Can isometric testing substitute for the one repetition maximum squat test?

When measuring maximum strength, a high accuracy and precision is required to monitor the training adaptations. Based on available reliability parameters, the literature suggests the replacement of the one repetition maximum (1RM) by isometric testing to save testing time. However, from a statistical point of view, correlation coefficients do not provide the required information when aiming to replace one test by another. Therefore, the literature suggests the inclusion of the mean absolute error (MAE), the mean absolute percentage error (MAPE) for agreement analysis. Consequently, to check the replaceability of 1RM testing methods, the current study examined the agreement of isometric and dynamic testing methods in the squat and the isometric mid-thigh pull. While in accordance with the literature, correlations were classified high r = 0.638-0.828 and ICC = 0.630-0.828, the agreement analysis provided MAEs of 175.75-444.17 N and MAPEs of 16.16-57.71% indicating an intolerable high measurement error between isometric and dynamic testing conditions in the squat and isometric mid-thigh pull. In contrast to previous studies, using MAE, MAPE supplemented by CCC and BA analysis highlights the poor agreement between the included strength tests. The recommendation to replace 1RM testing with isometric testing routines in the squat does not provide suitable concordance and is not recommended.

Comparison of the effects of long-lasting static stretching and hypertrophy training on maximal strength, muscle thickness and flexibility in the plantar flexors.

Maximal strength measured via maximal voluntary contraction is known as a key factor in competitive sports performance as well as injury risk reduction and rehabilitation. Maximal strength and hypertrophy are commonly trained by performing resistance training programs. However, literature shows that long-term, long-lasting static stretching interventions can also produce significant improvements in maximal voluntary contraction. The aim of this study is to compare increases in maximal voluntary contraction, muscle thickness and flexibility after 6 weeks of stretch training and conventional hypertrophy training. Sixty-nine (69) active participants (f = 30, m = 39; age 27.4 ± 4.4 years, height 175.8 ± 2.1 cm, and weight 79.5 ± 5.9 kg) were divided into three groups: IG1 stretched the plantar flexors continuously for one hour per day, IG2 performed hypertrophy training for the plantar flexors (5 × 10-12 reps, three days per week), while CG did not undergo any intervention. Maximal voluntary contraction, muscle thickness, pennation angle and flexibility were the dependent variables. The results of a series of two-way ANOVAs show significant interaction effects (p < 0.05) for maximal voluntary contraction (ƞ2 = 0.143-0.32, p < 0.006), muscle thickness (ƞ2 = 0.11-0.14, p < 0.021), pennation angle (ƞ2 = 0.002-0.08, p = 0.077-0.625) and flexibility (ƞ2 = 0.089-0.21, p < 0.046) for both the stretch and hypertrophy training group without significant differences (p = 0.37-0.99, d = 0.03-0.4) between both intervention groups. Thus, it can be hypothesized that mechanical tension plays a crucial role in improving maximal voluntary contraction and muscle thickness irrespective whether long-lasting stretching or hypertrophy training is used. Results show that for the calf muscle, the use of long-lasting stretching interventions can be deemed an alternative to conventional resistance training if the aim is to increase maximal voluntary contraction, muscle thickness and flexibility. However, the practical application seems to be strongly limited as a weekly stretching duration of up to 7 h a week is opposed by 3 × 15 min of common resistance training.

Influence of Long-Lasting Static Stretching Intervention on Functional and Morphological Parameters in the Plantar Flexors: A Randomized Controlled Trial.

