Self-selected Condition Research Articles

The application of multilevel modelling to account for the influence of walking speed in gait analysis

Differences in gait performance can be explained by variations in walking speed, which is a major analytical problem. Some investigators have standardised speed during testing, but this can result in an unnatural control of gait characteristics. Other investigators have developed test procedures where participants walking at their self-selected slow, preferred and fast speeds, with computation of gait characteristics at a standardised speed. However, this analysis is dependent upon an overlap in the ranges of gait speed observed within and between participants, and this is difficult to achieve under self-selected conditions. In this report a statistical analysis procedure is introduced that utilises multilevel modelling to analyse data from walking tests at self-selected speeds, without requiring an overlap in the range of speeds observed or the routine use of data transformations.

Sagittal plane trunk posture influences patellofemoral joint stress during running.

Cross-sectional, repeated-measures. Objectives To examine the association between sagittal plane trunk posture and patellofemoral joint (PFJ) stress, and to determine whether modifying sagittal plane trunk posture influences PFJ stress during running. Patellofemoral pain is the most common injury among runners and is thought to be the result of elevated PFJ stress. While sagittal plane trunk posture has been shown to influence tibiofemoral joint mechanics, no study has examined the influence of trunk posture on PFJ kinetics. Twenty-four asymptomatic recreational runners (12 women, 12 men) ran overground at a speed of 3.4 m/s under 3 trunk-posture conditions: self-selected, flexed, and extended. Trunk and knee kinematics, ground reaction forces, and electromyographic signals from selected lower extremity muscles were obtained. A previously described PFJ biomechanical model was used to quantify PFJ stress. The mean ± SD trunk flexion angles under the self-selected, flexed, and extended running conditions were 7.3° ± 3.6°, 14.1° ± 4.8°, and 4.0° ± 3.9°, respectively. A significant inverse relationship was observed between mean trunk flexion angle and peak PFJ stress during the self-selected condition (r = -0.60, P = .002). Peak PFJ stress was significantly lower in the flexed condition (mean ± SD, 20.2 ± 3.4 MPa; P<.001) and significantly higher in the extended condition (23.1 ± 3.4 MPa; P<.001) compared to the self-selected condition (21.5 ± 3.2 MPa). Sagittal plane trunk posture has a significant influence on PFJ kinetics during running. Incorporation of a forward trunk lean may be an effective strategy to reduce PFJ stress during running.

Getting the Balance Right in Intercultural Groups: A Dynamic Social Network Perspective

Problem: A common assumption is that students prefer to select their friends for group-work. The prime goal of this study was to understand the impact of two group selection methods on how students from diverse cultural backgrounds build learning and work relations. Method: Social Network Analysis in a pre-post test manner in a quasi-experimental design of 81 vs. 70 third-year students. Solution: In this study, we “disrupted” this group selection process after Day 1 by balancing students from different parts of the social network together. In one condition the students were “balanced” into groups by staff to encourage structural hole formation, and in the other condition students were allowed to self-select their group members to encourage network closure. Results: Students in the self-selected condition primarily selected their friends from a similar cultural background. In both conditions the learning networks after 11 weeks were primarily predicted by the group allocation and initial friendships. However, students in the balanced condition developed more cross-cultural learning links. These results indicate that teachers can actively intervene in the cross-cultural dynamics in- and outside the classroom.

To Let Students Self-Select or Not

When students can self-select their group members, a common assumption is that students prefer to select friends from similar cultural backgrounds. However, when teachers randomize students in groups from different cultural backgrounds, students are “forced” to work together. The prime goal of this study is to understand the impact of two group selection methods on how students from diverse cultural backgrounds build learning and work relations, using an innovative quantitative method of Social Network Analysis in a pre–post test manner. In a quasi-experimental study of 2 × 69 students, in one condition the students were randomly allocated to groups by staff and in the other, students were allowed to self-select their group members. The results indicate that students in the self-selected condition primarily selected their friends from a similar cultural background. The learning networks after 14 weeks were primarily predicted by the group allocation and initial friendships. However, students in the random condition developed equally strong internal group relations but more “knowledge spillovers” outside their group, indicating that the random condition led to positive effects beyond the group.

