The influence of training status on the drop in muscle strength after acute exercise

Single-leg disuse decreases skeletal muscle strength, size, and power in uninjured adults: A systematic review and meta-analysis

We aimed to quantify declines from baseline in lower limb skeletal muscle size and strength of uninjured adults following single-leg disuse. We searched EMBASE, Medline, CINAHL, and CCRCT up to 30 January 2022. Studies were included in the systematic review if they (1) recruited uninjured participants; (2) were an original experimental study; (3) employed a single-leg disuse model; and (4) reported muscle strength, size, or power data following a period of single-leg disuse for at least one group without a countermeasure. Studies were excluded if they (1) did not meet all inclusion criteria; (2) were not in English; (3) reported previously published muscle strength, size, or power data; or (4) could not be sourced from two different libraries, repeated online searches, and the authors. We used the Cochrane Risk of Bias Assessment Tool to assess risk of bias. We then performed random-effects meta-analyses on studies reporting measures of leg extension strength and extensor size. Our search revealed 6548 studies, and 86 were included in our systematic review. Data from 35 and 20 studies were then included in the meta-analyses for measures of leg extensor strength and size, respectively (40 different studies). No meta-analysis for muscle power was performed due to insufficient homogenous data. Effect sizes (Hedges' g_av ) with 95% confidence intervals for leg extensor strength were all durations = -0.80 [-0.92, -0.68] (n = 429 participants; n = 68 aged 40 years or older; n ≥ 78 females); ≤7 days of disuse = -0.57 [-0.75, -0.40] (n = 151); >7 days and ≤14 days = -0.93 [-1.12, -0.74] (n = 206); and >14 days = -0.95 [-1.20, -0.70] (n = 72). Effect sizes for measures of leg extensor size were all durations = -0.41 [-0.51, -0.31] (n = 233; n = 32 aged 40 years or older; n ≥ 42 females); ≤7 days = -0.26 [-0.36, -0.16] (n = 84); >7 days and ≤14 days = -0.49 [-0.67, -0.30] (n = 102); and >14 days = -0.52 [-0.74, -0.30] (n = 47). Decreases in leg extensor strength (cast: -0.94 [-1.30, -0.59] (n = 73); brace: -0.90 [-1.18, -0.63] (n = 106)) and size (cast: -0.61[-0.87, -0.35] (n = 41); brace: (-0.48 [-1.04, 0.07] (n = 41)) following 14 days of disuse did not differ for cast and brace disuse models. Single-leg disuse in adults resulted in a decline in leg extensor strength and size that reached a nadir beyond 14 days. Bracing and casting led to similar declines in leg extensor strength and size following 14 days of disuse. Studies including females and males and adults over 40 years of age are lacking.

Changes in strength, endurance, and fatigue during a resistance-training program for the triceps brachii muscle

CONTEXT

As a result of the adaptation process, some functional properties show different functions over time during strength training. Muscle strength and fatigue may show different adaptation patterns in reaching the improvement plateau after several weeks of training.

OBJECTIVE

To follow muscle endurance and fatigue values during resistance training of the elbow extensors in young nonathletes.

DESIGN

Descriptive laboratory study.

SETTING

Controlled laboratory.

PATIENTS OR OTHER PARTICIPANTS

Nineteen healthy young nonathletes (age = 21.0 ± 1.1 years; body mass index = 25.2 ± 2.9 kg/m(2)).

INTERVENTION(S)

Triceps brachii resistance training was performed on the isoacceleration dynamometer for 10 weeks (frequency = 5 times a week, 5 sets of 10 maximal elbow extensions, 1-minute resting period between sets).

MAIN OUTCOME MEASURE(S)

Measurements of endurance strength and fatigability were conducted using the same equipment, and endurance strength (ES), fatigue rate (FR), and decrease in strength (DS) were defined.

RESULTS

All measured values for triceps brachii strength changed after training (ES increased by 57%, FR decreased by 68%, and DS improved by 59%; P < .001). No correlation was found between ES and the fatigability values-FR and DS (r(2) = 0.37 for FR and r(2) = 0.04 for DS; P > .05). The FR and DS trends showed specific functions, which reached a plateau after 4 weeks of training, and we found no further weekly changes in these values as the training continued. As an adaptation to exercise, ES showed a continuous, yet not linear, increase.

CONCLUSIONS

Fatigability in the triceps brachii decreased in the first 4 weeks of training. After that period, muscle functional properties improved as a result of increased endurance.

The microvascular volume of the Achilles tendon is increased in patients with tendinopathy at rest and after a 1-hour treadmill run

BACKGROUND

Achilles tendinopathy (AT) is initiated asymptomatically and is therefore often discovered at a very late stage.

PURPOSE

To elucidate whether the microvascular volume (MV) of the Achilles tendon is elevated in patients with AT compared with healthy controls during pre-exercise rest, after acute exercise, and 24 hours after exercise. Additionally, this study investigated the muscle activation pattern of the gastrocnemius muscle and the relative elasticity of the Achilles tendon during a 1-hour treadmill run in healthy patients and in patients with AT.

STUDY DESIGN

Controlled laboratory study.

