Do Individual Responses to Resistance Exercise Exist to an Extent That Can be Detected Beyond That of Measurement Error/Random Biological Variability?

Millions of dollars are spent analyzing inter-individual differences in response to resistance exercise, but the lack of a non-exercise control group means they may simply be examining random error. The purpose of this study was to determine whether there are inter-individual differences in response to two distinct resistance exercise protocols. Participants (n=151) were randomly assigned to one of 3 groups as follows: (1) a traditional exercise group performing 4 sets to failure with a load that could be lifted 8-12 times; (2) a one-repetition maximum (1RM) training group performing a 1RM test each visit; and (3) a non-exercise control group. Both exercise groups performed 18 sessions of elbow flexion exercise over 6 weeks. Both 1RM training (2.3kg) and traditional training (2.4kg) increased 1RM strength to a similar extent. Only the 1RM group increased untrained arm 1RM strength (1.5kg) which was greater than both other groups (p\u3c0.05). The traditional exercise group also increased ultrasound measured muscle size at all sites (all\u3e0.22cm), each of which were greater than both the control and 1RM group (p\u3c0.05). The 1RM group did not increase muscle mass (p\u3e0.05). Across both training groups, the only individual responses were found in the change in 1RM strength of the trained arm in the traditional training group (Levene’s test p\u3c0.05) in which 10 individuals (25%) were classified as responding differently from the mean. The variability in the response to other outcomes did not exceed that of the control group indicating it could not be detected above random error. Other commonly used approaches of classifying differential responders such as clustering analyses, standard deviations above and below the mean, and upper/lower percentiles would produce different results but are not appropriate. These findings demonstrate the importance oftaking into consideration the magnitude of random error when classifying individual responders, and provide possible rationale as to why numerous analyses fail to find/replicate what genes may be responsible for producing more favorable exercise outcomes

The association of handgrip strength and mortality: What does it tell us and what can we do with it?

© Copyright 2019, Mary Ann Liebert, Inc., publishers 2019. The relationship between grip strength and mortality is often used to underscore the importance of resistance exercise in physical activity guidelines. However, grip strength does not appear to appreciably change following traditional resistance training. Thus, grip strength could be considered reflective of strength independent of resistance exercise. If true, grip strength is not necessarily informing us of the importance of resistance exercise as an adult, but potentially highlighting inherent differences between individuals who are stronger at baseline compared to their weaker counterpart. The purpose of this article is to discuss: (1) potential factors that may influence grip strength and (2) hypothesize strategies that may be able to influence grip strength and ultimately attain a higher baseline level of strength. Although there appears to be a limited ability to augment grip strength as an adult, there may be critical periods during growth/development during which individuals can establish a higher baseline. Establishing a high baseline of strength earlier in life may have long-term implications related to mortality and disease

The Measurement of Strength in Children: Is the Peak Value Truly Maximal?

It is unclear whether the measurement of maximum muscle strength in younger children can be performed accurately due to factors such as motivation and maturity (i.e., the ability to receive instruction). If there is a large change in a ratio between muscular strength and size from the youngest to the oldest, then this might provide some indication that the youngest may not have been able to voluntarily activate their muscles for reasons mentioned previously. The purpose of this study was to observe the ratio between handgrip strength (HGS) and forearm muscle thickness (MT) across differing ages in younger children. A total of 1133 preschool children (559 boys and 574 girls) between the ages of 4.5 and 6.5 years had MT and HGS measurements and calculated the ratio of HGS/MT (kg/cm). Linear regression was used to assess the impact of age and sex on the dependent variables of MT, HGS, and the HGS/MT ratio. The HGS/MT ratio increases moderately from age 4.5 to 6.5 in both boys and girls. However, the difference in this ratio was small between the age ranges in this sample. Our results indicate children as young as 4.5 may be accurately measured with the handgrip strength test

The Perceived Tightness Scale Does Not Provide Reliable Estimates of Blood Flow Restriction Pressure.