Exercise experience influences affective and motivational outcomes of prescribed and self‐selected intensity exercise

The purpose of the study was to compare affective and motivational responses to exercise performed at self-selected and prescribed intensity [close to ventilatory threshold (VT)] between physically active and sedentary women. Following a graded exercise test, the women completed two 30 min bouts of treadmill exercise (on separate days, order counterbalanced). Intensity was prescribed in one session and self-selected in the other. Exercise intensity, exercise-efficacy, perceived competence, autonomy and affective responses were assessed. Results showed that the active women self-selected to exercise at a significantly higher %HR(peak) than their sedentary counterparts but, importantly, both groups exercised close to their VT. The order of conditions influenced affective and motivational responses. The active women experienced more positive affect during exercise and greater competence than sedentary women when the self-selected condition was completed first. Autonomy was higher for the self-selected condition. Self-efficacy and competence were higher in the active women. Differences in self-efficacy perceptions before the exercise depended on which condition was completed first. In conclusion, sedentary women felt relatively positive in the self-selected condition but would benefit from familiarization and experience with exercise to enhance their self-efficacy and competence.

Electromyography and kinematic changes of gait cycle at different cadences in diabetic neuropathic individuals

Changes in gait cadence caused by challenging situations in daily life might induce higher demand for strength and propulsion in diabetic neuropathic (DN) subjects. Forty-six subjects (healthy and DN) walked at two cadences (self-selected and 25% higher). Kinematic and electromyographic data were obtained from lower limbs and compared across the gait cycle. DN subjects showed a delayed peak in plantarflexor activity along the whole cycle (irrespective of cadence) compared with healthy subjects. However, during the imposed cadence, DN individuals showed reduced ankle range of motion along the entire cycle compared with the self-selected condition and healthy individuals walking at both cadences (P = 0.002). These findings suggest that when diabetic individuals face a new challenging situation that induces a higher demand for muscle strength and propulsion, the necessary range of motion and neuromuscular control around distal joints are insufficient.

Psychophysiological Responses During Self-Selected and Prescribed-Intensity Resistance Training in Sedentary Men

PURPOSE: The aim of this study was to examine differences in training load, exertional and affective responses during self-selected and prescribed intensity bouts of resistance exercises in sedentary men. METHODS: Twenty-two participants (age 35.8 ± 5.8 yr; body mass, 81.1 ± 8.7 kg; BMI, 25.5 ± 2.6 kg·m-2), completed an orientation session, one maximal repetition (1RM) testing session, and two experimental trials of resistance exercise bouts at self-selected and prescribed-intensity, which were completed in a counterbalanced order. In the experimental trials, participants performed seven different exercises in using the following order: 1) chest press machine, 2) leg press machine, 3) seated machine rows, 4) seated machine leg extension, 5) seated machine overhead press, 6) seated machine biceps curl, and 7) standing cable triceps extension exercises. In the prescribed-intensity trial, three sets of 10 repetitions of each exercise were performed at 75% of his individual 1RM, whereas in the self-selected intensity subjects were permitted to self-select the load for each set and exercise. Perceived exertion (OMNI-RPE Scale), affective valence (Feeling Scale, Hardy & Rejeski, 1989) and training load (%1RM) of each set and exercise were recorded as the outcome variables. RESULTS: Results of 2 (self-selected vs prescribed-intensity) X 3 (sets) repeated measures multivariate analyses of variance revealed that, at self-selected condition, participants chose a lower exercise load (55.2 ± 3.4% vs 75% of 1RM), had a lower perceived exertion (5.8 ± 1.1 vs 8.5 ± 1.7), and a more pleasant affective response (0.8 ± 0.3 vs -1.2 ± 0.5) compared to an prescribed-intensity condition (p < 0.05). CONCLUSIONS: These findings demonstrate that the training load, perceived exertion, and affective response of self-selected exercises condition differ from prescribed-intensity condition. If the main goal is to increase adherence, a self-selected intensity can promote a more pleasant affective response, which may hopefully lead to a positive memory of the activity, increasing motivation for future physical activity behavior, and thus improving exercise adherence.