METHODS

Real-time harmonic contrast-enhanced ultrasound (CEU) measurements of the MV of the Achilles tendon were taken in 18 volunteers (9 patients with AT, 9 healthy controls). The CEU analyses were conducted before exercise, immediately after a 1-hour treadmill run, and 24 hours after exercise. Surface electromyography (EMG) signals of the gastrocnemius were recorded continuously during the 1-hour treadmill run.

RESULTS

In both the controls and the patients with AT, the MV of the Achilles tendon was increased after exercise as compared with before exercise (P < .005). Additionally, the MV signal was significantly larger in the patients with AT before, immediately after, and 24 hours after the running exercise compared with values in healthy controls (P < .0001). The muscle activation pattern differed in patients with AT compared with controls in that controls had increased EMG amplitudes at the end of the 1-hour treadmill run in the medial and lateral gastrocnemius (P < .0001). Moreover, patients with AT had approximately 15% less elastic Achilles tendons at the beginning of the 1-hour treadmill run, a condition that did not change because of exercise.

CONCLUSION

Acute exercise increases the MV of the Achilles tendon in healthy patients and patients with AT in a similar manner. However, patients with AT have a significantly larger MV at all time points compared with healthy patients, supporting the hypothesis that microvascular changes may be involved in the pathogenesis of tendinopathy.

CLINICAL RELEVANCE

This study underlines that tendon flexibility is altered in patients with AT and that CEU is a promising tool to establish the early diagnosis of this condition.

The effect of acute exercise on collagen turnover in human tendons: influence of prior immobilization period

Mechanical loading of human tendon stimulates collagen synthesis, but the relationship between acute loading responses and training status of the tendon is not clear. We tested the effect of prolonged load deprivation on the acute loading-induced collagen turnover in human tendons, by applying the same absolute load to a relative untrained Achilles tendon (2-week immobilization period prior to acute loading) and a habitually loaded contra-lateral Achilles tendon, respectively, within the same individuals. Eight untrained, healthy males had one lower limb totally immobilized for 2 weeks, whereas the contra-lateral leg was used habitually. Following the procedure both Achilles tendons and calf muscles were loaded with the same absolute load during a 1-h treadmill run. Tissue collagen turnover was measured by microdialysis performed post-immobilization but pre-exercise around both Achilles tendons and compared to values obtained by 72-h post-exercise. Power Doppler was used to monitor alterations in intratendinous blood flow velocity of the Achilles tendon and MRI used to quantitate changes in tendon cross-section area. Acute loading resulted in an increased collagen synthesis 72 h after the run in both Achilles tendons (p < 0.05) with no significant difference. No signs of acute tendon overloading were demonstrated by Power Doppler, and tendon cross-section area did not change as a result of immobilization and reloading. The present study indicates that 2 weeks of tendon load deprivation is not sufficient to affect the normal adaptive response to loading determined as increased collagen synthesis of peritendinous Achilles tendon tissue in humans.

Effects of 2 weeks lower limb immobilization and two separate rehabilitation regimens on gastrocnemius muscle protein turnover signaling and normalization genes

BACKGROUND

Limb immobilization causes a rapid loss of muscle mass and strength that requires appropriate rehabilitation to ensure restoration of normal function. Whereas the knowledge of muscle mass signaling with immobilization has increased in recent years, the molecular regulation in the rehabilitation of immobilization-induced muscle atrophy is only sparsely studied. To investigate the phosphorylation and expression of candidate key molecular muscle mass regulators after immobilization and subsequent rehabilitation we performed two separate studies.

METHODS

We immobilized the lower limb for 2 weeks followed by the in-house hospital standard physiotherapy rehabilitation (Study 1). Secondly, we conducted an intervention study using the same 2 weeks immobilization protocol during which protein/carbohydrate supplementation was given. This was followed by 6 weeks of rehabilitation in the form of resistance training and continued protein/carbohydrate supplementation (Study 2). We obtained muscle biopsies from the medial gastrocnemius prior to immobilization (PRE), post-immobilization (IMMO) and post-rehabilitation (REHAB) and measured protein expression and phosphorylation of Akt, mTOR, S6k, 4E-BP1, GSK3β, ubiquitin and MURF1 and mRNA expression of Atrogin-1, MURF1, FOXO1, 3 and 4 as well as appropriate housekeeping genes.

RESULTS

In both studies, no changes in protein expression or phosphorylation for any measured protein were observed. In Study 1, FOXO3 and FOXO4 mRNA expression decreased after IMMO and REHAB compared to PRE, whereas other mRNAs remained unchanged. Interestingly, we found significant changes in expression of the putative housekeeping genes GAPDH, HADHA and S26 with immobilization in both studies.

CONCLUSIONS

In neither study, the changes in muscle mass associated with immobilization and rehabilitation were accompanied by expected changes in expression of atrophy-related genes or phosphorylation along the Akt axis. Unexpectedly, we observed significant changes in several of the so-called housekeeping genes GAPDH, HADHA and S26 with immobilization in both studies, thereby questioning the usefulness of these genes for normalization of RNA data purposes in muscle immobilization studies.