ABSTRACT: Warneke, K, Keiner, M, Wohlann, T, Lohmann, LH, Schmitt, T, Hillebrecht, M, Brinkmann, A, Hein, A, Wirth, K, and Schiemann, S. Influence of long-lasting static stretching intervention on functional and morphological parameters in the plantar flexors: a randomised controlled trial. J Strength Cond Res 37(10): 1993-2001, 2023-Animal studies show that long-lasting stretching training can lead to significant hypertrophy and increases in maximal strength. Accordingly, previous human studies found significant improvements in maximal voluntary contraction (MVC), flexibility, and muscle thickness (MTh) using constant angle long-lasting stretching. It was hypothesized that long-lasting stretching with high intensity will lead to sufficient mechanical tension to induce muscle hypertrophy and maximal strength gains. This study examined muscle cross-sectional area (MCSA) using magnetic resonance imaging (MRI). Therefore, 45 well-trained subjects (f: 17, m: 28, age: 27.7 ± 3.0 years, height: 180.8 ± 4.9 cm, mass: 80.4 ± 7.2 kg) were assigned to an intervention group (IG) that stretched the plantar flexors 6 × 10 minutes per day for 6 weeks or a control group (CG). Data analysis was performed using 2-way ANOVA. There was a significant Time × Group interaction in MVC ( p < 0.001-0.019, ƞ 2 = 0.158-0.223), flexibility ( p < 0.001, ƞ 2 = 0.338-0.446), MTh ( p = 0.002-0.013, ƞ 2 = 0.125-0.172), and MCSA ( p = 0.003-0.014, ƞ 2 = 0.143-0.197). Post hoc analysis showed significant increases in MVC ( d = 0.64-0.76), flexibility ( d = 0.85-1.12), MTh ( d = 0.53-0.6), and MCSA ( d = 0.16-0.3) in IG compared with CG, thus confirming previous results in well-trained subjects. Furthermore, this study improved the quality for the morphological examination by investigating both heads of the gastrocnemius with MRI and sonography. Because stretching can be used passively, an application in rehabilitation settings seems plausible, especially if no commonly used alternatives such as strength training are applicable.

Effects of a Home-Based Stretching Program on Bench Press Maximum Strength and Shoulder Flexibility.

Recent research showed significant stretch-mediated maximum strength increases when performing stretching between 5 to 120 minutes per day with the calf muscle. However, since the practical applicability of these long stretching durations was questioned and studies exploring the transferability to the upper body are scarce, the aim of this study was to investigate the possibility of using a home-based stretching program to induce significant increases in maximum strength and flexibility. Therefore, 31 recreationally active participants (intervention group: 18, control group: 13) stretched the pectoralis major for 15min/day for eight weeks, incorporating three different stretching exercises. The maximum strength was tested isometrically and dynamically in the bench press (one-repetition maximum: 1RM) as well as shoulder range of motion (ROM) performing bilateral shoulder rotation with a scaled bar. Using a two-way analysis of variance (ANOVA) with repeated measures, the results showed high magnitude Time effects (ƞ² = 0.388-0.582, p < 0.001) and Group*Time interaction (ƞ² = 0.281-0.53, p < 0.001-0.002), with increases of 7.4 ± 5.6% in 1RM and of 9.8 ± 5.0% in ROM test in the intervention group. In the isometric testing, there was a high-magnitude Time effect (ƞ² = 0.271, p = 0.003), however, the Group*Time interaction failed to reach significance (p = 0.75). The results are in line with previous results that showed stretch-mediated maximum strength increases in the lower extremity. Future research should address the underlying physiological mechanisms such as muscle hypertrophy, contraction conditions as well as pointing out the relevance of intensity, training frequency and stretching duration.

Stressing the Relevance of Differentiating between Systematic and Random Measurement Errors in Ultrasound Muscle Thickness Diagnostics.

BACKGROUND: The majority of studies that explore changes in musculature following resistance training interventions or examine atrophy due to immobilization or sarcopenia use ultrasound imaging. While most studies assume acceptable to excellent reliability, there seems to be unawareness of the existing absolute measurement errors. As early as 1998, methodological research addressed a collective unawareness of the random measurement error and its practical indications. Referring to available methodological approaches, within this work, we point out the limited value of focusing on relative, correlation-based reliability indices for the interpretability in scientific research but also for clinical application by assessing 1,512 muscle thickness values from more than 400 ultrasound images. To account for intra- and inter-day repeatability, data were collected on two consecutive days within four testing sessions. Commonly-stated reliability values (ICC, CV, SEM and MDC) were calculated, while evidence-based agreement analyses were applied to provide the accompanied systematic and random measurement error. RESULTS: While ICCs in the range of 0.832 to 0.998 are in accordance with the available literature, the mean absolute percentage error ranges from 1.34 to 20.38% and the mean systematic bias from 0.78 to 4.01 mm (all p ≤ 0.013), depending on the measurement time points chosen for data processing. CONCLUSIONS: In accordance with prior literature, a more cautious interpretation of relative reliability values should be based on included systematic and random absolute measurement scattering. Lastly, this paper discusses the rationale for including different measurement error statistics when determining the validity of pre-post changes, thus, accounting for the certainty of evidence.

Discussing Conflicting Explanatory Approaches in Flexibility Training Under Consideration of Physiology: A Narrative Review.