Interactive-Virtual Reality (IVR) Exercise: An Examination of In-Task and Pre-to-Post Exercise Affective Changes

In this research, we examine the influence of imposed vs. self-chosen interactive/virtual reality (IVR) exercise on affect response following, as well as during, exercise. Our sample included 131 university students who were assigned to one of three 10-min conditions: (a) self-selected interactive/virtual reality (IVR) exercise, (b) externally imposed IVR exercise, or (c) regular exercise. Exercise intensity was standardized in terms of metabolic benchmarks. Mood benefits were observed pre-to-post exercise regardless of condition. During exercise, however, higher pleasure ratings were reported by participants in the self-selected IVR exercise condition. The implications of the immediate mood effects of self-selected IVR exercise are discussed.

Affective Responses To Resistance Exercise Performed At Self-selected And Imposed Loads In Trained Women.

There is mounting evidence that acute aerobic exercise performed at a self-selected (SS) intensity is rated as being more pleasant and subsequently fosters greater motivation for regular exercise participation when compared to imposed-intensity exercise. However, no research to date has directly addressed either of these contentions with resistance exercise (RE). PURPOSE: The purpose of this investigation was to examine the affective responses to SS and imposed-load bouts of acute RE. Differences in proxy measures of motivation to participate in SS and imposed-load RE were also examined. METHODS: Twenty-one (M age = 23 years) recreationally-trained women completed acute bouts of RE using loads of 40% of one repetition maximum (1RM), 70% of 1RM, and a self-selected (SS) load. RE consisted of 3 sets of 10 repetitions of 4 different strength training exercises. Global ratings of pleasure were assessed prior to, during, and following each RE condition using the Feeling Scale (FS). Self-efficacy (SE) and intention (INT) for regular participation in RE using 40%1RM, 70%1RM, and SS loads during the next month were also assessed post-exercise. RESULTS: Results of repeated measures ANOVA analyses revealed significant increases in the FS during (p < 0.01) and following (p < 0.01) the 40% and SS Conditions and following (p < 0.01) the 70% 1RM Condition. Conversely, a significant decrease in the FS (p < 0.01) emerged during RE performed at 70% 1RM. Univariate analyses also revealed that the SS condition was associated with the highest ratings of SE and INT for future RE participation (p < 0.05). CONCLUSIONS: The present results suggest that SS and imposed load bouts of RE are associated with different trajectories of affective responses during and following exercise. Additionally, despite experiencing similar affective benefits following each bout of RE, women reported greater SE and INT to participate in RE using a SS load. The differences in FS, SE, and INT responses accompanying SS and imposed-load bouts of RE observed in this investigation may have valuable practical implications for RE prescription.

Perceived Exertion During Acute Resistance Exercise Performed At Self-selected And Imposed Loads In Trained Women

Previous research has demonstrated that untrained women report significantly lower ratings of perceived exertion (RPE) during self-selected (SS) load bouts of acute resistance exercise (RE) when compared to sessions performed using typically imposed RE loads. However, the extent to which RPE responses differ between SS and imposed-load bouts of acute RE among trained women remains unclear. PURPOSE: The purpose of this investigation was to examine RPE responses to self-selected and imposed-load bouts of acute RE in a sample of trained women. METHODS: Twenty-one (M age = 23 years) recreationally-trained women completed acute bouts of RE using loads of 40% of one repetition maximum (1RM), 70% of 1RM, and a self-selected (SS) load. RE consisted of 3 sets of 10 repetitions for each of the leg extension (LE), leg curl (LC), lat pull-down (LPD), and chest press (CP) exercises. Assessments of RPE were obtained immediately after each set during the 3 RE conditions. RESULTS: Results of separate 3 (Condition) × 3 (Set) repeated measures ANOVAs yielded significant main effects for Condition (p < 0.01) and Set (p < 0.01) for each exercise and significant Condition × Set interactions (p < 0.05) for both the LPD and CP exercises. Post-hoc analyses revealed that RPE increased from Set 1 to Set 3 for the CP and LPD exercises in both the 70% 1RM and SS conditions but did not increase across sets in the 40% condition. RPE were also found to be significantly higher in the 70% condition relative to the SS or 40% conditions and RPE reported during SS condition were higher when compared to the 40% condition for all exercises. CONCLUSIONS: The present results suggest that RPE reported during SS bouts of RE differ significantly from RPE observed during imposed-load bouts of RE. Although evidence addressing RPE responses to acute RE remains limited, effort sense experienced during acute RE may serve as a salient determinant of the adoption and maintenance of regular RE behavior. Accordingly, the differences in RPE during acute RE observed in the present investigation may have valuable practical implications for the prescription of RE participation.

