Peter J. Abernethy

Concurrent strength and endurance training: A review

AbstractConcurrent strength and endurance training appears to inhibit strength development when compared with strength training alone. Our understanding of the nature of this inhibition and the mechanisms responsible for it is limited at present. This is due to the difficulties associated with comparing results of studies which differ markedly in a number of design factors, including the mode, frequency, duration and intensity of training, training history of participants, scheduling of training sessions and dependent variable selection. Despite these difficulties, both chronic and acute hypotheses have been proposed to explain the phenomenon of strength inhibition during concurrent training. The chronic hypothesis contends that skeletal muscle cannot adapt metabolically or morphologically to both strength and endurance training simultaneously. This is because many adaptations at the muscle level observed in response to strength training are different from those observed after endurance training. The observation that changes in muscle fibre type and size after concurrent training are different from those observed after strength training provide some support for the chronic hypothesis. The acute hypothesis contends that residual fatigue from the endurance component of concurrent training compromises the ability to develop tension during the strength element of concurrent training. It is proposed that repeated acute reductions in the quality of strength training sessions then lead to a reduction in strength development over time. Peripheral fatigue factors such as muscle damage and glycogen depletion have been implicated as possible fatigue mechanisms associated with the acute hypothesis. Further systematic research is necessary to quantify the inhibitory effects of concurrent training on strength development and to identify different training approaches that may overcome any negative effects of concurrent training.

Strength and Power Assessment: Issues, Controversies and Challenges

SummaryAthletic strength and power refer to the forces or torques generated during sporting activity. Their assessment can be used for strength diagnosis or talent identification, to monitor the effects of training interventions and to estimate the relative significance of strength and power to particular athletic pursuits. However, strength and power assessment is a difficult task. Reasons for this include: the fledgling status of research within the area, our limited understanding of the mechanisms underpinning strength and power performance and development, and limitations associated with various forms of dynamometry. This article describes a frame work for the collection of data which may ultimately lead to recommendations for the assessment of strength and power in sporting contexts. Such a framework will be evolutionary and depends upon synergistic improvements in our understanding of: the physiological mechanisms underpinning strength and power development; the effect that various training regimens have upon the development of strength and power; and factors influencing the validity and reliability of dynamometry.Currently, isometric, isoinertial and isokinetic dynamometry are employed in assessment. Each form has its supporters and detractors. Basically, proponents and critics of isokinetic and isometric dynamometry emphasise their apparently high external and apparently low internal validity respectively. While the converse applies for isoinertial dynamometry. It appears that all 3 modalities can have acceptable reliability, however this should be established rather than assumed, as the reliability of each can be threatened by a number of considerations (e.g. instruction for isometric tasks, the impact of weight used during weighted jumping tasks, and the effects of gravity and feedback on isokinetic performance). While reliability is a seminal issue in assessment, it is not the only critical issue. Specifically, there has been little research into the correlation between strength and power measures and athletic performance. This work is central to the use of such indices in talent identification. To date, this work has generally been limited to heterogeneous rather than homogeneous groups. More work is required in this area. Furthermore, not all modes of assessment are sensitive or similarly sensitive to various training interventions. This suggests that these modalities are measuring different neuromuscular qualities. How these qualities relate to performance requires more work, and will determine the contexts in which various strength and power assessment modalities and protocols are used. Following are conclusions from the review: (i) it is unlikely that one assessment procedure can be used for a multitude of ends (e.g. talent identification and monitoring the effects of training); (ii) different levels of athlete ability within a given sport may require different assessment regimens; (iii) minor changes in procedure may alter the usefulness of a procedure and (iv) we must be prepared to question assumptions pervading the field which are based upon anecdotal evidence. There are limitations with, and should be delimitations in the use of the various protocols and forms of dynamometry.

Acute and chronic response of skeletal muscle to resistance exercise.