CONTEXT: The perceived tightness scale is suggested to be an effective method for setting subocclusive pressures with practical blood flow restriction. However, the reliability of this scale is unknown and is important as the reliability will ultimately dictate the usefulness of this method. OBJECTIVE: To determine the reliability of the perceived tightness scale and investigate if the reliability differs by sex. DESIGN: Within-participant, repeated-measures. SETTING: University laboratory. PARTICIPANTS: Twenty-four participants (12 men and 12 women) were tested over 3 days. MAIN OUTCOME MEASURES: Arterial occlusion pressure (AOP) and the pressure at which the participants rated a 7 out of 10 on the perceived tightness scale in the upper arm and upper leg. RESULTS: The percentage coefficient of variation for the measurement was approximately 12%, with no effect of sex in the upper (median δ [95% credible interval]: 0.016 [-0.741, 0.752]) or lower body (median δ [95% credible interval]: 0.266 [-0.396, 0.999]). This would produce an overestimation/underestimation of ∼25% from the mean perceived pressure in the upper body and ∼20% in the lower body. Participants rated pressures above their AOP for the upper body and below for the lower body. At the group level, there were differences in participants\u27 ratings for their relative AOP (7 out of 10) between day 1 and days 2 and 3 for the lower body, but no differences between sexes for the upper or lower body. CONCLUSIONS: The use of the perceived tightness scale does not provide reliable estimates of relative pressures over multiple visits. This method resulted in a wide range of relative AOPs within the same individual across days. This may preclude the use of this scale to set the pressure for those implementing practical blood flow restriction in the laboratory, gym, or clinic

The perceived tightness scale does not provide reliable estimates of blood flow restriction pressure

© 2020 Human Kinetics, Inc. Context: The perceived tightness scale is suggested to be an effective method for setting subocclusive pressures with practical blood flow restriction. However, the reliability of this scale is unknown and is important as the reliability will ultimately dictate the usefulness of this method. Objective: To determine the reliability of the perceived tightness scale and investigate if the reliability differs by sex. Design: Within-participant, repeated-measures. Setting: University laboratory. Participants: Twenty-four participants (12 men and 12 women) were tested over 3 days. Main Outcome Measures: Arterial occlusion pressure (AOP) and the pressure at which the participants rated a 7 out of 10 on the perceived tightness scale in the upper arm and upper leg. Results: The percentage coefficient of variation for the measurement was approximately 12%, with no effect of sex in the upper (median δ [95% credible interval]: 0.016 [-0.741, 0.752]) or lower body (median δ [95% credible interval]: 0.266 [-0.396, 0.999]). This would produce an overestimation/underestimation of ∼25% from the mean perceived pressure in the upper body and ∼20% in the lower body. Participants rated pressures above their AOP for the upper body and below for the lower body. At the group level, there were differences in participants’ ratings for their relative AOP (7 out of 10) between day 1 and days 2 and 3 for the lower body, but no differences between sexes for the upper or lower body. Conclusions: The use of the perceived tightness scale does not provide reliable estimates of relative pressures over multiple visits. This method resulted in a wide range of relative AOPs within the same individual across days. This may preclude the use of this scale to set the pressure for those implementing practical blood flow restriction in the laboratory, gym, or clinic

Limb Occlusion Pressure: A Method to Assess Changes in Systolic Blood Pressure

Although often used as a surrogate, comparisons between traditional blood pressure measurements and limb occlusion assessed via hand-held Doppler have yet to be completed. Using limb occlusion pressure as a method of assessing systolic pressure is of interest to those studying the acute effects of blood flow restriction, where the removal of the cuff may alter the physiological response. Purpose: We sought to determine how changes in limb occlusion pressure track with changes in traditional assessments of blood pressure. Basic Procedures: Limb occlusion pressure measured by hand-held Doppler and blood pressure measured by an automatic blood pressure cuff were assessed at rest and following isometric knee extension (post and 5 minutes post). Main Findings: Each individual had a similar dispersion from the mean value for both the limb occlusion pressure measurement and traditional systolic blood pressure measurement [BF10: 0.33; median (95% credible interval): 0.02 (−6.0, 5.9) %]. In response to lower body isometric exercise, blood pressure changed across time. The difference between measurements was small at immediately post and 5 minutes post. The Bayes factors were in the direction of the null but did not exceed the threshold needed to accept the null hypothesis. However, at 5 minutes post, the differences were within the range of practical equivalence (within ± 4.6%). Principal Conclusions: Our findings suggest that changes in limb occlusion pressure measured by hand-held Doppler track similarly to traditional measurements of brachial systolic blood pressure following isometric knee extension exercise

The Basics of Training for Muscle Size and Strength: A Brief Review on the Theory