The psychological and physiological responses of sedentary individuals to prescribed and preferred intensity exercise

Affective valence responses to exercise may influence adherence. According to a newly proposed dual-mode model, affective responses have been proposed to vary depending on whether exercise is undertaken above or below the anaerobic threshold. With the model in mind, the study objectives were to explore the impact of an above-lactate, below-lactate, and self-selected exercise condition on acute affective responses in sedentary individuals. Using a repeated measures design, 12 volunteers participated in two prescribed intensity exercise conditions (above and below-lactate threshold) and one self-selected intensity exercise condition. The three conditions were randomized. An incremental walking protocol was used to identify exercise intensities that would elicit above- and below-lactate threshold work rates for each participant. The exercise conditions were completed on different days and each lasted for 20 minutes. Physiological and affective responses were recorded pre-exercise, during exercise, and post-exercise. Affective responses were more negative in the above-lactate condition during exercise compared with the below-lactate and self-selected conditions. There were no differences between the conditions post-exercise. Participants exercised around the lactate threshold and at a significantly higher intensity in the self-selected compared with the below-lactate condition. Inter-individual variability in responses was greatest below the lactate threshold, with similar levels of variability in the self-selected and above-lactate conditions. Data are consistent with the proposals of the dual-mode model and support the use of self-selected intensity with sedentary individuals to promote positive affective responses.

How Does the Heel-Off Posture Modify Gait Initiation Parameter Programming?

The authors studied the adjustment of the 2 distinct known expressions of gait velocity, the velocity of the center of gravity (CG) and the velocity of the center of foot pressure (CP) at the end of the 1st step in 2 experimental situations: natural gait initiation (the control situation, CS) and heel-off gait initiation (the test situation, TS). Gait was initiated by 7 healthy participants, from an erect spontaneous posture in the CS and from a posture with heels raised in the TS, on a force platform at 3 self-selected speed conditions. Biomechanical data from the force platform were collected in both experimental situations, and the authors used a particular gait analysis based on the differential method of Y. Brenière (2003) in order to approach velocity modulation by means of step length and frequency. Results showed that CG and CP velocities were adjusted differently during heel-off gait initiation than during natural gait initiation. CP velocity, as compared with CG velocity, was overestimated in TS. Results also established the relevance of the expression of step velocity by means of step length and frequency: The central nervous system, taking into account the specific postural constraints of each experimental situation, uses a reference value and a regulating parameter to modulate step velocity. Moreover, the contributions of 1st step length and frequency to the expression of step velocity in TS and CS were different. Thus, a specific locomotor behavior corresponds to a given experimental situation that is characterized by its own initial biomechanical constraints.