SummarySkeletal muscle tissue is sensitive to the acute and chronic stresses associated with resistance training. These responses are influenced by the structure of resistance activity (i.e. frequency, load and recovery) as well as the training history of the individuals involved. There are histochemical and biochemical data which suggest that resistance training alters the expression of myosin heavy chains (MHCs). Specifically, chronic exposure to bodybuilding and power lifting type activity produces shifts towards the MHC I and IIb isoforms, respectively. However, it is not yet clear which training parameters trigger these differential expressions of MHC isoforms. Interestingly, many programmes undertaken by athletes appear to cause a shift towards the MHC I isoform. Increments in the cross-sectional area of muscle after resistance training can be primarily attributed to fibre hypertrophy. However, there may be an upper limit to this hypertrophy. Furthermore, significant fibre hypertrophy appears to follow the sequence of fast twitch fibre hypertrophy preceding slow twitch fibre hypertrophy. Whilst some indirect measures of fibre number in living humans suggest that there is no interindividual variation, postmortem evidence suggests that there is. There are also animal data arising from investigations using resistance training protocols which suggest that chronic exercise can increase fibre number. Furthermore, satellite cell activity has been linked to myotube formation in the human.However, other animal models (i.e. compensatory hypertrophy) do not support the notion of fibre hyperplasia. Even if hyperplasia does occur, its effect on the cross-sectional area of muscle appears to be small. Phosphagen and glycogen metabolism, whilst important during resistance activity appear not to normally limit the performance of resistance activity. Phosphagen and related enzyme adaptations are affected by the type, structure and duration of resistance training. Whilst endogenous glycogen reserves may be increased with prolonged training, typical isotonic training for less than 6 months does not seem to increase glycolytic enzyme activity. Lipid metabolism may be of some significance in bodybuilding type activity. Thus, not surprisingly, oxidative enzyme adaptations appear to be affected by the structure and perhaps the modality of resistance training. The dilution of mitochondrial volume and endogenous lipid densities appears mainly because of fibre hypertrophy.

Acute effects of high-intensity endurance exercise on subsequent resistance activity

This study investigated the effect of high-intensity endurance on subsequent isoinertial and isokinetic resistance exercise. One woman and five men (mean 6 SD: age 5 20.3 6 2.5 years; body mass 5 75.1 6 10.2 kg; height 5 177.8 6 10.3 cm) performed isoinertial and isokinetic resistance exercise under control conditions (no experimental intervention) and after an acute bout of high-intensity endurance exercise. Endurance exercise consisted of five 5-minute bouts of incremental cycle exercise at between 40 and 100% of peak cycle ergometer oxygen consumption (peak V˙ O2). Isoinertial resistance exercise consisted of three sets of squats with a load of 80% of one repetition maximum. Isokinetic resistance exercise consisted of five repetitions of leg extensions performed at five different contractile speeds (1.05, 2.09, 3.14, 4.19, and 5.24 rad•s21). Significant reductions in isokinetic torque at 0.52 rad from full extension (T30) were observed after high-intensity endurance exercise. Endurance exercise also caused significant reductions in the number of isoinertial squat lifts performed. Plasma lactate values, measured before subjects performed resistance activity, were significantly higher after high intensity endurance exercise (6.16 6 2.28 mmol•L21) when compared with the control condition (0.50 6 0.45 mmol•L21). It was concluded that an acute bout of high-intensity endurance exercise may inhibit performance in a subsequent bout of resistance activity.

