onset muscle soreness.

INTRODUCTION/PURPOSE Fish oils (FO) have been shown to modulate the inflammatory response through alteration of the eicosanoid pathway. Isoflavones (ISO) appear to reduce the inflammatory pathway through their role as a tyrosine kinase inhibitor. Delayed onset muscle soreness (DOMS) develops after intense exercise and has been associated with an inflammatory response. Therefore, we hypothesized that physical parameters associated with DOMS could be decreased via the modulation of the inflammatory response by supplementing subjects with either FO or ISO. METHODS 22 subjects were recruited and randomly assigned to one of three treatment groups: FO (1.8 g of omega-3 fatty acids x d(-1)), ISO (120 mg soy isolate x d(-1)), or placebo (PL) (Western fat blend and/or wheat flour). All treatment groups received 100-IU vitamin E x d(-1) to minimize lipid peroxidation of more highly unsaturated fatty acids. Subjects were supplemented 30 d before the exercise and during the week of testing and were instructed to refrain from unusual exercise. DOMS was induced by 50 maximal isokinetic eccentric elbow flexion contractions. Strength parameters, pain, arm circumference, and relaxed arm angle (RANG) were measured at 48, 72, and 168 h post exercise. Cortisol, creatine kinase (CK), interleukin-6 (IL-6), tumor necrosis factor (TNFalpha), malondialdehyde (MDA), and serum iron were measured before supplementation, after supplementation, and post exercise. RESULTS Significant decreases were observed in RANG and strength 48 h postexercise among all groups, and there were significant increases in pain and arm circumference. There were no significant changes among all groups from baseline at 168 h (7 d) post exercise. There were no significant treatment effects between groups for the physical parameters or for cortisol, CK, IL-6, TNFalpha, MDA, or serum iron. CONCLUSION These data indicate FO or ISO, at the doses supplemented, were not effective in ameliorating DOMS with the above-cited protocol.

Reliability of the psychophysical approach to manual lifting of liquids by females

The psychophysical method for setting lifting standards was evaluated by having seven, female college students lift at four diiferent frequencies (1, 3, 6 and 12 lifts min−1). Only one lifting session was performed in a 24 hour period. During the 4 hour lifting task, subjects were asked to select the amount of water that they believed they could lift comfortably for 8 hours. Subjects were encouraged to make as many weight changes as they needed. Each time the weight was changed the carton was weighed and the time was recorded. At 15 min intervals, subjects were asked about their degree of confidence (DOC) that the current weight was the maximum acceptable one for an 8 hour shift. Oxygen consumption was measured at 30,120 and 240 min of the task. The weights chosen by the subjects at 30 min did not differ significantly from the 4 hour values for frequencies of 1, 3 and 6 lifts min−1. However, at 12 lifts min−1 the weight decreased with time such that the 4 hour value was 23% lower than the weight chosen af...

A Comparison of Peak and Constant Angle Torque-Velocity Curves in Fast and Slow-Twitch Populations

SummaryPeak and constant angle torque-velocity (T-V) curves were measured on a group of fast-twitch (FT,n=10) and slow-twitch (ST,n=6) subjects using a Cybex dynamometer. The T-V curve was plotted from 10 randomly assigned velocities ranging from 0.52 to 5.24 rad s−1 (30 to 300‡ s−1). Each subject was tested four times with at least 24 h between testing sessions. Torque-velocity curves were plotted from the peak torque generated throughout the range of motion and from torque produced at a constant angle (150‡). When all subjects were combined into a single group, no significant difference existed between the normalized T-V curves even though they differed significantly in absolute amounts. When subjects were grouped according to muscle fiber type the T-V curves produced from constant angle torque differed significantly while those generated from peak torque did not. This finding suggests that T-V curves generated from peak torque are not as sensitive to influences produced by muscle fiber type as those curves generated from constant angle torque.

Discriminability of load heaviness: implications for the psychophysical approach to manual lifting

The main objective of this study was to investigate human ability to discriminate between different levels of load heaviness in manual lifting. Twelve male college students participated in the laboratory experiment. Twenty-eight sequences of five boxes that weighed from 5 to 64 lbs (2.27-29.1 kg) were used. The subjects were asked to arrange boxes in each sequence in order of the perceived (increasing or decreasing) heaviness, i.e., from lightest to the heaviest box, or from heaviest to the lightest box. The subjects were also asked to assign linguistic descriptors of perceived load heaviness to each box in the sequence, and to indicate the confidence levels regarding correctness of the assigned box order and assignment of linguistic values. The independent variables included magnitude of weight and load differential between the successive weights in a sequence. The number of sequential ordering errors, assignment of linguistic variables, and estimated confidence levels were highly dependent on the load differential and weight range. It was concluded that in order to assure reliable results of the psychophysical approach to determining the values of maximum acceptable weight of lift, the adjustment process for male subjects should require using small weights of at least 4 lbs (1.8 kg) to be added or removed from the lifted box. The results of this study also suggest that the error rate in load discriminability can be controlled below the 10% level, if the relative difference in weight between successive boxes lifted is at least 12%. Given the above findings, it is suggested that usefulness of some of the recommendations for setting safe limits for manual lifting tasks, which were reached based on the psychophysical approach and broadly reported in the past, may need to be carefully re-examined. Finally, this study showed that the Weber fraction for load heaviness over the range of lifted weights from 8.6 to 29.1 kg is between 0.03 and 0.04.

Moderate static stretching and torque production of the knee flexors.