The mechanisms underlying range of motion enhancements via flexibility training discussed in the literature show high heterogeneity in research methodology and study findings. In addition, scientific conclusions are mostly based on functional observations while studies considering the underlying physiology are less common. However, understanding the underlying mechanisms that contribute to an improved range of motion through stretching is crucial for conducting comparable studies with sound designs, optimising training routines and accurately interpreting resulting outcomes. While there seems to be no evidence to attribute acute range of motion increases as well as changes in muscle and tendon stiffness and pain perception specifically to stretching or foam rolling, the role of general warm-up effects is discussed in this paper. Additionally, the role of mechanical tension applied to greater muscle lengths for range of motion improvement will be discussed. Thus, it is suggested that physical training stressors can be seen as external stimuli that control gene expression via the targeted stimulation of transcription factors, leading to structural adaptations due to enhanced protein synthesis. Hence, the possible role of serial sarcomerogenesis in altering pain perception, reducing muscle stiffness and passive torque, or changes in the optimal joint angle for force development is considered as well as alternative interventions with a potential impact on anabolic pathways. As there are limited possibilities to directly measure serial sarcomere number, longitudinal muscle hypertrophy remains without direct evidence. The available literature does not demonstrate the necessity of only using specific flexibility training routines such as stretching to enhance acute or chronic range of motion.

Resistance Training Causes the Stretch-Induced Force Deficit-A Randomized Cross-Over Study.

PURPOSE: Stretch-induced force deficit suggests an acute stretch-specific strength capacity loss, which is commonly attributed to EMG reductions. Since those deficits could also be attributed to general fatigue induced by overloading the muscle, this study aimed to compare stretching with an exhausting calf raise programme to compare strength and stretching responses. METHOD: This study included 16 participants with different, high-duration calf muscle stretching effects (10, 20, 30 min of stretching) with resistance training (RT) (3 × 12 repetitions) performed until muscle failure, by using a cross-over study design with pre-post comparisons. Strength was tested via isometric plantar flexor diagnostics, while flexibility was assessed using the knee-to-wall test (KtW) and an isolated goniometer test. RESULTS: Using a three-way ANOVA, RT strength decreases were greater compared to 10 and 20 min of stretching (p = 0.01-0.02), but similar to those of 30 min of stretching. ROM in the KtW showed no specific stretch-induced increases, while only the stretching conditions enhanced isolated tested ROM (p < 0.001-0.008). No RT-related isolated ROM increases were observed. CONCLUSIONS: The results showed both interventions had similar effects on strength and ROM in the calf muscles. More holistic explanatory approaches such as fatigue and warm-up are discussed in the manuscript and call for further research.

Effects of daily static stretch training over 6 weeks on maximal strength, muscle thickness, contraction properties, and flexibility.

Purpose: Static stretch training (SST) with long stretching durations seems to be sufficient to increase flexibility, maximum strength (MSt) and muscle thickness (MTh). However, changes in contraction properties and effects on muscle damage remain unclear. Consequently, the objective of the study was to investigate the effects of a 6-week self-performed SST on MSt, MTh, contractile properties, flexibility, and acute response of creatine kinase (CK) 3 days after SST. Methods: Forty-four participants were divided into a control (CG, n = 22) and an intervention group (IG, n = 22), who performed a daily SST for 5 min for the lower limb muscle group. While isometric MSt was measured in leg press, MTh was examined via sonography and flexibility by functional tests. Muscle stiffness and contraction time were measured by tensiomyography on the rectus femoris. Additionally, capillary blood samples were taken in the pretest and in the first 3 days after starting SST to measure CK. Results: A significant increase was found for MSt (p < 0.001, η 2 = 0.195) and flexibility in all functional tests (p < 0.001, η 2 > 0.310). Scheffé post hoc test did not show significant differences between the rectus femoris muscle inter- and intragroup comparisons for MTh nor for muscle stiffness and contraction time (p > 0.05, η 2 < 0.100). Moreover, CK was not significantly different between IG and CG with p > 0.05, η 2 = 0.032. Discussion: In conclusion, the increase in MSt cannot be exclusively explained by muscular hypertrophy or the increased CK-related repair mechanism after acute stretching. Rather, neuronal adaptations have to be considered. Furthermore, daily 5-min SST over 6 weeks does not seem sufficient to change muscle stiffness or contraction time. Increases in flexibility tests could be attributed to a stretch-induced change in the muscle-tendon complex.