Concurrent Strength and Endurance Training: The Influence of Dependent Variable Selection

Twenty-six active university students were randomly allocated to resistance (R, n 5 9), endurance (E, n 5 8), and concurrent resistance and endurance (C, n 5 9) training con-ditions. Training was completed 3 times per week in all conditions, with endurance training preceding resistance training in the C group. Resistance training involved 4 sets of upper- and lower-body exercises with loads of 4–8 repetition maximum (RM). Each endurance training session consisted of five 5-minute bouts of incremental cycle exercise at between 40 and 100% of peak oxygen uptake (VO2peak). Parameters measured prior to and following training included strength (1RM and isometric and isokinetic [1.04, 3.12, 5.20, and 8.67 rad·s 21] strength), VO2peak and Wingate test performance (peak power output [PPO], average power, and relative power decline). Significant improvements in 1RM strength were observed in the R and C groups following training. VO2peak significantly increased in E and C but was significantly reduced in R after training. Effect size (ES) transformations on the other dependent variables suggested that performance changes in the C group were not always similar to changes in the R or E groups. These ES data suggest that statistical power and dependent variable selection are significant issues in enhancing our insights into concurrent training. It may be necessary to assess a range of performance parameters to monitor the relative effectiveness of a particular concurrent training regimen.

Resistance training frequency: strength and myosin heavy chain responses to two and three bouts per week

Abstract Seventeen subjects performed resistance training of the leg extensor and flexor muscle groups two (2/wk) or three (3/wk) times per week. Changes in the relative myosin heavy chain (MHC) isoform contents (I, IIa and IIx) of the vastus lateralis and isometric, isokinetic and squat-lift one-repetition maximum (1RM) strength were compared between conditions after both a common training period (6 weeks) and number of training sessions (18). After 6 weeks and 18 sessions (9 weeks for the 2/wk group), increments in 1RM strength for the 3/wk and 2/wk groups were similar [effect size (ES) differences ≈0.3, 3/wk > 2/wk], whereas the 2/wk group presented greater isokinetic (ES differences = 0.3–1.2) and isometric (ES differences ≈0.7) strength increases than the 3/wk condition. A significant (P < 0.05) increase in MHC IIa percentage was evident for the 2/wk group after 18 sessions. Both training groups exhibited a trend towards a reduction in the relative MHC IIx and an increase in MHC IIa contents (ES range = 0.5–1.24). However, correlations between changes in the strength and MHC profiles were weak (r2: 0.0–0.5). Thus, isometric and isokinetic strength responses to variations in training frequency differed from 1RM strength responses, and changes in strength were not strongly related to alterations in relative MHC content.

Changes in the myosin heavy chain isoform profile of the triceps brachii muscle following 12 weeks of resistance training

The purpose of this investigation was to determine whether 12 weeks of resistance training, which increased arm girth (5%) and forearm extensor strength (39%), also altered the myosin heavy chain (MHC) characteristics of the triceps brachii muscle. Fifteen healthy, active men volunteered to participate under experimental (n = 11) or control (n = 4) conditions. The experimental group completed four sets of eight to 12 repetitions for each exercise (i.e. triceps pushdown, close grip bench press, triceps kickbacks and biceps curl) with loads of between 70–75% of one repetition maximum (1RM) three times a week. The inter-set and inter-exercise recovery period was only 90 s. Skeletal muscle tissue was removed from the triceps brachii muscle prior to (W0) and following 4 (W4), 8 (W8) and 12 (W12) weeks of the investigation. Samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). MHC isoform composition in the control group did not change significantly. However, the percentage of MHC type IIb isoform decreased significantly from W0 to W4 and again from W4 to W12 [W0: 39.7 (9.2); W12: 29.2 (8.2)%] in the experimental condition. The increments in MHC type IIa [W0: 34.0 (9.9); W12: 41.5 (10.4)] and type I [W0: 26.3 (7.9); W12: 29.3 (9.6)] isoforms were not significant for the experimental group. However, the effect size (ES) transformation of changes in types IIa MHC content was moderate (ES = 0.75). Changes in MHC isoform content were not significantly correlated with changes in 1RM strength for the triceps pushdown exercise. These data indicated that resistance training rapidly, and in an ongoing manner, changed the contractile protein profile of trained skeletal muscle. However, changes in MHC isoform composition in the first 12 weeks of training were not implicated in the development of 1RM triceps pushdown strength.