Winke, MR, Jones, NB, Berger, CG, and Yates, JW. Moderate static stretching and torque production of the knee flexors. J Strength Cond Res 24(3): 706-710, 2010-Recent studies have suggested that acute static stretching (SS) decreases muscular strength and performance, particularly of the knee extensors. The purpose of this study was to investigate the effect of SS on peak concentric and eccentric torque production in the knee flexors. Subjects (13 women and 16 men) were tested for isokinetic concentric (CON) and eccentric (ECC) peak torque at 2 velocities (60 and 210°·s−1) before and after a 3-minute knee flexor SS protocol. Subjects also underwent a control day in which the isokinetic pre- and posttests were separated by 10 minutes of sitting rather than stretching. A sit and reach test was administered on both days to assess changes in flexibility that occurred as a result of the stretching or control protocols. The change in flexibility was significantly greater after stretching than after sitting. Changes in peak torque were not significantly different between the stretching and control conditions for either velocity or contraction type. Compared with the control condition, SS of the knee flexors before maximal isokinetic testing does not lead to significantly diminished CON or ECC torque output at slow or fast contraction velocities. These data suggest that moderate SS does not impact the performance of all muscle groups.

An electromyographic analysis of seated and standing lifting tasks.

The objective of this project was to compare the muscular effort exerted during manual lifting tasks performed in standing versus seated posture. Six male undergraduate and graduate students performed 12 different static and dynamic lifts in both sitting and standing positions. During each effort electromyographic (EMG) data were collected on four muscles groups (low back, upper back, shoulder, and abdominals). Four contractions were designed to elicit maximum muscular effort in the four groups being monitored. The remaining data were then expressed as a percentage of maximum EMG. Each subject performed the following: maximum static lift when sitting; maximum static lift when standing; sitting, static lift with 15.9 kg; standing, static lift with 15.9 kg; dynamic sit-forward lift with 15.9 kg, dynamic stand-forward lift with 15.9 kg, dynamic sit-twist with 15.9 kg, dynamic stand-vertical lift with 15.9 kg. Each of the lifts was performed with a wooden tray with slotted handles. Root mean square (RMS) values of the EMG data were calculated for three second periods. EMG activity in the low back, upper back, and shoulder was greater during sitting lifting than during standing lifting. The sit-twist lift resulted in the highest EMG in the abdominal muscles. Dynamic lifts resulted in more muscle activity than did static lifts. From these data it was concluded that sitting-lifting results in greater stress in the low back, upper back, and shoulders than does lifting while standing.

Recovery of dynamic muscular endurance

SummaryRecovery of the rate of dynamic muscular endurance was measured in two groups of college-aged males. Subjects were required to perform elbow flexion (between the angles of 70 and 170 degrees) for as long as possible at the rate of 38 contractions/min while loaded with 1/6 of their maximum isometric strength (MVC). The task was terminated when the subject fell four contractions behind the required cadence or failed to complete two successive contractions. Subsequent to the task the subject was given a predetermined rest period after which a second fatigue bout to failure was performed. The rest intervals for Gp I (n=22) were 5, 15, 45, 135, 405, and 1215 seconds, while the rest intervals for Gp II (n=17) were 10, 30, 90, 270, 810, and 2550 s. Each subject completed six recovery intervals with the order of administration assigned at random. The percentage of recovery was calculated by dividing the exercise time of the first bout into the time of the second bout. These normalized data for the two groups were combined for analysis providing a 12 point recovery curve. The percentage of recovery ranged from 15.4% after 5 s to 91.8% after 2550 s. Analysis of the data revealed that the recovery pattern of dynamic muscular endurance progressed very rapidly initially, reached 50% at approximately 2 min and 15 s and was slightly less than 90% complete at 20 min. Exponential analysis of these data yielded a three-component curve.

The Effect of Time in the Psychophysical Study of the Maximum Acceptable Amounts of Liquid Lifted by Females

The determination of the maximum acceptable weight of lifting using the psychophysical method was examined over a four hour period. Six females lifted a standard milk carton case from the floor to a height of 0.79 m. The subjects chose the amounts of liquid acceptable to them by instructing a helper to increase or decrease the weight of the case. The amount of liquid acceptable to subjects at 4 lifts/min after four hours of lifting was not different from the weight estimated by them after 20 minutes. However, at 8 lifts/min the acceptable amount of liquid decreased with time. These results suggest that a 20 minute period may be sufficient to estimate the maximum acceptable weight for the frequency of 4 lifts/min, but not for the frequency of 8 lifts/min.

Who Needs a Bag

In this issue of Medicine & Science in Sports & Exercise®, Hopker et al. (4) report on the reliability of gross efficiency as measured using the Douglas bag technique (3) (often miscited), finding a total within-subject variation of 1.5%. This excellent reliability is considerably bette

Weight Discriminability and Subjective Assessment of Load Heaviness: A Pilot Study

The main objectives of this pilot study were to investigate human ability to: 1) estimate weight of boxes on a lifting task, 2) discriminate among different levels of load, and 3) relate this ability to subjective perception of load heaviness expressed in terms of linguistic descriptors. The effects of color and load differential, defined as a constant weight difference among a series of five boxes, on perception of load heaviness, were also studied. It was shown that the human ability to discriminate among weights of boxes lifted is severely impaired as the load differential decreases below 4 lbs. In addition, as weight of the box exceeds 30 lbs., the difficulty in load differentiation and load estimation, as measured by the number of errors made, significantly increases. This study also suggests that the use of linguistic (verbal) descriptors in the estimation of weights of boxes lifted from the floor to table height, allows for better judgement than the use of numerical values alone.