Maximal strength measurement: A critical evaluation of common methods-a narrative review.

Measuring maximal strength (MSt) is a very common performance diagnoses, especially in elite and competitive sports. The most popular procedure in test batteries is to test the one repetition maximum (1RM). Since testing maximum dynamic strength is very time consuming, it often suggested to use isometric testing conditions instead. This suggestion is based on the assumption that the high Pearson correlation coefficients of r ≥ 0.7 between isometric and dynamic conditions indicate that both tests would provide similar measures of MSt. However, calculating r provides information about the relationship between two parameters, but does not provide any statement about the agreement or concordance of two testing procedures. Hence, to assess replaceability, the concordance correlation coefficient (ρ c) and the Bland-Altman analysis including the mean absolute error (MAE) and the mean absolute percentage error (MAPE) seem to be more appropriate. Therefore, an exemplary model based on r = 0.55 showed ρ c = 0.53, A MAE of 413.58 N and a MAPE = 23.6% with a range of -1,000-800 N within 95% Confidence interval (95%CI), while r = 0.7 and 0.92 showed ρ c = 0.68 with a MAE = 304.51N/MAPE = 17.4% with a range of -750 N-600 N within a 95% CI and ρ c = 0.9 with a MAE = 139.99/MAPE = 7.1% with a range of -200-450 N within a 95% CI, respectively. This model illustrates the limited validity of correlation coefficients to evaluate the replaceability of two testing procedures. Interpretation and classification of ρ c, MAE and MAPE seem to depend on expected changes of the measured parameter. A MAPE of about 17% between two testing procedures can be assumed to be intolerably high.

Influence of One Hour versus Two Hours of Daily Static Stretching for Six Weeks Using a Calf-Muscle-Stretching Orthosis on Maximal Strength.

Rebuilding strength capacity is of crucial importance in rehabilitation since significant atrophy due to immobilization after injury and/or surgery can be assumed. To increase maximal strength (MSt), strength training is commonly used. The literature regarding animal studies show that long-lasting static stretching (LStr) interventions can also produce significant improvements in MSt with a dose-response relationship, with stretching times ranging from 30 min to 24 h per day; however, there is limited evidence in human studies. Consequently, the aim of this study is to investigate the dose-response relationship of long-lasting static stretching on MSt. A total of 70 active participants (f = 30, m = 39; age: 27.4 ± 4.4 years; height: 175.8 ± 2.1 cm; and weight: 79.5 ± 5.9 kg) were divided into three groups: IG1 and IG2 both performed unilateral stretching continuously for one (IG1) or two hours (IG2), respectively, per day for six weeks, while the CG served as the non-intervened control. MSt was determined in the plantar flexors in the intervened as well as in the non-intervened control leg to investigate the contralateral force transfer. Two-way ANOVA showed significant interaction effects for MSt in the intervened leg (ƞ2 = 0.325, p < 0.001) and in the contralateral control leg (ƞ2 = 0.123, p = 0.009), dependent upon stretching time. From this, it can be hypothesized that stretching duration had an influence on MSt increases, but both durations were sufficient to induce significant enhancements in MSt. Thus, possible applications in rehabilitation can be assumed, e.g., if no strength training can be performed, atrophy could instead be reduced by performing long-lasting static stretch training.

Influence of Long-Lasting Static Stretching on Maximal Strength, Muscle Thickness and Flexibility.