The periodization of resistance exercise is often touted as the most effective strategy for optimizing muscle size and strength adaptations. This narrative persists despite a lack of experimental evidence to demonstrate its superiority. In addition, the general adaptation syndrome, which provides the theoretical framework underlying periodization, does not appear to provide a strong physiological rationale that periodization is necessary. Hans Selye conducted a series of rodent studies which used toxic stressors to facilitate the development of the general adaptation syndrome. To our knowledge, normal exercise in humans has never been shown to produce a general adaptation syndrome. We question whether there is any physiological rationale that a periodized training approach would facilitate greater adaptations compared with nonperiodized approaches employing progressive overload. The purpose of this article is to briefly review currently debated topics within strength and conditioning and provide some practical insight regarding the implications these reevaluations of the literature may have for resistance exercise and periodization. In addition, we provide some suggestions for the continued advancement within the field of strength and conditioning

Injuries and Strength Training Practices in Collegiate Tennis

Strength and conditioning practices may influence injury rates in the sport of tennis. Methods: Coaches reported the number injuries over the past year. Coaches were also surveyed on whether their training program included training related to upper-body or lower-body strength, power, muscle growth, and eccentric exercise. Separate regression analyses were run in the upper and lower body to examine the relationship between injuries and participation in training focused on strength, power, growth, and maximal eccentric exercise. A total of 111 coaches were surveyed. The most frequent injuries observed were ankle sprains (144 injures), followed by paraspinal muscle strains (126 injuries). When pooled, there were a total of 355 lower-body and 260 upper-body injuries. Strength and conditioning practices explained 9.9% of the variance of injury rates in the upper body (R2 = 0.099). The only significant predictor of upper-body injury was participation in upper-body muscle growth training (β = 1.613, p = 0.013). In addition, training practices explained 11.1% of the variance of injury in the lower body (R2 = 0.111). Coaches value injury prevention exercise, sports-specific training and flexibility and mobility training the most, with muscle growth and maximal power ranked lowest. Additionally, the most frequent injuries observed in collegiate tennis players were ankle sprains (144 injures), followed by paraspinal muscle strains (126 injuries)

INTERPRETIVE AND STATISTICAL CONSIDERATIONS FOR RATIOS OF MUSCLE STRENGTH PER UNIT OF MUSCLE SIZE

BACKGROUND: Ratios of muscle strength per unit of muscle size are widely used. Statisticians point out that ratios often lead to spurious findings because they can 1) violate statistical assumptions, and 2) differ systematically across the range of denominator values simply due to mathematical artifact, not physiology. PURPOSE: Evaluate uneven scaling in muscle strength/size ratios via recommended isometry tests. METHODS: To evaluate working with ratios at the population level, 1999-2002 NHANES data including isokinetic knee extensor force and leg lean mass measures (n=2,848) were analyzed. To evaluate decision-making with sample data, we analyzed one-repetition maximum bicep curl (1RM) and bicep ultrasound muscle thickness data (n=151) from one of our previous studies. For each data set, regression lines were fit to numerator (strength) against denominator (size) variables via standardized major axis regression, testing for a non-zero y-intercept (indicates isometry issues). The ratio was then regressed on the denominator, with a non-zero slope indicating uneven scaling due to artifact. Recommended solutions including log transformation and intercept adjustment were also explored. RESULTS: For NHANES data, peak force (kg) regressed on leg lean mass (kg) yielded a line of y=-13.85+6.51x. The zero-intercept test indicated a non-isometric relationship, p\u3c0.001. When the strength/size ratio was regressed on leg lean mass, a systematic difference in the ratio (i.e., significant slope test) was observed across the leg lean mass values, y=5.13-0.06x, R2=0.008, p\u3c0.001. For the smaller sample, 1RM (kg) regressed on muscle thickness (cm) yielded a line of y=-8.28+8.14x. The zero-intercept test indicated a non-isometric relationship, p\u3c0.001. When the strength/size ratio was regressed on muscle thickness, a systematic difference in the ratio was observed across the muscle thickness values, y=3.30+0.58x,R2=0.118,p\u3c0.001. Log transformation did not alleviate scaling issues in either data set, although intercept adjustment may. CONCLUSION: Scaling issues were present in both cases, each in opposite direction. In one case, higher leg lean mass is associated with lower ratio scores, and in the other, greater muscle thickness is associated with greater ratio scores, each likely due to artifact. Ratio data should be evaluated case-by-case before subjected to analysis. Other techniques, i.e., ANCOVA or multiple regression, may better control for muscle size