Acute adaptation to low volume eccentric exercise

PURPOSE Many symptoms of eccentric muscle damage can be substantially reduced if a similar eccentric bout is repeated within several weeks of the initial bout. The purpose of this study was to determine whether a nondamaging, low repetition, low volume eccentric exercise bout could also provide a protective/adaptive effect. METHODS Subjects were assigned to a control (CON), eccentric exercise (ECC), or low volume familiarized eccentric exercise group (LV+ECC). Before the study, the LV+ECC group performed six maximal eccentric contractions during two familiarization sessions. The main eccentric bout targeted the elbow flexor muscle group and consisted of 36 maximal eccentric contractions. Muscle soreness, upper arm girth, elbow angle, creatine kinase activity, isometric torque, and concentric and eccentric torque at 0.52 and 3.14 rad.s-1 were assessed 0, 1, 2, 3, 4, 7, and 10 d postexercise. RESULTS No evidence of muscle damage was observed as a result of the low volume eccentric bouts. Nevertheless, with the exception of muscle soreness and concentric torque, all variables recovered more rapidly in the LV+ECC group (P < 0.05). CONCLUSION Adaptation to eccentric exercise can occur in the absence of significant muscle damage. Exposure to a small number of nondamaging eccentric contractions can significantly improve recovery after a subsequent damaging eccentric bout. Furthermore, this adaptation appears to be mode-specific and not applicable to concentric contractions.

Changes in leg strength 8 and 32 h after endurance exercise

The aim of this study was to determine the effects of a single bout of endurance exercise on subsequent strength performance. Eight males with a long history of resistance training performed isokinetic, isometric and isotonic leg extension strength tests 8 and 32 h after 50 min of cycle ergometry at 70-110% of critical power. The participants also completed a control condition in which no cycling was performed. Plasma lactate and ammonia were measured before and immediately after each strength test. Isokinetic, isometric and isotonic leg extension torques were not significantly different 8 or 32 h after endurance exercise compared with the control condition ( P > 0.05). A large (50.3%), but not statistically significant, increase in plasma ammonia was evident during the strength tests performed 8 h after endurance exercise, while a significant ( P ≪ 0.05) increase in ammonia was also seen 32 h after endurance exercise. No significant changes in plasma ammonia were evident in the control condition. Our results suggest that leg extension strength was not compromised by an earlier bout of endurance cycling. However, metabolic activity during the strength tests might have been altered by the preceding bout of endurance exercise.

Effects of carbohydrate restriction on strength performance

This study investigated the effect of a carbohydrate restriction program on performance in a bout of isoinertial and isokinetic strength exercise. One female and five male subjects (mean +/- SD: age = 20.3 +/- 2.3 years; body mass = 74.6 +/- 11.5 kg; height 177.0 +/- 8.8 cm) performed isoinertial and isokinetic strength exercise under control conditions (no experimental intervention) and after a 2-day carbohydrate restriction program. The carbohydrate restriction program consisted of 60 minutes of cycling at 75% of peak cycle ergometer oxygen consumption (PVO2), followed by four 1-minute bouts at 100% of PVO2, followed by 2 days of reduced carbohydrate intake (1.2 +/- 0.5 g.kg(-1).d(-1)). Isoinertial strength exercise was three sets of squats with a load of 80% of one repetition maximum. Isokinetic strength exercise was five repetitions of leg extensions performed at five different contractile speeds (1.05, 2.09, 3.14, 4.19, and 5.24 rad.s(-1)). The carbohydrate restriction program caused a significant reduction in the number of squat repetitions performed. Torque at 0.52 rad from full extension (T30) was not significantly altered by carbohydrate restriction. Plasma lactate concentration postexercise was significantly lower after carbohydrate restriction. The fact that carbohydrate restriction reduces performance in isoinertial but not isokinetic strength exercise may be due to the different metabolic demands associated with the different exercise protocols used in the two modes of strength exercise.