Background: In animal studies long-term stretching interventions up to several hours per day have shown large increases in muscle mass as well as maximal strength. The aim of this study was to investigate the effects of a long-term stretching on maximal strength, muscle cross sectional area (MCSA) and range of motion (ROM) in humans. Methods: 52 subjects were divided into an Intervention group (IG, n = 27) and a control group (CG, n = 25). IG stretched the plantar flexors for one hour per day for six weeks using an orthosis. Stretching was performed on one leg only to investigate the contralateral force transfer. Maximal isometric strength (MIS) and 1RM were both measured in extended knee joint. Furthermore, we investigated the MCSA of IG in the lateral head of the gastrocnemius (LG) using sonography. Additionally, ROM in the upper ankle was investigated via the functional "knee to wall stretch" test (KtW) and a goniometer device on the orthosis. A two-way ANOVA was performed in data analysis, using the Scheffé Test as post-hoc test. Results: There were high time-effects (p = 0.003, ƞ² = 0.090) and high interaction-effect (p < 0.001, ƞ²=0.387) for MIS and also high time-effects (p < 0.001, ƞ²=0.193) and interaction-effects (p < 0.001, ƞ²=0,362) for 1RM testing. Furthermore, we measured a significant increase of 15.2% in MCSA of LG with high time-effect (p < 0.001, ƞ²=0.545) and high interaction-effect (p=0.015, ƞ²=0.406). In ROM we found in both tests significant increases up to 27.3% with moderate time-effect (p < 0.001, ƞ²=0.129) and high interaction-effect (p < 0.001, ƞ²=0.199). Additionally, we measured significant contralateral force transfers in maximal strength tests of 11.4% (p < 0.001) in 1RM test and 1.4% (p=0.462) in MIS test. Overall, there we no significant effects in control situations for any parameter (CG and non-intervened leg of IG). Discussion: We hypothesize stretching-induced muscle damage comparable to effects of mechanical load of strength training, that led to hypertrophy and thus to an increase in maximal strength. Increases in ROM could be attributed to longitudinal hypertrophy effects, e.g., increase in serial sarcomeres. Measured cross-education effects could be explained by central neural adaptations due to stimulation of the stretched muscles.

Using Daily Stretching to Counteract Performance Decreases as a Result of Reduced Physical Activity-A Controlled Trial.

There are many reasons for reduced physical activity leading to reduced maximal strength and sport-specific performance, such as jumping performance. These include pandemic lockdowns, serious injury, or prolonged sitting in daily work life. Consequently, such circumstances can contribute to increased morbidity and reduced physical performance. Therefore, a demand for space-saving and home-based training routines to counteract decreases in physical performance is suggested in the literature. This study aimed to investigate the possibility of using daily static stretching using a stretching board to counteract inactivity-related decreases in performance. Thirty-five (35) participants were either allocated to an intervention group (IG), performing a daily ten-minute stretch training combined with reduced physical activity or a reduced physical activity-only group (rPA). The effects on maximal voluntary contraction, range of motion using the knee-to-wall test, countermovement jump height (CMJheight), squat jump height (SJheight), drop jump height (DJheight), contact time (DJct) and the reactive strength index (DJRSI) were evaluated using a pre-test-post-test design. The rPA group reported reduced physical activity because of lockdown. Results showed significant decreases in flexibility and jump performance (d = -0.11--0.36, p = 0.004-0.046) within the six weeks intervention period with the rPA group. In contrast, the IG showed significant increases in MVC90 (d = 0.3, p < 0.001) and ROM (d = 0.44, p < 0.001) with significant improvements in SJheight (d = 0.14, p = 0.002), while no change was measured for CMJheight and DJ performance. Hence, 10 min of daily stretching seems to be sufficient to counteract inactivity-related performance decreases in young and healthy participants.

Repetitive Peripheral Magnetic Nerve Stimulation (rPMS) as Adjuvant Therapy Reduces Skeletal Muscle Reflex Activity.

Background: The reduction of muscle hypertonia and spasticity, as well as an increase in mobility, is an essential prerequisite for the amelioration of physiotherapeutical treatments. Repetitive peripheral magnetic nerve stimulation (rPMS) is a putative adjuvant therapy that improves the mobility of patients, but the underlying mechanism is not entirely clear. Methods: Thirty-eight participants underwent either an rPMS treatment (N = 19) with a 5 Hz stimulation protocol in the posterior tibial nerve or sham stimulation (N = 19). The stimulation took place over 5 min. The study was conducted in a pre-test post-test design with matched groups. Outcome measures were taken at the baseline and after following intervention. Results: The primary outcome was a significant reduction of the reflex activity of the soleus muscle, triggered by a computer-aided tendon-reflex impact. The pre-post differences of the tendon reflex response activity were -23.7% (P < 0.001) for the treatment group. No significant effects showed in the sham stimulation group. Conclusion: Low-frequency magnetic stimulation (5 Hz rPMS) shows a substantial reduction of the tendon reflex amplitude. It seems to be an effective procedure to reduce muscular stiffness, increase mobility, and thus, makes the therapeutic effect of neuro-rehabilitation more effective. For this reason, the 5 Hz rPMS treatment might have the potential to be used as an adjuvant therapy in the rehabilitation of gait and posture control in patients suffering from limited mobility due to spasticity. The effect observed in this study should be investigated conjoined with the presented method in patients with impaired mobility due to spasticity.