An Approach to Studying Circadian Rhythms of Adolescent Humans

The "long nights" protocol was designed to evaluate sleep processes and circadian rhythm parameters in young humans. A total of 19 children (10 boys, ages 11.2 to 14.1 years [mean = 12.7 +/- 1.0], and 9 girls, ages 12.2 to 14.4 years [mean = 13.1 +/- 0.7]) took part in the study. Sleep/wake initially was assessed at home using actigraphy and diary for 1 week on each child's self-selected schedule followed by an 8-night fixed light-dark (LD) condition, while sleeping from 22:00 to 08:00 h and wearing an eye mask to exclude as much light as possible. Phase measurements included 4-night mean actigraphically estimated sleep onset and offset as well as 1-night dim light salivary melatonin onset (DLSMO) phase at the end of each condition. Subjects then lived in the laboratory for 6 consecutive cycles: Day 1 LD = 14:10 h, lights out 22:00 to 08:00 h; Days 2-4 LD = 6:18 h, lights out 18:00 to 12:00 h; Days 5-6 = constant routine in continuous dim light (about 20 lux); Night 6 = 14 h recovery sleep. Phase markers (sleep onset, sleep offset, DLSMO) were significantly less dispersed after the fixed LD as compared to the self-selected condition, indicating efficacy of the LD protocol. Phase markers were correlated at the self-selected assessment (sleep onset vs. sleep offset r = .72; DLSMO vs. sleep onset r = .82; DLSMO vs. sleep offset r = .76) but not on the fixed schedule, probably due to restricted range. The constant routine provided additional phase markers, melatonin offset and midphase. Offset phase of melatonin secretion was significantly correlated with age (r = .62) and Tanner stage (r = .62). In conclusion, these preliminary data indicate a relationship between adolescent development and circadian phase. Thus, the long nights protocol is a feasible way in which to assess circadian parameters in young humans as well as to examine intrinsic sleep processes.

Imperfect Price Discrimination and Variety

In many environments a monopolist can price discriminate even though consumers can select any option offered by the firm. Though consumers seem indistinguishable to the firm, the monopolist can discriminate by exploiting its knowledge of the joint distribution of agents' characteristics (in this paper, locations and reservation prices) to offer the most profitable menu of alternatives given the constraints imposed by the maximizing behavior of each type of consumer (see Chiang and Spatt [1982] for a partial bibliography of this research). In many of these models consumers agree typically on the definition of the best available good (exceptions include Adams and Yellin [1976] and Telser [1979]) but disagree on their incremental valuation of quality. The consumer's selection of a price-quality contract from the set offered by the monopolist can elicit information that the monopolist endogenously exploits. For example, the price-discriminating monopolist may charge a steeper price-quality gradient than predicted by cost considerations (see Mussa and Rosen 1978). In a spatial market the monopolist can discriminate on the basis of differences in cost of travel or location of consumers. I analyze a model I analyze by geometric techniques a spatial model in which a monopolist uses location differences across consumers to price discriminate. The model is used to examine price discrimination in a model of variety in a setting in which consumers disagree on the definition of quality. The full burden of separation of types is not on binding self-selection conditions. Examples are presented in the paper to show the ambiguous output and welfare comparisons between imperfect discrimination and singleprice monopoly. At various extremes discrimination can either (relative to single-price monopoly) make some consumers better off and none worse off, while raising firm profit, or, alternatively, reduce firm output. The effect of an increase in the cost of travel on output, variety, and consumer surplus is demonstrated. The implications of the model are also shown to be exhaustive under various assumptions about the set of observables. X An earlier version of this paper was presented at the NBER-NSF Conference on Hierarchies, Monitoring, and the Nature of the Firm, at the University of Minnesota, Minneapolis, December 1980. 1 gratefully acknowledge the helpful comments of the referee and support from National Science Foundation grant SES-8015086.

EFFECT OF DEOXYCORTICOSTERONE ON SODIUM APPETITE OF INTACT AND ADRENALECTOMIZED RATS.

The effect of DOC on sodium chloride (saline) intake was studied in intact and adrenalectomized rats under "two-bottle" self-selection conditions. It was found that in adrenalectomized rats low doses of DOC produced a decrease in saline intake (restoration of sodium-retaining ability), whereas high doses produced an increase in saline intake (stimulation of sodium appetite). At high doses, however, intact rats consumed more saline and manifested a greater preference for it than did similarly treated adrenalectomized rats. Treatment with corticosterone increased both absolute saline intake and saline preference of DOC-treated adrenalectomized rats.

Effect of Some Self-Selection Conditions on the Voluntary Alcohol Intake of Rats

Effect of Some Self-Selection Conditions on the Voluntary Alcohol Intake of Rats